TV Repair


Sci.Electronics FAQ: Repair: TV Repair
Notes on TV Repair and Diagnosis
INDEX
V2.20 (3/26/96)
Table of Contents
Chapter 1) About the Author & Copyright
Chapter 2) Introduction
2.1) Television at the crossroads
2.2) Television receiver fundamentals
2.3) TV repair
2.4) Repair or replace
Chapter 3) TV Receivers 101
3.1) Subsystems of a television set
3.2) For more information on TV technology
Chapter 4) CRT Basics
4.1) Color CRTs, Shadowmasks, Magnetic Fields, and Degauss
4.2) Why is the Shadowmask or Aperture Grill made of a magnetic material?
4.3) Tubes for all Nations
4.4) Degaussing (demagnetizing) a CRT
4.5) Why are indirectly heated cathodes used in CRT
4.6) Why do TVs overscan?
4.7) Scratches in CRT face
Chapter 5) TV Placement and Preventive Maintenance
5.1) General TV placement considerations
5.2) Preventive maintenance
Chapter 6) TV Troubleshooting
6.1) Safety
6.2) Safety Guidelines
6.3) Troubleshooting tips
6.4) Test equipment
6.5) Incredibly Handy widgets
6.6) Safe discharging of capacitors in TVs and video monitors
6.7) The series light bulb trick
6.8) Getting inside a TV
6.9) Dusting out the inside of a TV
Chapter 7) TV Adjustments
7.1) User picture adjustment
7.2) Focus adjustment
7.3) Adjustment of the internal SCREEN and color controls
7.4) Color Balance
7.5) Horizontal position, size, and linearity adjustment
7.6) Vertical position, size, and linearity adjustment
7.7) Pincushion adjustments
7.8) Geometry adjustment
7.9) Why is the convergence on my set bad near the edges
7.10) CRT purity and convergence problem
7.11) CRT purity adjustment
7.12) CRT convergence adjustment
7.13) Tilted picture
Chapter 8) Low Voltage Power Supply Problems
8.1) Low voltage power supply fundamentals
8.2) Power button on set is flakey
8.3) TV blows fuse
8.4) Internal fuse blew during lightening storm (or elephant hit power pole)
8.5) Fuse replaced but TV clicks with power-on but no other action
8.6) Power-on tick-tick-tick or click-click-click but no other action
8.7) No picture or raster and no sound
8.8) Reduced width picture and/or hum bars in picture and/or hum in sound
8.9) TV power cycling on and off
8.10) Dead TV with periodic tweet-tweet-tweet or flub-flub-flub
8.11) Shorted Components
8.12) Startup problems - nothing happens, click, or tick-tick-tick sound
8.13) TV turns off after warming up
8.14) TV doesn't power up immediately
8.15) Old TV requires warmup period
8.16) Relays in the Power Circuitry of TVs
8.17) Flameproof Resistors
Chapter 9) Deflection Problems
9.1) Deflection fundamentals
9.2) Why are nearly all horizontal drivers circuits transformer coupled?
9.3) Picture squeezed in then died
9.4) Horizontal deflection shutting down
9.5) Horizontal lock lost
9.6) Vertical squashed
9.7) Part of picture cut off
9.8) Single Vertical Line
9.9) Single Horizontal Line
9.10) Loss of Horizontal Sync (also applies to vertical) after Warmup
9.11) Intermittent jumping or jittering of picture or other random behavior
9.12) Horizontal output transistors keep blowing
9.13) Vertical foldover
9.14) Squashed picture on late model GE, RCA, or ProScan TV
9.15) Pincushioning Problems
9.16) Testing of flyback (LOPT) transformers
Chapter 10) High Voltage Power Supply Problems
10.1) HV power supply fundamentals
10.2) What is a tripler?
10.3) High voltage shutdown due to X-ray protection circuits
10.4) Low or no high voltage
10.5) Excessive high voltage
10.6) Arcing, sparking, or corona from CRT HV anode (red wire/suction cup)
10.7) Arcing at CRT sparkgaps
10.8) Arcing from flyback or vicinity
10.9) Ozone smell and/or smoke from TV
10.10) Should I be worried about X-ray exposure while servicing a TV or monitor?
10.11) Flyback shot by 4 year old
Chapter 11) Raster, Color, and Video Problems
11.1) No color - black and white picture
11.2) Psychodelic color
11.3) TV and Monitor Manufacturing Quality and Cold Solder Joints
11.4) Intermittent or Missing Colors
11.5) Red, green, or blue full on - fog over picture
11.6) Providing isolation for a CRT H-K short
11.7) Rescuing a shorted CRT
11.8) Brightening an old CRT
11.9) Bleeding highlights
11.10) Trailing lines on one or more colors
11.11) Picture fades in and out
11.12) Occasional brightness flashes
11.13) Excessive brightness and/or washed out picture
11.14) Bad focus (fuzzy picture)
11.15) Focus drift with warmup or age
11.16) Bad focus and adjustment changes brightness
11.17) Blank picture, good channel tuning and sound
11.18) Purple blob - or worse
11.19) Color TV only displays one color
11.20) Disappearing Red (or other color)
Chapter 12) Tuner and AGC Problems
12.1) No reception from antenna or cable
12.2) Picture is overloaded, washed out, or noisy
12.3) Interference when using VCR RF connection
12.4) Missing or noisy channel or block of channels
12.5) Loss of Channel after Warmup
12.6) Channel tuning drifts as set warms up
12.7) Noise in picture and sound due to bright scene
Chapter 13) Audio Problems
13.1) Picture fine, no audio
13.2) Weak or distorted audio
13.3) Buzzing TV
13.4) High pitched whine or squeal from TV with no other symptoms
Chapter 14) Miscellaneous Problems
14.1) General erratic behavior
14.2) Jittering or flickering due to problems with AC power
14.3) My TV has the shakes
14.4) TV was rained on
14.5) TV was dropped
14.6) Setup menus will not go away or hieroglyphics on screen
14.7) Setup Adjustments Lost
14.8) TV doesn't work after being in storage
14.9) Older TVs with multiple intermittent problems
14.10) TV has burning smell
14.11) Revival of dead or tired remote control units
14.12) Loudspeakers and TVs
14.13) Should I replace all the electrolytic capacitors if I find a bad one?
14.14) Phantom spot or blob on CRT after set is shut off
14.15) Disposing of dead TVs (CRTs and charged HV capacitors)
Chapter 15) Items of Interest
15.1) An informal history of X-ray protection
15.2) Memory chips in TVs
15.3) Tony's notes on setting convergence on delta gun CRTs
15.4) Saga and general setup for large CRT TVs
15.5) About Instant On TVs
15.6) Can I add an S-Video input to my TV or VCR?
15.7) How do I add A/V inputs to a TV which does not have them built in?
15.8) Turning a TV (or monitor) into an oscilloscope?
15.9) Displaying a video signal as a picture on an oscilloscope
15.10) Use of surge suppressors and line filters
15.11) GFCI tripping with monitor (or other high tech equipment)
15.12) Multisystem TVs
15.13) Could a TV be modified for 3D (stereo) display?
15.14) Displaying TV on a computer monitor
15.15) Displaying computer video on a TV
15.16) What is Kell factor with respect to interlaced displays?
15.17) Homemade V-chip (or at least viewing limiter
15.18) Interesting TV Switch Mode Power Supply
15.19) IR detector circuit
Chapter 16) International Color Television Standards
16.1) Some questions and answers about TV standards
16.2) Politically Correct TV Standards
16.3) Variations on a 'standard' - the PAL system
16.4) Color television standards worldwide
16.5) Cable channel allocation
16.6) Notes on cable and broadcast frequencies
16.7) Why is the NTSC color subcarrier such a weird frequency?
16.8) What is the maximal allowed deviation of the horizontal frequency?
16.9) Informal comparison of TV standards
Chapter 17) Repair Information and Parts Sources
17.1) Advanced TV troubleshooting
17.2) Service manuals for really old TVs
17.3) Parts information
17.4) Information sources on the Internet
17.5) Suggested references
17.6) Interchangeability of components
17.7) Repair parts sources:
Chapter 1) About the Author & Copyright
Author: Samuel M. Goldwasser
E-Mail: sam@stdavids.picker.com
Copyright (c) 1994, 1995, 1996
All Rights Reserved
Reproduction of this document in whole or in part is permitted if both
of the following conditions are satisfied:
This notice is included in its entirety at the beginning.
There is no charge except to cover the costs of copying.
Chapter 2) Introduction
2.1) Television at the crossroads
 
Television in substantially its present form has been with us for nearly
50 years. It is a tribute to the National Television Standards Committee
(NTSC) that the color television standards agreed upon in the early 1950s
have performed remarkably well making quite efficient use of valuable radio
spectrum space and the psychovisual characteristics of the human eye-brain
system. However, HDTV (High Definition TV) will supplant and ultimately
replace the current standards. We will all come to expect its superior
resolution, freedom from noise and ghosting, and CD sound. Yet, the
perceived quality of TV broadcasts and cable will never likely be the major
issue with most consumers. Content will continue to be the biggest problem.
 
It is likely that in roughly 15 years, HDTV - digitally processed and
transmitted as 1s and 0s - will completely replace the current system.
Acceptance in the marketplace is by no means assured but with the merging
of TV and computers - with the Internet as a driving force - it would seem
that the days of the stand-alone analog TV set are numbered.
 
2.2) Television receiver fundamentals
 
The basic color television receiver must perform the same functions today as
40 years ago. (Since B/W is a subset of the color standard, most references
in this document will be for color except as noted). A studio video monitor
includes all of the functions of a television receiver except the tuner
and IF (which rarely fail except for bad connections or perhaps lightening
strikes to the antenna or cable connection). Therefore most
of the repair information in this document is applicable to both TVs and
studio monitors. Modern computer monitors share many similarities with
TVs but the multisync and high scan rate deflection circuitry and more
sophisticated power supplies complicates their servicing.
 
As of this writing, all but the smallest TVs are based on the Cathode
Ray Tube (CRT) as the display device. Tiny pocket sets, camcorder
viewfinders, and the like have started using LCD (Liquid Crystal Display)
panels but these are still inferior to the CRT for real time video.
There has always been talk of 'the picture on the wall' display. While
we are closer than ever to this possibility, I believe that mass production
of an affordable wall mural TV screen is still decades away. The reason
is simple economics - it is really hard to beat the simplicity of the
shadowmask CRT. For example, a decent quality active matrix color LCD
panel may add $1000 to the cost of a notebook computer compared to $200
for a VGA monitor. More of these panels go in the dumpster than make it
to product do to manufacturing imperfections.
 
Projection - large screen - TVs may, on the other hand, be able to take
advantage of a novel development in integrated micromachining - the
Texas Instruments Inc. Digital Micromirror Device (DMD). This is basically
an integrated circuit with a tiltable micromirror for each pixel fabricated
on top of a static memory - RAM - cell. This technology would
permit nearly any size projection display to be produced and would
therefore be applicable to HDTV. Since it is a reflective device, the
light source can be as bright as needed. However, this is still not
a commercial product but stay tuned.
 
2.3) TV repair
 
Unlike VCRs or CD players where any disasters are likely to only affect
your pocketbook, TVs can be dangerous. Read, understand, and follow the
set of safety guidelines provided later in this section whenever working
on TVs, monitors, or other similar high voltage equipment.
 
If you do go inside, beware: line voltage (on large caps) and high voltage
(on CRT) for long after the plug is pulled. There is the added danger of
CRT implosion for carelessly dropped tools and often sharp sheetmetal
shields which can injure if you should have a reflex reaction upon touching
something you should not touch. In inside of a TV or monitor is no place
for the careless or naive.
 
Having said that, a basic knowledge of how a TV set works and what can
go wrong can be of great value even if you do not attempt the repair yourself.
It will enable you to intelligently deal with the service technician. You
will be more likely to be able to recognize if you are being taken for a ride
by a dishonest or just plain incompetent repair center. For example, a
faulty picture tube CANNOT be the cause of a color television only displaying
shows in black-and-white. The majority of consumers probably do not know even
this simple fact. Such a problem is usually due to a bad capacitor or other
10 cent part.
 
This document will provide you with the knowledge to deal with a large
percentage of the problems you are likely to encounter with your TVs.
It will enable you to diagnose problems and in many cases, correct them
as well. With minor exceptions, specific manufacturers and models
will not be covered as there are so many variations that such a treatment would
require a huge and very detailed text. Rather, the most common problems
will be addressed and enough basic principles of operation will be provided
to enable you to narrow the problem down and likely determine a course of
action for repair. In many cases, you will be able to do what is required
for a fraction of the cost that would be charged by a repair center.
 
Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair. It will also be easier to do
further research using a repair text such as the ones listed at the end of
this document. In any case, you will have the satisfaction of knowing you
did as much as you could before taking it in for professional repair.
With your new-found knowledge, you will have the upper hand and will not
easily be snowed by a dishonest or incompetent technician.
 
2.4) Repair or replace
 
If you need to send or take the TV to a service center, the repair
could easily exceed half the cost of a new TV. Service centers
may charge up to $50 or more for providing an initial estimate of repair
costs but this will usually be credited toward the total cost of the repair
(of course, they may just jack this up to compensate for their bench time).
 
TV prices have been dropping almost as fast as PC prices. Therefore, paying
such prices for repair just may not make sense. Except for picture tube
problems, most TV faults can be corrected without expensive parts, however.
Keeping a 5 year old TV alive may be well worthwhile as basic TV performance
and important features have not changed in a long time.
 
If you can do the repairs yourself, the equation changes dramatically as
your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free. The educational aspects may also be
appealing. You will learn a lot in the process. Thus, it may make sense
to repair that old clunker for your game room or beach house. (I would
suggest the kid's room but most TV watching just rots the brain anyhow so
a broken TV may be more worthwhile educationally than one that works.)
Chapter 3) TV Receivers 101
 
3.1) Subsystems of a television set
 
A TV set includes the following functional blocks:
 
Low voltage power supply (some may also be part of (2)). Most of the lower
    voltages used in the TV may be derived from the horizontal deflection
    circuits. Sometimes, there is a separate switching power supply but
    this would be the exception. Rectifier/filter capacitor/regulator from AC
    line provides the B+ to the switching power supply or horizontal
    deflection system. Degauss operates off of the line whenever power is
    turned on (after having been off for a few minutes) to demagnetize the CRT.
 
Horizontal deflection. These circuits provide the waveforms needed to
    sweep the electron beam in the CRT across and back some 15,734 times
    per second (for NTSC). The horizontal sync pulse from the sync separator
    locks the horizontal deflection to the video signal.
 
Vertical deflection. These circuits provide the waveforms needed to
    sweep the electron beam in the CRT from top to bottom and back 60 times
    per second (for NTSC). The vertical sync pulse from the sync separator
    locks the vertical deflection to the video signal.
 
CRT high voltage (also part of (2)). A modern color CRT requires
    up to 30 KV for a crisp bright picture. Rather than having a totally
    separate power supply, nearly every TV on the planet derives the HV
    (as well as many other voltages) from the horizontal deflection using
    a special transformer called a 'flyback' or 'Line OutPut Transformer (LOPT)
    for those of you on the other side of the lake.
 
Tuner, IF, AGC, video and audio demodulators. Input is the antenna or
    cable signal and output are baseband video and audio signals. There is
    usually someplace inside the TV where line level video and audio are
    present but it may not be accessible from the outside of the cabinet
    unless you paid for the more expensive model with the A/V option.
    Very often, the tuner is a shielded metal box positioned on the bottom
    right (as viewed from the front) separate from the main circuit board.
    Sometimes it is on the main circuit board. The IF section may be in
    either place.
 
    On older or cheap TVs with a knob tuner, this is usually mounted to the
    front panel by itself. There are usually separate boxes for the VHF and
    UHF tuners.
 
  Chroma demodulator. Input is the baseband video signal. Outputs are
    the individual signals for the red, green, and blue video to the CRT.
 
Video drivers (RGB). These are almost always located on a little
    circuit board plugged directly onto the neck of the CRT. They boost
    the output of the chroma demodulator to the hundred volts or so needed
    to drive the cathodes of the CRT.
 
Sync separator. Input is baseband video. Output is horizontal and
    vertical sync pulses to control the deflection circuits.
 
Audio amplifier/output. The line level audio is amplified to drive
    a set of speakers. If this is a stereo TV, then these circuits must
    also perform the stereo demultiplexing.
 
System control. Most modern TVs actually use a microcontroller - a fixed
    program microcomputer to perform all user interface and control functions
    from the front panel and remote control. These are becoming increasingly
    sophisticated. However, they do not fail often. Older TVs use a bunch
    of knobs and switches and these are prone to wear and dirt.
Most problems occur in the horizontal deflection and power supply sections.
These run at relatively high power levels and some components run hot.
The high voltage section is prone to breakdown and arcing as a result
of hairline cracks, humidity, dirt, etc.
 
The tuner components are usually quite reliable unless the antenna experiences
a lightening strike. However, it seems that even after 20+ years of
solid state TVs, manufacturers still cannot reliably solder the tuner
connectors and shields so that bad solder connections in these areas are
common even in new sets.
 
3.2) For more information on TV technology
 
The books listed in the section: Suggested references include additional
information on the theory and implementation of the technology of television
standards and TV receivers.
 
For an on line introduction to TV and monitor technology, point your
web browser to the Magnavox reference page at the following URL:
 
http://www.magnavox.com/electreference/electreference.html
 
There you will find links to a number of articles on the basic principles of
operation of CD players, laserdisc and optical drives, TVs, VCRs, camcorders,
loudspeakers, satellite receivers, and other consumer A/V equipment.
 
Chapter 4) CRT Basics
 
4.1) Color CRTs, Shadowmasks, Magnetic Fields, and Degauss
 
All color CRTs utilize a shadowmask or aperture grill a fraction of an inch
(1/2 typical) behind the phosphor screen to direct the electron beams
for the red, green, and blue video signals to the proper phosphor dots.
Since the electron beams for the R, G, and B phosphors originate from
slightly different positions (individual electron guns for each)
and thus arrive at slightly different angles, only the proper phosphors
are excited when the purity is properly adjusted and the necessary
magnetic field free region is maintained inside the CRT. Note that
purity determines that the correct video signal excites the
proper color while convergence determines the geometric
alignment of the 3 colors. Both are affected by magnetic fields.
Bad purity results in mottled or incorrect colors. Bad convergence
results in color fringing at edges of characters or graphics.
 
The shadowmask consists of a thin steel or InVar (a ferrous alloy)
with a fine array of holes - one for each trio of phosphor
dots - positioned about 1/2 inch behind the surface of the phosphor
screen. With most CRTs, the phosphors are arranged in triangular
formations called triads with each of the color dots at the apex
of the triangle. With many TVs and some monitors, they are
arranged as vertical slots with the phosphors for the 3 colors
next to one another.
 
An aperture grille, used exclusively in Sony Trinitrons (and now
their clones as well), replaces the shadowmask with an array of finely
tensioned vertical wires. Along with other characteristics of the
aperture grille approach, this permits a somewhat higher possible
brightness to be achieved and is more immune to other problems like
line induced moire and purity changes due to local heating causing
distortion of the shadowmask.
 
However, there are some disadvantages of the aperture grille design:
 
 weight - a heavy support structure must be provided for the tensioned
  wires (like a piano frame).
 
 price (proportional to weight).
 
 always a cylindrical screen (this may be considered an advantage
  depending on your preference.
 
 visible stabilizing wires which may be objectionable or unacceptable
  for certain applications.
 
Apparently, there is no known way around the need to keep the fine
wires from vibrating or changing position due to mechanical shock
in high resolution tubes and thus all Trinitron monitors require
1, 2, or 3 stabilizing wires (depending on tube size) across the
screen which can be see as very fine lines on bright images. Some
people find these wires to be objectionable and for some critical
applications, they may be unacceptable (e.g., medical diagnosis).
 
4.2) Why is the Shadowmask or Aperture Grill made of a magnetic material?
 
(From: Jeroen Stessen, (stessenj@am.umc.ce.philips.nl))
 
The question often arises: Well, if magnetization and the need for
degauss is a problem, why not make the shadowmask or aperture grille
from something that is non-magnetic?
 
The shadowmask MUST be made of magnetic material! This may seem
to be undesirable or counterintuitive but read on:
 
Together with the internal shielding hood it forms sort of a closed
space in which it is attempted to achieve a field-free space.
The purpose of degaussing is NOT to demagnetize the metal,
but to create a magnetization that compensates for the earth's
magnetic field. The SUM of the two fields must be near zero!
Degaussing coils create a strong alternating magnetic field
that gradually decays to zero. The effect is that the present
earth magnetic field is frozen into the magnetic shielding
and the field inside the shielding will be (almost) zero.
Non-zero field will cause colour purity errors.
 
Now you will understand why a CRT must be degaussed again
after it has been moved relative to the earth's magnetic field.
This will also explain why expensive computer monitors on a swivel
pedestal have a manual degaussing button, you must press it
every time after you have rotated the monitor.
 
The axial component of the magnetic field is harder to compensate
by means of degaussing. Better compensation may be achieved by
means of a rotation coil (around the neck or around the screen),
this requires an adjustment that depends on local magnetic field.
CRT's for moving vehicles (like military airplanes) may be
equipped with 6 coils to achieve zero magnetic field in all
directions. They use magnetic field sensors and active compensation,
thus they don't need any degaussing function. This is too
expensive for consumer equipment.
 
4.3) Tubes for all Nations
 
(From: Jeroen Stessen, (stessenj@am.umc.ce.philips.nl))
 
CRT Manufacturers actually make different versions of their tubes for
TV's for the northern and southern hemisphere, and sometimes a 3rd neutral
type. These are so-to-say precorrected for the uncompensated field. (Note
that the term 'tube' here includes much of the convergence hardware as
well - not just what is inside the glass.)
 
I remember when we exported projection televisions from Belgium to
Australia, a couple of years ago. They all had to be opened on arrival
to re-adjust the rotation settings on the convergence panel, due to
the different magnetic field in Australia. Projection TV's don't have
degaussing (there is nothing to degauss), and the customer can only
adjust red and blue shift, not rotation.
 
Our CRT application group has a magnetic cage. This is a wooden cube
(approx. 2 meter long sides) with copper coils around each of the 6
surfaces. With this they can simulate the earth magnetic field for
every place on earth (as indicated on a map on the wall).
 
4.4) Degaussing (demagnetizing) a CRT
 
Degaussing may be required if there are color purity problems with the
display. On rare occasions, there may be geometric distortion caused
by magnetic fields as well without color problems. The CRT can get
magnetized:
 
If the TV or monitor is moved or even just rotated.
 
If there has been a lightening strike nearby. A friend of mine
  had a lightening strike near his house which produced all of the
  effects of the EMP from a nuclear bomb.
 
If a permanent magnet was brought near the screen (e.g., kid's
  magnet or megawatt stereo speakers).
 
If some piece of electrical or electronic equipment with unshielded
  magnetic fields is in the vicinity of the TV or monitor.
 
Degaussing should be the first thing attempted whenever color
purity problems are detected. As noted below, first try the
internal degauss circuits of the TV or monitor by power cycling a few
times (on for a minute, off for 30 minutes, on for a minute, etc.)
If this does not help or does not completely cure the problem,
then you can try manually degaussing.
 
Commercial CRT Degaussers are available from parts distributors
like MCM Electronics and consist of a hundred or so turns of magnet wire
in a 6-12 inch coil. They include a line cord and momentary switch. You
flip on the switch, and bring the coil to within several inches of the
screen face. Then you slowly draw the center of the coil toward one edge
of the screen and trace the perimeter of the screen face. Then return to
the original position of the coil being flat against the center of the
screen. Next, slowly decrease the field to zero by backing straight up
across the room as you hold the coil. When you are farther than 5 feet
away you can release the line switch.
 
The key word here is SLOW. Go too fast and you will freeze the
instantaneous intensity of the 50/60 Hz AC magnetic field variation
into the ferrous components of the CRT and may make the problem worse.
It looks really cool to do this while the CRT is powered. The kids will
love the color effects.
Bulk tape erasers, tape head degaussers, open frame transformers, and the
ass-end of a weller soldering gun can be used as CRT demagnetizers but
it just takes a little longer. (Be careful not to scratch the screen
face with anything sharp.) It is imperative to have the CRT running when
using these whimpier approaches, so that you can see where there are
still impurities. Never release the power switch until you're 4 or 5
feet away from the screen or you'll have to start over.
I've never known of anything being damaged by excess manual degaussing
though I would recommend keeping really powerful bulk tape erasers turned
degaussers a couple of inches from the CRT.
If an AC degaussing coil or substitute is unavailable, I have even done
degaussed with a permanent magnet but this is not recommended since it is more
likely to make the problem worse than better. However, if the display
is unusable as is, then using a small magnet can do no harm. (Don't use
a 20 pound speaker or magnetron magnet as you may rip the shadowmask right
out of the CRT - well at least distort it beyond repair. What I have in
mind is something about as powerful as a refrigerator magnet.)
Keep degaussing fields away from magnetic media. It is a good idea to
avoid degaussing in a room with floppies or back-up tapes. When removing
media from a room remember to check desk drawers and manuals for stray
floppies, too.
It is unlikely that you could actually affect magnetic media but better
safe than sorry. Of the devices mentioned above, only a bulk eraser or
strong permanent magnet are likely to have any effect - and then only when
at extremely close range (direct contact with media container).
All color CRTs include a built-in degaussing coil wrapped around the
perimeter of the CRT face. These are activated each time the CRT is
powered up cold by a 3 terminal thermister device or other control
circuitry. This is why it is often suggested that color purity problems
may go away in a few days. It isn't a matter of time; it's the number
of cold power ups that causes it. It takes about 15 minutes of the power
being off for each cool down cycle. These built-in coils with thermal
control are never as effective as external coils.
4.5) Why are indirectly heated cathodes used in CRT
 
Here are three reasons:
The cathode can be made of and/or coated with a material optimal for
   emitting electrons without regard to its performance as a heater.
 
The separate cathode and filament can be electrically isolated so that
   the filament voltage and cathode drive signal, if any, do not interfere.
 
The cathode can have an optimal shape for the application. This would
   be particularly significant for CRTs. The spot on the screen is a
   reduced focused image of the effective shape of the emitting portion
   of the cathode.
4.6) Why do TVs overscan?
 
(The following includes material from:
  Jeroen Stessen (stessenj@am.nlvxe1.umc.ce.philips.nl))
 
Q: TVs are always set up to generate a picture which is 10-15 percent large
than the visible face of the CRT. Why?
 
In the early days of TV, this was probably done to make the design easier.
Component tolerances and power line voltage fluctuations would be masked even
if they caused changes in picture size.
 
There certainly is almost no reason today to have any more than a couple of
percent overscan. Most modern TVs have very well regulated power supplies
and component values do not really drift much.
 
Computer monitors, for example, are usually set up for no overscan at all
so that the entire image is visible.
 
We are constantly reminded of that, now that we are building TV's with
VGA inputs (PD5029C1 in the USA, US$ 2000). This mixed application has
overscan in TV mode and underscan in VGA mode. Geometry adjustment is
quite critical if you see border-on-border.
 
Unfortunately, TV's may be good but VCR's certainly are not. If you have
too little overscan and then put the VCR in any feature mode (like picture
search) then one (black) picture edge may become visible. Bad form.
Viewers do not like this.
 
While design considerations may have been the original reason for overscan,
now it has become accepted as a defacto standard, and broadcasters are
counting on the overscan being a certain percentage. One wonders whether
it will ever change or whether this really matters.
 
I suppose when we have true flat panel digitally addressed displays,
we might have 0% overscan.
 
At the Japan Electronics Show all the signs are pointed toward flat panel
displays so maybe I will not have to hold your breath for much longer.
 
Physically, as with an LCD display on a laptop computer, there will be
0% overscan (no need to build the extra pixels) but that doesn't mean
that all 480 lines will be visible.
 
4.7) Scratches in CRT face
 
Minor scratches can be removed with Jeweler's rouge or similar ultra fine
abrasive. Jeweler's Rouge is the same stuff that is used in the final
polishing of lenses and mirrors so it makes for a fine finish. However,
any kind of scratch deep enough to be felt will not yield to this approach.
 
WARNING: any kind of deep scratch on a CRT should be considered a serious
safety hazard. This may be even more of a concern for modern CRTs that
have 'integral implosion protection' - that steel band around the outside'.
Older CRTs used either (1) a separate safety shield - that laminated glass
plate in front of your grandmom's TV - or (2) a second contoured glass
panel bonded to the actual tube face. In both of these cases, the second
panel is strictly protective and serves no structural purpose. Therefore,
any damage to it does not compromise the tube in any way. In the case
of modern CRTs, the steel band in conjunction with the basic tube envelope
is used to maintain the integrity of the overall CRT. Any damage significantly
decreases the strength and increases the risk of CRT implosion.
 
BTW, scratches in the CRT have absolutely no effect on X-ray emission.
X-rays are blocked long before they come anywhere near the surface and
glass has very little effect on their direction. Any scratch deep enough
to have any detectable effect on X-ray emission (actually, it would need
to be an inch deep gouge) would have caused the tube to implode.
 
Chapter 5) TV Placement and Preventive Maintenance
5.1) General TV placement considerations
 
Proper care of a TV does not require much. Following the recommendations
below will assure long life and minimize repairs:
 
 Subdued lighting is preferred for best viewing conditions but I will not
  attempt to tell you how to arrange your room!
 
 Locate the TV away from extremes of hot and cold. Avoid damp or dusty
  locations if possible. (Right you say, keep dreaming!)
 
 Allow adequate ventilation - TVs use more power than any of your other
  A/V components. Heat buildup takes its toll on electronic components.
  Leave at least 3 inches on top and sides for air circulation if the
  entertainment center does not have a wide open back panel. Do not
  pile other components like VCRs on top of the TV if possible (see below).
 
 Do not put anything on top of the TV that might block the ventilation
  grill in the rear or top of the cover. This is the major avenue for
  the convection needed to cool internal components.
 
 If possible, locate the VCR away from the TV. Some VCRs are particularly
  sensitive to interference from the TV's circuitry and while this won't
  usually damage anything, it may make for less than optimal performance
  due to RF interference. The reverse is sometimes true as well.
 
 If possible, locate your computer monitor away from the TV. Interaction
  of the electromagnetic fields of the deflection systems may result in
  one or both displays jiggling, wiggling, or vibrating.
 
 Locate loudspeakers and other sources of magnetic fields at least a couple
  of feet from the TV. This will minimize the possibility of color purity
  or geometry problems.
 
 Make sure all input-output video and audio connections are tight and
  secure to minimize intermittent or noisy pictures and sound. Use proper
  high quality cable only long enough to make connections conveniently.
 
 Finally, store video cassettes well away from all electronic equipment
  including and especially loudspeakers. Heat and magnetic fields will
  rapidly turn your priceless video collection into so much trash. The
  operation of the TV depends on magnetic fields for beam deflection.
  Enough said.
 
5.2) Preventive maintenance
 
Preventive maintenance for a TV is pretty simple - just keep the case clean
and free of obstructions. Clean the screen with a soft cloth just dampened
with water and at most, mild detergent. DO NOT use anything so wet that
liquid may seep inside of the set around the edge of the picture tube - you
could end up with a very expensive repair bill when the liquid shorts out
the main circuit board lurking just below. If the set has a protective
flat glass faceplate, there is usually an easy way (on newer sets with this
type of protection) of removing it to get at the inner face of the CRT. Clean
both the CRT and the protective glass with a soft damp cloth and dry
thoroughly. If you have not cleaned the screen for quite a while, you will
be amazed at the amount of black grime that collects due to the static
buildup from the high voltage CRT supply.
 
In really dusty situations, periodically vacuuming inside the case and the use
of contact cleaner for the controls might be a good idea but realistically,
you will not do this so don't worry about it.
 
Chapter 6) TV Troubleshooting
 
6.1) Safety
 
TVs and computer or video monitors are among the more dangerous of consumer
electronics equipment when it comes to servicing. (Microwave ovens are
probably the most hazardous due to high voltage at high power.)
 
There are two areas which have particularly nasty electrical dangers:
the non-isolated line power supply and the CRT high voltage.
 
Major parts of nearly all modern TVs and many computer monitors are directly
connected to the AC line - there is no power transformer to provide the
essential barrier for safety and to minimize the risk of equipment damage.
In the majority of designs, the live parts of the TV or monitor are limited
to the AC input and line filter, degauss circuit, bridge rectifier and main
filter capacitor(s), low voltage (B+) regulator (if any), horizontal output
transistor and primary side of the flyback (LOPT) transformer, and parts
of the startup circuit and standby power supply. The flyback generates most
of the other voltages used in the unit and provides an isolation barrier so
that the signal circuits are not line connected and safer.
 
Since a bridge rectifier is generally used in the power supply, both
directions of the polarized plug result in dangerous conditions and an
isolation transformer really should be used - to protect you, your test
equipment, and the TV, from serious damage. Some TVs do not have any
isolation barrier whatsoever - the entire chassis is live. These are
particularly nasty.
 
The high voltage to the CRT, while 200 times greater than the line input,
is not nearly as dangerous for several reasons. First, it is present in a
very limited area of the TV or monitor - from the output of the flyback
to the CRT anode via the fat red wire and suction cup connector. If you
don't need to remove the mainboard or replace the flyback or CRT, then
leave it alone and it should not bite. Furthermore, while the shock from
the HV can be quite painful due to the capacitance of the CRT envelope, it
is not nearly as likely to be lethal since the current available from the
line connected power supply is much greater.
 
6.2) Safety Guidelines
 
These guidelines are to protect you from potentially deadly electrical shock
hazards as well as the equipment from accidental damage.
 
Note that the danger to you is not only in your body providing a conducting
path, particularly through your heart. Any involuntary muscle contractions
caused by a shock, while perhaps harmless in themselves, may cause collateral
damage - there are many sharp edges inside this type of equipment as well as
other electrically live parts you may contact accidentally.
 
The purpose of this set of guidelines is not to frighten you but rather to
make you aware of the appropriate precautions. Repair of TVs, monitors,
microwave ovens, and other consumer and industrial equipment can be both
rewarding and economical. Just be sure that it is also safe!
 
 Don't work alone - in the event of an emergency another person's presence
  may be essential.
 
 Always keep one hand in your pocket when anywhere around a powered
  line-connected or high voltage system.
 
 Wear rubber bottom shoes or sneakers.
 
 Don't wear any jewelry or other articles that could accidentally contact
  circuitry and conduct current, or get caught in moving parts.
 
 Set up your work area away from possible grounds that you may accidentally
  contact.
 
 Know your equipment: TVs and monitors may use parts of the metal chassis
  as ground return yet the chassis may be electrically live with respect to the
  earth ground of the AC line. Microwave ovens use the chassis as ground
  return for the high voltage. In addition, do not assume that the chassis
  is a suitable ground for your test equipment!
 
 If circuit boards need to be removed from their mountings, put insulating
  material between the boards and anything they may short to. Hold them in
  place with string or electrical tape. Prop them up with insulation sticks -
  plastic or wood.
 
 If you need to probe, solder, or otherwise touch circuits with power off,
  discharge (across) large power supply filter capacitors with a 2 W or greater
  resistor of 100-500 ohms/V approximate value (e.g., for a 200 V capacitor,
  use a 20K-100K ohm resistor). Monitor while discharging and/or verify that
  there is no residual charge with a suitable voltmeter. In a TV or monitor,
  if you are removing the high voltage connection to the CRT (to replace the
  flyback transformer for example) first discharge the CRT contact (under the
  insulating cup at the end of the fat red wire). Use a 1M-10M ohm 1W or
  greater wattage resistor on the end of an insulating stick or the probe
  of a high voltage meter. Discharge to the metal frame which is connected
  to the outside of the CRT.
 
 For TVs and monitors in particular, there is the additional danger of
  CRT implosion - take care not to bang the CRT envelope with your tools.
  An implosion will scatter shards of glass at high velocity in every
  direction. There are several tons of force attempting to crush the typical
  CRT. Always wear eye protection.
 
 Connect/disconnect any test leads with the equipment unpowered and
  unplugged. Use clip leads or solder temporary wires to reach cramped
  locations or difficult to access locations.
 
 If you must probe live, put electrical tape over all but the last 1/16
  of the test probes to avoid the possibility of an accidental short which
  could cause damage to various components. Clip the reference end of the
  meter or scope to the appropriate ground return so that you need to only
  probe with one hand.
 
 Perform as many tests as possible with power off and the equipment unplugged.
  For example, the semiconductors in the power supply section of a TV or
  monitor can be tested for short circuits with an ohmmeter.
 
 Use an isolation transformer if there is any chance of contacting line
  connected circuits. A Variac(tm) is not an isolation transformer!
  The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a
  good idea but will not protect you from shock from many points in a line
  connected TV or monitor, or the high voltage side of a microwave oven, for
  example. (Note however, that, a GFCI may nuisanse trip at power-on or at
  other random times due to leakage paths (like your scope probe ground) or
  the highly capacitive or inductive input characteristics of line powered
  equipment.) A fuse or circuit breaker is too slow and insensitive to provide
  any protection for you or in many cases, your equipment. However, these
  devices may save your scope probe ground wire should you accidentally connect
  it to a live chassis.
 
 Don't attempt repair work when you are tired. Not only will you be more
  careless, but your primary diagnostic tool - deductive reasoning - will
  not be operating at full capacity.
 
 Finally, never assume anything without checking it out for yourself!
  Don't take shortcuts!
 
6.3) Troubleshooting tips
 
Many problems have simple solutions. Don't immediately assume that
your problem is some combination of esoteric complex convoluted
failures. For a TV, it may just be a bad connection or blown fuse. Remember
that the problems with the most catastrophic impact on operation like a dead
TV usually have the simplest solutions. The kind of problems we would
like to avoid at all costs are the ones that are intermittent
or difficult to reproduce: the occasional interference or a TV that
refuses to play 'StarTrek Voyager'.
 
If you get stuck, sleep on it. Sometimes, just letting the problem
bounce around in your head will lead to a different more successful
approach or solution. Don't work when you are really tired - it is both
dangerous (especially with respect to TVs) and mostly non-productive
(or possibly destructive).
 
Whenever working on precision equipment, make copious notes and diagrams.
You will be eternally grateful when the time comes to reassemble the unit.
Most connectors are keyed against incorrect insertion or interchange
of cables, but not always. Apparently identical screws may be of differing
lengths or have slightly different thread types. Little parts may fit in
more than one place or orientation. Etc. Etc.
 
Pill bottles, film canisters, and plastic ice cube trays come in handy for
sorting and storing screws and other small parts after disassembly. This
is particularly true if you have repairs on multiple pieces of equipment
under way simultaneously.
 
Select a work area which is wide open, well lighted, and where dropped
parts can be located - not on a deep pile shag rug. The best location will
also be relatively dust free and allow you to suspend your troubleshooting
to eat or sleep or think without having to pile everything into a cardboard
box for storage.
 
Another consideration is ESD - Electro-Static Discharge. Some components
(like ICs) in a TV are vulnerable to ESD. There is no need to go overboard
but taking reasonable precautions such as getting into the habit of touching
the chassis first before any of the electronic components is a good practice.
 
A basic set of precision hand tools will be all you need to disassemble
a TV and perform most adjustments. These do not need to be really
expensive but poor quality tools are worse than useless and can cause
damage. Needed tools include a selection of Philips and straight blade
screwdrivers, socket drivers, needlenose pliers, wire cutters, tweezers,
and dental picks. For adjustments, a miniature (1/16 blade) screwdriver
with a non-metallic tip is desirable both to prevent the presence of
metal from altering the electrical properties of the circuit and to
minimize the possibility of shorting something from accidental contact
with the circuitry. A set of plastic alignment tools will be useful for
making adjustments to coils and RF transformers.
 
A low power (e.g., 25 W) fine tip soldering iron and fine rosin core solder
will be needed if you should need to disconnect any soldered wires (on purpose
or by accident) or replace soldered components. A higher power iron or small
soldering gun will be needed for dealing with larger components.
 
For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller'
(they are the same) and a heat gun or blow dryer come in handy to identify
components whose characteristics may be drifting with temperature. Using the
extension tube of the spray can or making a cardboard nozzle for the heat
gun can provide very precise control of which components you are affecting.
 
For info on useful chemicals, adhesives, and lubricants, see
Repair Briefs, an Introduction
as well as other documents available at this site.
6.4) Test equipment
Don't start with the electronic test equipment, start with some analytical
thinking. Your powers of observation (and a little experience) will make
a good start. Your built in senses and that stuff between
your ears represents the most important test equipment you have.
 
However, some test equipment will be needed:
 Multitester (DMM or VOM) - This is essential for checking of power supply
  voltages and voltages on the pins of ICs or other components - service
  literature like the SAMs Photofacts described elsewhere in this document
  include voltage measurements at nearly every circuit tie point for properly
  functioning equipment. The multitester will also be used to check
  components like transistors, resistors, and capacitors for correct value
  and for shorts or opens. You do not need a fancy instrument. A basic
  DMM - as long as it is reliable - will suffice for most troubleshooting.
  If you want one that will last for many years, go with a Fluke. However,
  even the mid range DMMs from Radio Shack have proven to be reliable and
  of acceptable accuracy. For some kinds of measurements - to deduce         trends
  for example - an analog VOM is preferred (though some DMMs have a bar graph
  scale which almost as good).
 
 Oscilloscope - While many problems can be dealt with using just a multimeter,
  a 'scope will be essential as you get more into advanced troubleshooting.
  Basic requirements are: dual trace, 10-20 MHz minimum vertical bandwidth,
  delayed sweep desirable but not essential. A good set of proper 10x/1x
  probes. Higher vertical bandwidth is desirable but most consumer electronics
  work can be done with a 10 MHz scope. A storage scope or digital scope
  might be desirable for certain tasks but is by no means essential for basic
  troubleshooting.
 
  I would recommend a good used Tektronix or HP scope over a new
  scope of almost any other brand. You will usually get more scope
  for your money and these things last almost forever. My 'good' scope
  is the militarized version (AN/USM-281A) of the HP180 lab scope. This
  has a dual channel 50 MHz vertical plugin and a delayed sweep horizontal
  plugin. I have seen these going for under $300 from surplus outfits.
  For a little more money, you can get a Tek 465 100 Mhz scope ($400-700)
  which will suffice for all but the most demanding (read: RF or high
  speed digital) repairs.
 
 A video signal source - both RF and baseband (RCA jacks). Unless you
  are troubleshooting tuner or video/audio input problems, either one
  will suffice. RF sources include a pair of rabbit ears or an outdoor
  antenna, a cable connection, or a VCR with a working RF modulator.
  This will be more convenient than an antenna connection and will permit
  you to control the program material. In fact, making some test tapes
  using a camcorder or video camera to record static test patterns will
  allow you full control of what is being displayed and for how long.
 
 Color bar/dot/crosshatch signal generator. This is a useful piece
  of equipment if you are doing a lot of TV or monitor repair and need
  to perform CRT convergence and chroma adjustments. However, there
  are alternatives that are almost as good: a VHS recording of these
  test patterns will work for TVs. A PC programmed to output a suitable
  set of test patterns will be fine for monitors (and TVs if you can set
  up the video card to produce an NTSC/PAL signal. This can be put
  through a VCR to generate the RF (Channel 3/4) input to your TV if
  it does not have direct video inputs (RCA jacks).
 
6.5) Incredibly Handy widgets
 
These are the little gadgets and homemade testers that are useful for many
repair situations. Here are just a few of the most basic:
 
 Series light bulb for current limiting during the testing of TVs,
  monitors, switching power supplies, audio power amplifiers, etc. I built
  a dual outlet box with the outlets wired in series so that a lamp
  can be plugged into one outlet and the device under test into the other.
  For added versatility, add a regular outlet and 'kill' switch using a
  quad box instead. The use of a series load will prevent your expensive
  replacement part like a horizontal output transistor from blowing if
  there is still some fault in the circuit you have failed to locate.
 
 A Variac. It doesn't need to be large - a 2 A Variac mounted with
  a switch, outlet and fuse will suffice for most tasks. However,
  a 5 amp or larger Variac is desirable. If you will be troubleshooting
  220 VAC equipment in the US, there are Variacs that will output 0-240 VAC
  from a 115 VAC line (just make sure you don't forget that this can easily
  fry your 115 VAC equipment.) By varying the line voltage, not only can
  you bring up a newly repaired TV gradually to make sure there are no
  problems but you can also evaluate behavior at low and high line voltage.
  This can greatly aid in troubleshooting power supply problems. WARNING: a
  Variac is not an isolation transformer and does not help with respect
  to safety. You need an isolation transformer as well.
 
 Isolation transformer. This is very important for safely working on
  live chassis equipment. Since all modern TVs use a line connected power
  supply, it is essential. You can build one from a pair of similar
  power transformers back-to-back (with their highest rated secondaries
  connected together. I built mine from a couple of similar old
  tube type TV power transformers mounted on a board with an outlet box
  including a fuse. Their high voltage windings were connected together.
  The unused low voltage windings can be put in series with the primary
  or output windings to adjust voltage. Alternatively, commercial line
  isolation transformers suitable for TV troubleshooting are available
  for less than $100 - well worth every penny.
 
 Variable isolation transformer. You don't need to buy a fancy combination
  unit. A Variac can be followed by a normal isolation transformer. (The
  opposite order also works. There may be some subtle differences in
  load capacity.).
 
 Degaussing coil. Make or buy. The internal degaussing coil salvaged
  from a defunct TV doubled over to half it original diameter to increase
  its strength in series with a 200 W light bulb for current limiting will
  work just fine. Or, buy one from a place like MCM Electronics - about
  $15 for one suitable for all but the largest TVs. Also, see the section:
  Degaussing (demagnetizing) CRTs.
 
6.6) Safe discharging of capacitors in TVs and video monitors
 
It is essential - for your safety and to prevent damage to the device under
test as well as your test equipment - that large or high voltage capacitors
be fully discharged before measurements are made, soldering is attempted,
or the circuitry is touched in any way. Some of the large filter capacitors
commonly found in line operated equipment store a potentially lethal charge.
 
This doesn't mean that every one of the 250 capacitors in your TV need to be
discharged every time you power off and want to make a measurement. However,
the large main filter capacitors and other capacitors in the power supplies
should be checked and discharged if any significant voltage is found after
powering off (or before any testing - some capacitors (like the high voltage
of the CRT in a TV or video monitor) will retain a dangerous or at least
painful charge for days or longer!)
 
The technique I recommend is to use a high wattage resistor of about
100 ohms/V of the working voltage of the capacitor. This will
prevent the arc-welding associated with screwdriver discharge but will
have a short enough time constant so that the capacitor will drop to
a low voltage in at most a few seconds (dependent of course on the
RC time constant and its original voltage).
 
Then check with a voltmeter to be double sure. Better yet, monitor
while discharging (not needed for the CRT - discharge is nearly
instantaneous even with multi-M ohm resistor).
 
Obviously, make sure that you are well insulated!
 
 For the main capacitors in a switching power supply which might be
  100 uF at 350 V this would mean a 5K 10W resistor. RC=.5 second.
  5RC=2.5 seconds. A lower wattage resistor can be used since the total
  energy in not that great. The circuit described below can used to provide
  a visual indication of polarity and charge.
 
 For the CRT, use a high wattage (not for power but to hold off the high
  voltage which could jump across a tiny 1/4 watt job) resistor of a few
  M ohms discharged to the chassis ground connected to the outside of the
  CRT - NOT SIGNAL GROUND ON THE MAIN BOARD as you may damage sensitive
  circuitry. The time constant is very short - a ms or so. However, repeat
  a few times to be sure. (Using a shorting clip lead may not be a bad idea
  as well while working on the equipment - there have been too many stories
  of painful experiences from charge developing for whatever reasons ready
  to bite when the HV lead is reconnected.) Note that if you are touching the
  little board on the neck of the CRT, you may want to discharge the HV
  even if you are not disconnecting the fat red wire - the focus and screen
  (G2) voltages on that board are derived from the CRT HV.
 
  If you are not going to be removing the CRT anode connection, replacing
  the flyback, or going near the components on the little board on the neck
  of the CRT, I would just stay away from the fat red wire and what it is
  connected to including the focus and screen wires. Repeatedly shoving
  a screwdriver under the anode cap risks scratching the CRT envelope which
  is something you really do not want to do.
Again, always double check with a reliable voltmeter!
 
Reasons to use a resistor and not a screwdriver to discharge capacitors:
 
It will not destroy screwdrivers and capacitor terminals.
It will not damage the capacitor (due to the current pulse).
It will reduce your spouse's stress level in not having to hear those
scary snaps and crackles.
6.7) The series light bulb trick
 
When powering up a TV (or any other modern electronic devices with expensive
power semiconductors) that has had work done on any power circuits, it
is desirable to minimize the chance of blowing your newly installed parts
should there still be a fault. There are two ways of doing this: use of a
Variac to bring up the AC line voltage gradually and the use of a series load
to limit current to power semiconductors.
 
Actually using a series load - a light bulb is just a readily available
cheap load - is better than a Variac (well both might be better still) since
it will limit current to (hopefully) non-destructive levels.
 
What you want to do is limit current to the critical parts - usually the
horizontal output transistor (HOT). Most of the time you will get away with
putting it in series with the AC line. However, sometimes, putting a light
bulb directly in the B+ circuit will provide better protection as it will
limit the current out of the main filter capacitors to the HOT. Actually,
an actual power resistor is probably better as its resistance is constant
as opposed to a light bulb which will vary by 1:10 from cold to hot. The
light bulb, however, provides a nice visual indication of the current drawn
by the circuit under test. For example:
 
Full brightness: short circuit or extremely heavy load - a fault probably
  is still present.
 
Initially bright but then settles at reduced brightness: filter capacitors
  charge, then lower current to rest of circuit. This is what is expected
  when the equipment is operating normally. There could still be a problem
  with the power circuits but it will probably not result in an immediate
  catastrophic failure.
 
Pulsating: power supply is trying to come up but shutting down due to
  overcurrent or overvoltage condition. This could be due to a continuing
  fault or the light bulb may be too small for the equipment.
The following are suggested starting wattages:
 
 40 W bulb for VCR or laptop computer switching power supplies.
 100 W bulb for small (i.e., B/W or 13 inch color) TVs.
 150-200 W bulb for large color or projection TVs.
Depending on the power rating of the equipment, these wattages may need to be
increased. However, start low. If the bulb lights at full brightness,
you know there is still a major fault. If it flickers or the TV (or other
device) does not quite come fully up, then it should be safe to go to a
larger bulb.
 
6.8) Getting inside a TV
 
You will void the warranty - at least in principle. There are usually no
warranty seals on a TV so unless you cause visible damage or mangle the
screws, it is unlikely that this would be detected. You need to decide.
A TV still under warranty should probably be returned for warranty
service for any covered problems except those with the most obvious
and easy solutions. Another advantage of using warranty service is that
should your problem actually be covered by a design change, this will be
performed free of charge. And,
you cannot generally fix a problem which is due to poor design!
 
Getting into a TV is usually quite simple requiring the removal of anywhere
from 4 to 16 Philips or 1/4 hex head screws - most around the rear edge of the
cabinet or underneath, a couple perhaps in the middle. Disconnect the antenna
and/or antenna or cable wiring first as it may stay with catch on the rear
cover you are detaching. Reconnect whatever is needed for testing after the
cover is removed.
 
As you pull the cover straight back (usually) and off, make sure that no
other wires are still attached. Often, the main circuit board rests on
the bottom of the cover in some slots. Go slow as this circuit board may
try to come along with the back. Once the back is off, you may need to prop
the circuit board up with a block of wood to prevent stress damage and contact
with the work surface.
 
Most TVs can still be positioned stably on any of three sides (left, right,
bottom) even without the rear cover. However, some require the cover for
mechanical strength or to not easily fall over. Be careful- larger TVs,
in particular, are quite heavy and bulky. Get someone to help and take
precautions if yours is one of the unstable variety. If need be, the set
can usually safely be positioned on the CRT face if it is supported by
foam or a folded blanket.
 
Reassemble in reverse order. Getting the circuit board to slide smoothly
into its slots may take a couple of attempts but otherwise there should
be no surprises.
 
6.9) Dusting out the inside of a TV
 
The first thing you will notice when you remove the cover is how super
dusty everything is. Complements to the maid. You never dreamed there
was that much dust, dirt, and grime, in the entire house!
 
Use a soft brush (like a new paintbrush) and a vacuum cleaner to carefully
remove the built up dust. Blowing off the dust will likely not hurt the TV
unless it gets redeposited inside various controls or switches but will
be bad for your lungs - and will spread it all over the room. Don't turn
anything - many critical adjustments masquerade as screws that just beg to
be tightened. Resist the impulse for being neat and tidy until you know
exactly what you are doing. Be especially careful around the components on
the neck of the CRT - picture tube - as some of these are easily shifted
in position and control the most dreaded of adjustments - for color purity
and convergence. In particular, there will be a series of adjustable ring
magnets. It is a good idea to mark their position in any case with
some white paint, 'white out', or a Magic Marker so that if they do get
moved - or you move them deliberately, you will know where you started.
 
Chapter 7) TV Adjustments
 
7.1) User picture adjustment
 
For general viewing, subdued lighting but not total darkness is probably
best. However, for most dramatic impact, a darkened environment may be
preferred. Make the following adjustments under the expected viewing
conditions.
 
Tune to a strong channel or play a good quality tape.
 
Turn the brightness, contrast, and color controls all the way down. Center
the tint control (NTSC).
 
Increase the brightness until a raster is just visible in the darkest
(shadow) areas of the picture.
 
Increase the contrast until the desired intensity of highlights is obtained.
 
Since brightness and contrast are not always independent, go back and forth
until you get the best picture.
 
Initially adjust the color control for pastel shades rather than highly
saturated color. Set the tint control for best flesh tones. Then,
increase the color control to obtain the desired degree of color saturation.
 
7.2) Focus adjustment
 
On a decent TV, you should be able to make out the individual scanning
lines. If they are fuzzy, especially in bright areas, then focus may need
to be adjusted.
 
The focus pot is usually located on the flyback transformer or on an
auxiliary panel nearby. The focus wire usually comes from the flyback or
the general area or from a terminal on a voltage the multiplier module
(if used). It is usually a wire by itself going to the little board
on the neck of the CRT.
 
Let the set warm up for at least half an hour. Display a good quality
signal. Turn the user color control all the way down and the brightness
and contrast controls all the way up. This will be the worst case. Adjust
the focus control for best overall sharpness - you may not be able to get it
perfect everywhere - center as well as corners. If best focus is at one
end of the focus pot's range and still not good enough, there may be a
problem in the focus divider, focus pot, or some related component.
 
7.3) Adjustment of the internal SCREEN and color controls
 
The screen should be adjusted with a white pattern (snow from the tuner
should do or turn the user COLOR control all the way down to get a
black and white picture). Put the set in Service mode (horizontal line)
if it has such a switch in the back or inside. If not, just use
the raster in a darkened room. Adjust screen for a dim white
line (raster). If the line is not white at its dimmest point, you will
need to adjust the drive and cutoff controls for R, G, & B.
 
Alternatively, you can use the following procedure:
 
(From LEE)
Turn R, G, and B screen (or background) controls down. Now turn color
control fully counterclockwise -- off. Now turn up red screen until the
screen just shows a red hue. Now turn red gun down until red tint just goes
away. Now do the same with the green and blue screen controls. Now adjust the
two DRIVE controls for the best black and white picture. That's all there is
to it. I don't like to work with just a thin SETUP line. Cartoons seem to
be the best thing to have on while doing the above procedure. You can
also use just plain snow (no program) if you prefer. If you can obtain a
good B&W pic. when you're done, the tube is good and the set if most
likely functioning properly. Be patient and go slow while watching the
large mirror that you are using during this procedure.
 
7.4) Color Balance
 
Color balance needs adjustment if the highlights and/or shadows of a black
and white picture (turn the color control all the way down) are not a
perfectly neutral gray.
 
To adjust the color balance: Turn the color control all the way down so that
you get what should be a B/W picture. Set the user brightness and contrast
controls about mid-range. The tint control should not matter (if it does
at this point, you have other chroma problems or an 'autocolor' switch
is on limiting the range of some controls).
 
Adjust the sub-brightness controls (may be called color screen, background,
or the like) so that the dark areas of the picture are just visible and
neutral gray. Then, adjust the color gain controls until the brightest areas
are neutral white but not so bright that there is 'color bleeding' in
the highlights.
 
This should get you close. If something is still shifting after warmup and
get some cold-spray or even a little blower and try to locate the component
that is drifting. Most likely a transistor or capacitor.
 
7.5) Horizontal position, size, and linearity adjustment
Horizontal position may be set via a switch or jumper, a pot, or (mostly
in B/W TVs) a set of rings on the CRT neck.
Horizontal size should be set so that there is about 10-15 percent
overscan left and right. This will allow ample margin for power line
voltage fluctuations, component aging, and the reduction in raster size
that may occur with some VCR special effects (fast play) modes.
Many sets no longer have any horizontal size adjustments and depend on
accurate regulation of the voltage to the horizontal output stage
to control horizontal size. There may be a B+ adjustment to perform
first.
On those that do, the adjustment may either be done by setting the B+
voltage, by a pot, or a width coil in series with the horizontal
deflection coils.
 
Modern sets do not generally have any linearity control but you may find
this on older models. You will need to go back and forth between size
and linearity as these adjustments are usually not independent.
 
Some of the newest sets control all these parameters via settings in
non-volatile memory and use service menus accessed via the remote control
for nearly all setup adjustments.
 
7.6) Vertical position, size, and linearity adjustment
 
Vertical position may be set via a switch or jumper, a pot, or (mostly
in B/W TVs) a set of rings on the CRT neck.
 
Vertical size should be set so that there is about 10-15 percent
overscan top and bottom. This will allow ample margin for power line
voltage fluctuations, component aging, and the reduction in raster size
that may occur with some VCR special effects (fast play) modes.
 
Some sets no longer have any vertical size adjustments and depend on
the accurate regulation of the voltage to the vertical output stage
to control vertical size.
 
On those that do, the adjustment is usually a pot in the vertical output
circuitry. If your set has a linearity control, you will need to adjust
this in conjunction with the size control as these are usually not independent.
 
Some of the newest sets control all these parameters via settings in
non-volatile memory and use service menus accessed via the remote control
for nearly all setup.
 
7.7) Pincushion adjustments
 
There may be two controls - amplitude and phase. Pincushion amplitude
as its name implies, controls the size of the correction. Pincushion
phase affects where on the sides it is applied. Don't expect perfection.
 
If the controls have no effect, there is probably a fault in the pincushion
correction circuitry.
 
It is best to make these adjustments with a crosshatch or dot test pattern
 
7.8) Geometry adjustment
 
This refers to imperfections in the shape of the picture not handled
by the pincushion and size adjustments. These types of defects include
trapezoidal or keystone shaped raster and jogs or wiggles around the periphery
of the raster. Unfortunately, one way these are handled at the factory is to
glue little magnets to strategic locations on the CRT and/or rotate little
magnets mounted on the yoke frame. Unless you really cannot live with the
way it is (assuming there isn't something actually broken), leave these
alone! You can end up with worse problems. In any case, carefully mark the
position AND orientation of every magnet so that if this happens, you can
get back to where you started. If the magnets are on little swivels, some
experimenting with them one at a time may result in some improvement. Of
course, it is best to obtain a service manual and follow its instructions.
 
7.9) Why is the convergence on my set bad near the edges
 
Very simple - nothing is quite perfect. Perfect convergence is not
even necessarily possible in theory with the set of adjustments available
on a typical TV. It is all a matter of compromises. Consider what
you are trying to do: get three electron beams which originate from
different electron guns to meet at a single point within a fraction
of a mm everywhere on the screen. This while the beams are scanning
at an effective writing rate of 20,000 mph across the face of
a 27 CRT in a variable magnetic environment manufactured at a
price you can afford without a second mortgage!
 
7.10) CRT purity and convergence problem
 
Purity assures that each of the beams for the 3 primary colors -
red, green, and blue - strikes only the proper phosphor dots for that color.
A totally red scene will appear pure red and so forth. Symptoms of poor
purity are blotches of discoloration on the screen. Objects will change
shades of color when the move from one part of the screen to another.
 
Convergence refers to the control of the instantaneous positions of
the red, green, and blue spots as they scan across the face of the
CRT so that they are as nearly coincident as possible. Symptoms of
poor convergence are colored borders on solid objects or visible
separate R, G, and B images of fine lines or images,
 
NOTE: It is best to face the set North-South (front-to-back) when doing any
purity and convergence adjustments. Since you have no way of knowing
what orientation will eventually be used, this is the best compromise
as the earth's magnetic field will be aligned front-back. Of course, if
you know the final orientation of the TV in your entertainment center - and
you don't expect to be redecorating, use that instead.
 
First, make sure no sources of strong magnetic fields are in the vicinity of
the TV - loudspeakers, refrigerator magnets, MRI scanners, etc. A nearby
lightening strike or EMP from a nuclear explosion can also affect purity.
 
Cycle power a couple of times to degauss the CRT (1 minute on, 20 minutes
off) - see the section: Degaussing (demagnetizing) the CRT. If the built
in degaussing circuits have no effect, use an external manual degaussing coil.
 
Assuming this doesn't help, you will need to set the internal purity
and/or convergence adjustments on the CRT.
 
First, mark the positions of all adjustments - use white paint, 'White out',
or a Magic Marker on the ring magnets on the neck of the CRT, the position
and tilt of the deflection yoke, and any other controls that you may touch
deliberately or by accident.
 
NOTE: if your set is still of the type with a drawer or panel of knobs
for these adjustments, don't even think about doing anything without
a service manual and follow it to the letter unless the functions of all
the knobs is clearly marked (some manufacturers actually do a pretty good
job of this).
 
7.11) CRT purity adjustment
 
Purity on modern CRTs is usually set by a combination of a set of ring
magnets just behind the deflection yoke on the neck of the CRT and the
position of the yoke fore-aft. As always, mark the starting position of
all the rings and make sure you are adjusting the correct set if rings!
 
Use the following purity adjustment procedure as a general guide only.
Depending on the particular model TV, the following purity adjustment
procedure may substitute green for red. This depends on the gun placement
in the CRT. This description is based on the SAMs Photofact for the RCA
CTC111C chassis which uses a slot-mask CRT. The procedures for dot-mask
and Trinitron (aperture grille) CRTs will vary slightly.
See you service manual!
 
Obtain a white raster (sometimes there is a test point that can be grounded
to force this). Then, turn down the bias controls for blue and green so
that you have a pure red raster. Let the set warm up for a minimum of
15 minutes.
 
Loosen the deflection yoke clamp and move the yoke as far back as it will go,
 
Adjust the purity magnets to center the red vertical raster on the screen.
 
Move the yoke forward until you have the best overall red purity.
 
Now, move the yoke forward until you have the best overall red purity.
Tighten the clamp securely and reinstall the rubber wedges (if you set
has these) to stabilize the yoke position. Reset the video adjustments
you touched to get a red raster.
 
7.12) CRT convergence adjustment
 
In the good old days when TVs were TVs (and not just a picture tube with
a little circuit board attached) there were literally drawers full of
knobs for setting convergence. One could spend hours and still end up
with a less than satisfactory picture. As the technology progressed,
the number of electronic adjustments went down drastically so that today
there are very few if any.
 
Unless you want a lot of frustration, I would recommend not messing with
convergence. You could end up a lot worse. I have no idea what is used
for convergence on your set but convergence adjustments are never
quite independent of one another. You could find an adjustment that
fixes the problem you think you have only to discover some other area
of the screen is totally screwed. In addition, there are adjustments
for geometry and purity and maybe others that you may accidentally move
without even knowing it until you have buttoned up the set.
 
WARNING: Accurately mark the original positions - sometimes you will change
something that will not have an obvious effect but will be noticeable
later on. So it is extremely important to be able to get back to where
you started. If only red/green vertical lines are offset, then it is
likely that only a single ring needs to be moved - and by just a hair.
But, you may accidentally move something else!
 
If you really cannot live with it, make sure you mark everything very
carefully so you can get back to your current state.
A service manual is essential!
 
Convergence is set using a white crosshatch or dot test pattern. If you
do not have a test pattern generator, any static scene (from a camcorder
or previously recorded tape, for example) with a lot of fine detail will
suffice. Turn the color control all the way down so you have a B/W
picture.
 
Static convergence sets the beams to be coincident in the exact center of
the screen. This is done using a set of ring magnets behind the purity
magnets on the CRT neck.
 
From the SAMs for the RCA CTC111C: adjust the center set of magnets to
converge blue to green at the center of the screen. Adjust the rear set
of magnets to converge red to green at the center of the screen. Your
set may have a slightly different procedure.
 
Dynamic convergence adjusts for coincidence at the edges and corners.
 
On old tube, hybrid, and early solid state TVs, dynamic convergence was
accomplished with electronic adjustments of which there may have been
a dozen or more that were not independent. With modern sets, all convergence
is done with magnet rings on the neck of the CRT, magnets glued to the CRT,
and by tilting the deflection yoke. The clamp in conjunction with rubber
wedges or set screws assures that the yoke remains in position.
 
From the SAMs for the RCA CTC111C: Loosen the screws at the 6 o'clock and
10 o'clock positions to permit the yoke to be tilted vertically. Rock yoke
up and down to converge the right and left sides of the screen. Tighten screw
at 6 o'clock and loosen screw at 3 o'clock to permit the yoke to be tilted
horizontally. Rock yoke from side to side to converge the top and bottom
of the screen. Tighten screws at 3 o'clock and 10 o'clock.
 
Many sets simply use the main clamp which locks the yoke to the neck of the
CRT in conjunction with rubber wedges between the yoke and the funnel of
the CRT to stabilize the yoke position position.
 
Refer to your service manual. (Is this beginning to sound repetitious?
 
For additional comments on convergence adjustments, see the sections: Tony's
notes on setting convergence on delta gun CRTs and Saga and General setup
for large CRT TVs.
 
7.13) Tilted picture
 
You have just noticed that the picture on your fancy (or cheap) TV
is not quite horizontal - not aligned with the front bezel. Note that
often there is some keystoning as well where the top and bottom or left and
right edges of the picture are not quite parallel - which you may never
have noticed until now. Since this may not be correctable, adjusting
tilt may represent a compromise at best between top/bottom or left/right
alignment of the picture edges. You may never sleep again knowing that
your TV picture is not perfect! BTW, I can sympathize with your unhappiness.
Nothing is more annoying than a just noticeable imperfection such as this.
 
There are several possible causes for a tilted picture:
 
 You just became aware of it but nothing has changed. Don't dismiss this
   offhand. It is amazing how much we ignore unless it is brought to our
   attention. Are you a perfectionist?
 
 There is an external tilt control which may be misadjusted. Newer Sony
   monitors have this (don't know about TVs) - a most wonderful addition.
   Too bad about the stabilizing wires on Trinitron CRTs. A digital control
   may have lost its memory accidentally. The circuitry could have a problem.
 
 There is an internal tilt control that is misadjusted. Not common.
 
 The deflection yoke on the CRT has gotten rotated or was not oriented correctly at the time of the set's manufacture.
   Sometimes, the entire yoke is glued in place in addition to being clamped adding
   another complication. On some monitors, you can rotate the CRT slightly instead
   but probably not on your TV.
 
   If the TV was recently bumped or handled roughly, the yoke may have been
   knocked out of position. But in most cases, the amount of abuse required
   to do this with the yoke firmly clamped and/or glued would have totally
   destroyed the set in the process.
 
   There is a risk (in addition to the risk of frying yourself on the various
   voltages present inside as operating TV) of messing up the convergence
   or purity when fiddling with the yoke or anything around it since the yoke
   position on the neck of the tube and its tilt may affect purity and
   convergence. Tape any rubber wedges under the yoke securely in place
   as these will maintain the proper position and tilt of the yoke while you
   are messing with it. (Don't assume the existing tape will hold - the
   adhesive is probably dry and brittle).
 
External magnetic fields can sometimes cause a rotation without any other obvious effects
   - have you changed the TV's location?
Chapter 8) Low Voltage Power Supply Problems
8.1) Low voltage power supply fundamentals
 
TVs require a variety of voltages (at various power levels) to function.
The function of the low voltage power supply is to take the AC line input
of either 115 VAC 60 Hz (220 VAC 50 Hz or other AC power in Europe and
elsewhere) and produce some of these DC voltages. In all cases, the power
to the horizontal output transistor of the horizontal deflection system
is obtained directly from the low voltage power supply. In some cases,
a variety of other DC voltages are derived directly from the AC line by
rectification, filtering, and regulation. In other designs, however, most
of the low voltages are derived from secondary windings on the flyback
(LOPT) transformer of the horizontal deflection system. In still other
designs, there is a separate switchmode power supply that provides some or
all of these voltages. There are also various (and sometimes convoluted)
combinations of any or all of the above.
 
There will always be:
 
 A power switch, relay, or triac to enable main power.
 
 A set of rectifiers - usually in a bridge configuration - to turn the
   AC into DC. Small ceramic capacitors are normally placed across the
   diodes to reduce RF interference.
 
 One or more large filter capacitors to smooth the unregulated DC. In
   the U.S., this is most often a voltage around 150-160 V DC. In countries
   with 220 VAC power, it will typically be around 300-320 V DC.
 
 A discrete, hybrid, or IC regulator to provide stable DC to the horizontal
   deflection system. Sometimes feedback from a secondary output of the
   flyback or even the high voltage is used. This regulator may be either
   a linear or switching type. In some cases, there is no regulator.
 
 Zero or more voltage dividers and/or regulators to produce additional
   voltages directly from the line power. This relatively rare except for
   startup circuits. These voltages will not be isolated from the line.
 
 A degauss control circuit usually including a thermistor or Posistor
   (a combination of a heater disk and Positive Temperature Coefficient (PTC)
   thermistor in a single package). When power is turned on, a relatively
   high AC current is applied to the degauss coil wrapped around the periphery
   of the CRT. The PTC thermister heats up, increases in resistance, and
   smoothly decreases the current to nearly zero over a couple of seconds.
 
 A startup circuit for booting the horizontal deflection if various voltages
   to run the TV are derived from the flyback. This may be an IC or discrete
   multivibrator or something else running off a non-isolated voltage or
   the standby power supply.
 
 A standby power supply for the microcontroller and remote sensor. Usually,
   this is a separate low voltage power supply using a small power transformer
   for line isolation.
 
Always use an isolation transformer when working on a TV but this is
especially important - for your safety - when dealing with the non-isolated
line operated power supply section. Read and follow the safety guidelines.
 
8.2) Power button on set is flakey
 
If the on/off (or other button) on the set itself behaves erratically
but the remote control works fine, then it could be a dirty button or
cable or other connections to the switch PCB, particularly if the buttons
on the set itself are rarely used. There could possibly be a bad pullup
resistor or something of that sort - but is it worth the effort to locate?
 
Why not just continue to use the remote? There is no reason to suspect that
it will develop similar symptoms. However, there is some risk that if
the button is dirty, you may find the TV coming on at random times in the
middle of the night (of course!).
 
I think I have an older Sylvania that does that sort of thing - don't
really know as I never use the power button on the set!
 
If power is controlled by a hard switch - a pull or click knob, or mechanical
push-push switch and this has become erratic due to worn contacts,
replacements are available but often only directly from the original
manufacturer to physically fit and (where applicable) have the volume
or other controls built in. As an alternative, consider mounting a small
toggle switch on the side of the cabinet to substitute for the broken switch.
This will almost certainly be easier and cheaper - and quite possibly, more
reliable.
8.3) TV blows fuse
 
If the fuse really blows absolutely instantly with no indication that the
circuits are functioning (no high pitched horizontal deflection whine (if
your dog hides under the couch whenever the TV is turned on, deflection
is probably working)), then this points to a short somewhere quite near
the AC power input. The most common places would be:
 
 Degauss Posistor - very likely.
 Horizontal output transistor.
 Power supply regulator if there is one.
 Power supply chopper (switchmode) transistor if there is one.
 Diode(s) in main bridge
 Main filter capacitor(s).
 
You should be able to eliminate these one by one.
 
Unplug the degauss coil as this will show up as a low resistance.
 
First, measure across the input to the main power rectifiers - it
should not be that low. A reading of only a few ohms may mean a
shorted rectifier or two or a shorted Posistor.
 
 Test the rectifiers individually or remove and retest the resistance.
 
 Some sets use a Posistor for degauss control. This is a little cubical
  (about 1/2 x 3/4 x 1) component with 3 legs. It includes a line
  operated heater disk (which often shorts out) and a PTC thermister to
  control current to the degauss coil. Remove the posistor and try power.
  If the monitor now works, obtain a replacement but in the meantime you
  just won't have the automatic degauss.
 
If these test good, use an ohmmeter with the set unplugged to measure
the horizontal output transistor. Even better to remove it and measure it.
 
 C-E should be high in at least one direction.
 B-E may be high or around 50 ohms but should not be near 0.
 
If any readings are under 5 ohms, the transistor is bad. The parts
sources listed at the end of this document will have suitable replacements.
 
If the HOT tests bad, try powering the set first with your light bulb and if
it just flashes once when the capacitor is charging, then put a fuse in
and try it. The fuse should not blow with the transistor removed.
Of course, not much else will work either.
If it tests good, power the set without the transistor and see what happens.
If the fuse does not blow, then with the good transistor (assuming it is not
failing under load), it would mean that there is some problem with the
driving circuits possibly or with the feedback from the voltages derived
from the horizontal not regulating properly.
Look inside the TV and see if you can locate any other large power transistors
in metal (TO3) cans or plastic (TOP3) cases. There may be a separate
transistor that does the low voltage regulation or a separate regulator
IC. Some TVs have a switchmode power supply that runs off a different
transistor than the HOT. There is a chance that one of these may be bad.
If it is a simple transistor, the same ohmmeter check should be performed.
If none of this proves fruitful, it may be time to try to locate a schematic.
A blown fuse is a very common type of fault due to poor design very often
triggered by power surges due to outages or lightening storms. However,
the most likely parts to short are easily tested, usually in-circuit, with
an ohmmeter and then easily removed to confirm.
If you find the problem and repair it yourself, the cost is likely to
be under $25.
8.4) Internal fuse blew during lightening storm (or elephant hit power pole)
 
Power surges or nearby lightening strikes can destroy electronic equipment.
However, most of the time, damage is minimal or at least easily repaired.
With a direct hit, you may not recognize what is left of it!
 
Ideally, electronic equipment should be unplugged
(both AC line and phone line!)
during electrical storms if possible. Modern TVs, VCRs, microwave
ovens, and even stereo equipment is particularly susceptible to lightening and
surge damage because some parts of the circuitry are always alive and therefore
have a connection to the AC line. Telephones, modems, and faxes are directly
connected to the phone lines. Better designs include filtering and surge
suppression components built in. With a near-miss, the only thing that may
happen is for the internal fuse to blow or for the microcontroller to go
bonkers and just require power cycling. There is no possible protection
against a direct strike. However, devices with power switches that totally
break the line connection are more robust since it takes much more voltage
to jump the gap in the switch than to fry electronic parts. Monitors and
TVs may also have their CRTs magnetized due to the electromagnetic fields
associated with a lightening strike - similar but on a smaller scale to
the EMP of a nuclear detonation.
 
Was the TV operating or on standby at the time? If it was switched
off using an actual power switch (not a logic pushbutton or the remote
control), then either a component in front of the switch has blown, the
surge was enough to jump the gap between the switch contacts, or it was
just a coincidence (yeh, right).
 
If the TV was operating or on standby or has no actual power switch, then
a number of parts could be fried.
 
TVs usually have their own internal surge protection devices like MOVs (Metal
Oxide Varistors) after the fuse. So it is possible that all that is wrong is
that the line fuse has blown. Remove the cover (unplug it first!) and start
at the line cord. If you find a blown fuse, remove it and measure across
the in-board side of fuse holder and the other (should be the neutral) side
of the line. The ohmmeter reading should be fairly high - well certainly not
less than 100 ohms - in at least one direction. You may need to unplug the
degaussing coil to get a reasonable reading as its resistance may be 25 or 30
ohms. If the reading is really low, there are other problems. If the
resistance checks out, replace the fuse and try powering the TV. There will
be 3 possibilities:
 
 It will work fine, problem solved.
 
 It will immediately blow the fuse. This means there is at least one
   component shorted - possibilities include an MOV, line rectifiers, main
   filter cap, regulator transistor, horizontal output transistor, etc. You
   will need to check with your ohmmeter for shorted semiconductors. Remove
   any that are suspect and see of the fuse now survives (use the series
   light bulb to cut your losses - see the section:
The series light bulb trick.
 
 It will not work properly or appear dead. This could mean there are
   open fusable resistors other defective parts in the power supply or
   elsewhere. In this case further testing will be required and at some
   point you may need the schematic.
If the reading is very low or the fuse blows again, see the section:
TV blows fuse.
8.5) Fuse replaced but TV clicks with power-on but no other action
 
The click probably means that the power relay is working, though there could
be bad contacts.
 
Since the fuse doesn't blow now (you did replace it with one of the same
ratings, right?), you need to check for:
 
 Other blown fuses - occasionally there are more than one in a TV.
Replace with one of exactly the same ratings.
 
 Open fusable resistors. These sometimes blow at the same time or in
  place of the fuses. They are usually low values like 2 ohms and are in
  big rectangular ceramic power resistor cases or smaller blue or gray
  colored cylindrical power resistors. They are supposed to protect
  expensive parts like the HOT but often blow at the same time.
If any of these are bad, they will need to be replaced with flameproof
resistors of the same ratings (though you can substitute an ordinary
resistor for testing purposes). Before applying power, check (for shorts):
Rectifier diodes
Horizontal Output Transistor (HOT)
Regulator pass or chopper transistor (if present)
Main filter capacitor
 
An initial test with an ohmmeter can be done while in-circuit. The
resistance across each diode and the collector to emitter of the
transistors should be relatively high - a few hundred ohms at lest -
in at least one direction (in-circuit). If there is a question, unsolder
one side of each diode and check - should be in the Megohms or higher in
one direction. Removed from the circuit, the collector-emitter resistance
should be very high in one direction at least. Depending on the type,
the base-emitter resistance may be high in one direction or around 50 ohms.
If any reading on a semiconductor device is under 10 ohms - then the device
most likely bad. Assuming that you do not have a schematic, you should
be able to locate the rectifiers near where the line cord is connected and
trace the circuit. The transistors will be either in a TO3 large metal can
or a TOP3 plastic package - on heat sinks. The filter capacitor should
eventually measure high in one direction (it will take a while to charge
from your ohmmeter). It could still be failing at full voltage, however.
 
If you find one bad part, still check everything else as more than one part
may fail and just replacing one may cause it to fail again.
 
Assuming everything here checks out, clip a voltmeter set on its 500 V scale
or higher across the horizontal output transistor and turn the power on.
Warning - never measure this point if the horizontal deflection is operating.
it is ok now since the set is dead. If the voltage here is 100-150, then
there is a problem in the drive to the horizontal output circuit. If it
is low or 0, then there are still problems in the power supply or with the
winding on the flyback transformer.
 
Other possible problems:
Bad hybrid voltage regulator
bad startup circuit
Bad relay contacts as mentioned above.
8.6) Power-on tick-tick-tick or click-click-click but no other action
 
A variety of power supply or startup problems can result in this or
similar behavior. Possibilities include:
 
 Lack of startup horizontal drive - see the section:
Startup problems.
  The main regulator is cycling on overvoltage due to lack of load.
 
 Excessive load or faulty power supply cycling on its overcurrent
  protection circuit.
 
 HV shutdown, or some other system detecting an out of regulation condition.
  However, in this case, there should be some indication that the deflection
  and HV is attempting to come up - momentary whine, static on the screen, etc.
 
 A dried up main filter capacitor or other filter capacitor in the low
  voltage power supply that is producing an out-of-regulation condition
  until it warms up. A bad filter capacitor on the output of a series
  regulator may result in excessive voltage and subsequent shutdown.
 
 A problem with the microcontroller, relay or its driver, or standby power supply.
One possible test would be to vary the line voltage and observe the
set's behavior. It may work fine at one extreme (usually low) or the
other. This might give clues as to what is wrong.
 
Also see the section:
Dead TV with periodic tweet-tweet-tweet or flub-flub-flub.
 
8.7) No picture or raster and no sound
 
The screen is blank with no raster at all. There are indications that the
channel numbers are changing in the display. This indicates that some
of the low voltages are present but these may be derived from the standby
supply.
 
Assuming there is no deflection and no HV, you either have a low
voltage power supply problem, bad startup circuit, or bad horizontal
output transistor (HOT)/bad parts in the horizontal deflection.
 
Check for bad fuses.
 
(If you have HV as indicated by static electricity on the front of the
screen and you hear the high pitched whine of the horizontal deflection
when it is turned on, then the following does not apply).
 
 Use an ohmmeter to test the HOT for shorts. If it is bad, look for
   open fusable resistors or other fuses you did not catch.
 
 Assuming it is good, measure the voltage on the collector-emitter
   of the HOT (this is safe if there is no deflection). You should see
   the B+ - probably between 100 and 150 V.
 
 If there is no voltage, you have a low voltage power supply problem
   and/or you have not found all the bad/open parts.
 
 If there is voltage and no deflection (no high pitched whine and no
   HV), you probably have a startup problem - all TVs need some kind of
   circuit to kick start the horizontal deflection until the auxiliary
   power outputs of the flyback are available. Some Zeniths use a simple
   multivibrator for this - a couple of transistors. Others power the
   horizontal osc. IC from a special line-derived voltage. The multivibrator
   type are sometimes designed to fail if someone keeps turning the set on
   and off (like kids playing) since the power rating is inadequate.
 
   Test the transistors if it is that type with an ohmmeter. If one is
   shorted, you have a problem. The usual way a TV service person would
   test for startup problems is to inject a signal to the base of the HOT
   of about 15.75 KHz. If the TV then starts and runs once this signal
   is removed, the diagnosis is confirmed. This is risky - you can blow
   things up if not careful (including yourself).
If you hear the high pitched whine of the deflection and/or feel some static
on the scree, confirm that the horizontal deflection and high voltage are
working by adjusting the SCREEN control (probably on the flyback). If you can
get a raster then your problem is probably in the video or chroma
circuits, not the deflection or high voltage.
 
8.8) Reduced width picture and/or hum bars in picture and/or hum in sound
 
The most likely cause is a dried up main filter capacitor. Once the
effective capacitance drops low enough, 120 Hz (or 100 Hz in countries with
50 Hz power) ripple will make its way into the regulated DC supply
(assuming full wave rectification).
 
Another likely cause of similar symptoms is a defective low voltage
regulator allowing excessive ripple. The regulator IC could be bad
or filter capacitor following the IC could be dried up.
 
Either of these faults may cause:
 
 A pair of wiggles and/or hum bars in the picture which will float up
   the screen. For NTSC where the power line is 60 Hz but the frame rate
   is 59.94 Hz, it will take about 8 seconds for each bar to pass a given
   point on the screen. (On some sets, a half wave recitifier is used
   resulting in a single wiggle or hum bar).
 
 Hum in the sound. This may or may not be noticeable with the volume
   turned down.
 
 Possible regulation problems resulting in HV or total shutdown or power
   cycling on and off.
The best approach to testing the capacitors is to clip a good capacitor of
approximately the same uF rating and at least the same voltage rating across
the suspect capacitor (with the power off). A capacitor meter can also
be used but the capacitor may need to be removed from the circuit.
 
Once the capacitors have been confirmed to be good, voltage measurements
on the regulator should be able to narrow down the problem to a bad IC
or other component.
 
8.9) TV power cycling on and off
 
The power light may be flashing or if you are runing with a series
light bulb it may be cycling on and off continuously. There may be
a chirping or clicking sound from inside the set.
(NOTE: using too small a light bulb for the size of the TV
may also result in this condition.)
 
If there is a low voltage regulator or separate switching supply, it
could be cycling on and off if the horizontal output, flyback, or
one of its secondary loads were defective.
 
Does this TV have a separate low voltage regulator and/or switching power
supply or is it all part of the flyback circuit? For the following, I assume
it is all in one (most common).
 
Some simple things to try first:
 
Verify that the main filter capacitor is doing its job. Excessive ripple
on the rectified line voltage bus can cause various forms of shutdown
behavior. An easy test is to jumper across the capacitor with one of
at least equal voltage rating and similar capacitance
(make connections with power off!).
 
Use a Variac, if possible, to bring up the input voltage slowly and see if
the TV works at any point without shutting down. If it does, this could be
an indication of X-ray protection circuit kicking in, though this will
usually latch and keep the set shut off if excessive HV were detected.
 
8.10) Dead TV with periodic tweet-tweet-tweet or flub-flub-flub
 
A TV which appears to be dead except for a once a second or so
tweet or flub usually indicates an overload fault in the power supply
has a short in one of its load circuits, very often a shorted
rectifier. It could also be the flyback, but check the the loads first.
Wait a few minutes for the filter caps to discharge (but stay away from the
CRT HV connector as it may retain a dangerous and painful charge for a long
time), use an ohmmeter across the various diodes in the power supply.
Using an ohmmeter on the rectifier diodes, the resistance
in at least one direction should be greater than 100 ohms.
If it is much less (like 0 or 5 ohms), then the diode is probably bad.
Unsolder and check again - it should test infinite (greater than 1M ohms)
in one direction.
 
Other possible causes:
 
 Bad solder connections.
 Other shorted components like capacitors.
 Other problems in the power supply.
 Bad flyback.
 Short or excessive load on secondary supplies fed from flyback.
 Problem with startup drive (cycling on overvoltage).
8.11) Shorted Components
 
A failure of the horizontal output transistor or power supply switchmode
transistor will blow a fuse or fusable resistor.
 
Look for blown fuses and test for open fusable resistors in the power circuits.
If you find one, then test the HOT and/or switchmode transistor for shorts.
 
Other possibilities: rectifier diodes or main filter capacitor.
 
While you are at it, check for bad connections - prod the circuit board with an
insulated stick when the problem reoccurs - as these can cause parts to
fail.
 
8.12) Startup problems - nothing happens, click, or tick-tick-tick sound
 
TVs and monitors usually incorporate some kind of startup circuit to provide
drive to the horizontal output transistor (HOT) until the flyback power supply
is running. Yes, TVs and monitors boot just like computers.
 
There are two typical kinds of symptoms: power on click but nothing else
happens or a tick-tick-tick sound indicating cycling of the low voltage
(line regulator) but lack of startup horizontal drive.
 
Check the voltage on the horizontal output transistor (HOT). If no voltage
is present, there may be a blown fuse or open fusable resistor - and
probably a shorted HOT.
 
However, if the voltage is normal (or high) - usually 100-150 V, then
there is likely a problem with the startup circuit not providing initial
base drive to the HOT.
 
The startup circuits may take several forms:
 
 Discrete multivibrator or other simple transistor circuit to provide
   base drive to the HOT.
 
 IC which is part of deflection chain powered off of a voltage divider
   or transformer.
 
 Other type of circuit which operates off of the line which provides
   some kind of drive to the HOT.
 The startup circuit may operate off of the standby power supply or
voltage derived from non-isolated input. Be careful - of course, use
an isolation transformer whenever working on TVs and especially for power
supply problems.
 
Note that one common way of verifying that this is a startup problem is
to inject a 15 KHz signal directly into the HOT base or driver circuit
(just for a second or two). If the TV then starts up and continues to run,
you know that it is a startup problem.
 
CAUTION: Be careful if you do this. The HOT circuit may be line-connected
and it is possible to destroy the HOT and related components if this is not
done properly. I once managed to kill not only the HOT but the chopper
transistor as well while working in this area. An expensive lesson.
 
I have also seen startup circuits that were designed to fail. Turning
the TV on and off multiple times would exceed the power ratings of the
components in the startup circuit. Some Zenith models have this 'feature'.
 
When this situation exists, it could be that the circuit is not providing
the proper drive or that due to some other circuit condition, the drive
is not always sufficient to get the secondary supplies going to the point
that the normal circuits take over.
 
I would still check for bad connections - prod the circuit board with an
insulated stick when the problem reoccurs
 8.13) TV turns off after warming up
If you can turn it back on with the s momentary key or power button:
When it shuts off, do you need to push the power button once or twice
to get it back on? Also, does anything else about the picture or sound
change as it warms up?
 If once, then the controller is shutting the TV down either as a result of
   a (thermally induced) fault in the controller or it sensing some other
   problem. Monitoring the voltage on the relay coil (assuming these
   is one) could help determine what is happening. The controller thinks
   it is in charge.
 
 If twice, then the power supply is shutting down as the controller still
   thinks it is on and you are resetting it. A couple of possibilities
   here would be low voltage or high voltage regulation error (excessive
   high voltage is sensed and causes shutdown to prevent dangerous X-ray
   emission). A partially dried up main filter capacitor could also cause a
   shutdown but there might be other symptoms like hum bars in the picture just
   before this happened. Clipping a good capacitor across the suspect
   (with power off!) would confirm or eliminate this possibility.
 
If it uses a pull-knob (or other hard on/off switch), then this may be like
pulling the plug and would reset any abnormal condition.
8.14) TV doesn't power up immediately
 
The TV may do nothing, cycle on and off for a while, power up and then
shutdown in an endless cycle - or at least for a while. Then it comes
on and operates normally until it is turned off.
 
A couple of possibilities:
 
 The main filter capacitor or other filter capacitors in the low voltage
   power supply is dried up and this can cause all kinds of regulation
   problems.
 
 The power supply regulator is defective (or marginal) allowing excessive
   voltage on its output and then the X-ray protection circuitry shuts
   you down.
If you can get access to a Variac, it would be worth bringing up the input
voltage slowly and seeing if there is some point at which it would stay on.
 
If there is, then if the picture has serious hum bars in it the main filter
cap could be bad. If more or less a decent picture with minor hum bars then
it could be the regulator.
 
8.15) Old TV requires warmup period
 
So, what else is new? In the old days, a TV was expected to take a few
minutes (at least) to warm up. We are all spoiled today. Of course, you
usually maintained a full time technician or engineer to fiddle with the
convergence adjustments!
 
A TV (from around 1983) needs at least 5 min. to warm up (lighting up the
screen and making sound if I give it a cold start. Once warmed up, you
can it off and on again from the front panel and it will work immediately.
Another thing this TV has a sub-power switch in the rear.
 
1983 sounds a bit late, but sets in the late '70 during the transition from
tubes to all solid state chassis often had the 'sub-power' switch providing
some power to the filaments of the CRT and other tubes - usually in the
deflection and high voltage circuits since these would take a while to heat up
and stabilize. The idea was to leave this switch on all the time (except when
going on vacation - it was sometimes labeled 'vacation') so that you would
have nearly instant warm up. Supposedly, this led to an increased risk of
fire as well (see the section:
About instant on TVs).
 
If it is a totally solid state chassis, then there is some component - probably
a capacitor in the power supply since it affects both picture and sound - that
is drifting with temperature and needs to be located with cold spray or a
heat gun.
 
8.16) Relays in the Power Circuitry of TVs
 
What exactly is the purpose of such a relay ... i.e., why doesn't the
power switch on the TV just apply power directly instead of through a
relay?
 
The usual reason for a relay instead of a knob switch is to permit a remote
control to turn power on and off. If your TV does not have a remote, then
it is simply the same chassis minus 24 cents worth of circuitry to do the
remote function. Isn't marketing wonderful?
The only unknown is the coil voltage. It is probably somewhere in
the 6-12 volt range. You should be able to measure this on the coil
terminals in operation. It will be a DC coil.
However, the relay controls the 125 VAC (or 220) which you should treat
with respect - it is a lot more dangerous than the 25KV+ on the CRT!
 
Almost certainly, the relay will have 4 connections - 2 for power and 2
for the coil. If it is not marked then, it should be pretty easy to
locate the power connection. One end will go to stuff near the AC line
and the other end will go to the rectifier or maybe a fusable resistor
or something like that. These will likely be beefier than the coil
connections which will go between a transistor and GND or some low voltage,
or maybe directly into a big microcontroller chip.
 
Of course, the best thing would be to get the schematic. Some big public
libraries carry the SAMs photofact series for TVs and VCRs. If not, take
10 minutes and trace it. You should be able to get far enough to determine
the relay connections.
 
Once you are sure of the AC connections - measure across them while it is
off and also while it is on. While off, you should get 110-125 VAC.
While on and working - 0. While on and not working either 110-125 VAC
if the relay is not pulling in or 0 if it is and the problem is elsewhere.
We can deal with the latter case if needed later on. Note the even if the
relay contacts are not working, the problem could still be in the control
circuitry not providing the correct coil voltage/current, though not likely.
 
It may be expensive and/or difficult to obtain an exact replacement, but
these are pretty vanilla flavored as relays go. Any good electronics
distributor should be able to supply a suitable electrical replacement
though you may need to be creative in mounting it.
 
8.17) Flameproof Resistors
 
Flameproof Resistor or Fusable Resistor are often designated by the
symbol 'FR'. They are the same.
 
You may see these in the switchmode power supplies used in TVs and monitors.
They will look like power resistors but will be colored blue or gray, or may
be rectangular ceramic blocks. They should only be replaced with flameproof
resistors with identical ratings. They serve a very important safety function.
 
These usually serve as fuses in addition to any other fuses that may be
present (and in addition to their function as a resistor, though this isn't
always needed). Since your FR has blown, you probably have shorted
semiconductors that will need to be replaced as well. I would check
all the transistors and diodes in the power supply with an ohmmeter.
You may find that the main switch mode transistor has decided to turn into
a blob of solder - dead short. Check everything out even if you find one
bad part - many components can fail or cause other components to fail
if you don't locate them all. Check resistors as well, even if they look ok.
 
Then, with a load on the output of the power supply use a Variac to bring
up the voltage slowly and observe what happens. At 50 VAC or less, the
switcher should kick in and produce some output though correct regulation
may not occur until 80 VAC or more. The outputs voltages may even be
greater than spec'd with a small load before regulation is correct.
 
Chapter 9) Deflection Problems
9.1) Deflection fundamentals
 
The electron beams in the CRT need to be scanned horizontally and vertically
in a very precise manner to produce a raster - and a picture.
 
For NTSC and PAL, the horizontal scan rates are 15,734 and 15,625 Hz
respectively.
 
For NTSC and PAL, the vertical scan rates are 60 and 50 Hz (approximately)
respectively.
 
The deflection yoke includes sets of coils for horizontal and vertical
scanning oriented at 90 degrees with respect to each other. Additional
coils are needed to correct for pincushion and other geometric defects.
 
The deflection circuits must be synchronized and phase locked to the
incoming video signal.
 
Therefore, we have the following functions:
 
 Sync separator to obtain horizontal and vertical synchronization pulses.
 
 Horizontal oscillator which locks to horizontal sync pulses.
 
 Horizontal drive followed by horizontal output which feeds deflection
   yoke (and flyback for HV and other voltages), Yoke requires a sawtooth
   current waveform for linear horizontal deflection. Horizontal output
   in all but the smaller TVs is a large discrete power transistor, most
   often an NPN bipolar type.
 
 Vertical oscillator which locks to vertical sync pulses. Yoke requires
   sawtooth waveform for linear vertical deflection.
 
 Vertical drive/output which feeds vertical deflection yoke. Newer TVs
   use ICs for vertical drive and output.
 
 Various additional deflection signals to correct for the imperfections
   in the geometry of large angle deflection CRTs. These may be fed into
   the normal deflection coils and/or there may be separate coils mounted
   on the neck of the CRT.
9.2) Why are nearly all horizontal drivers circuits transformer coupled?
 
One (probably secondary) reason is that this provides one of the
isolation barriers between a line-connected HOT and flyback primary
and the signal circuits of the TV.
 
A more important rational is that a transformer is nice easy way of
impedance matching the horizontal driver circuit (100s to 1000s of ohms)
to the few ohm input impedance of the horizontal output transistor
base which requires upwards of several amps for proper drive. A typical
driver transformer may be in the 5-10:1 turns ratio representing 25-100:1
impedance ratio.
 
A byproduct of all this is that it is almost impossible for a faulty
driver stage to kill the HOT.
 
9.3) Picture squeezed in then died
 
You were watching 'Knight Rider' reruns and all of a sudden, the picture
squeezed in slowly from the right hand side. It squeezed in about 2
inches or so when the entire picture went dead - has remained like this since.
Sound is fine, but no activity at all from the tube. Has it died? How
much time, effort, and expense to fix?
 
No, it's not dead, at least it certainly is not the picture tube.
 
Your set probably didn't like Knight Rider - at least that episode!
 
Seriously, how old is the set? Is it a totally solid state chassis or
are there tubes in the deflection circuits?
 
Is there any indication of light on the screen? Any indication of the 15735 Hz
horizontal running at all? (You would normally hear the high pitch sound).
 
Newer TVs almost always derive voltages for the sound circuits from the
horizontal deflection but older hybrids may run the sound off of its own
power.
 
In any case, there is a problem in the horizontal deflection and you probably
have no high voltage as well assuming no light on the screen.
 
The fact that it squeezed in first indicates that a partial short or other
fault may have developed in the horizontal deflection circuits - possibly
the deflection yoke or flyback transformer. It could also have been a bad
connection letting loose. Once it failed completely, the horizontal output
transistor may have bought the farm or blown a fuse.
 
9.4) Horizontal deflection shutting down
 
Confirm that the horizontal deflection is shutting down (along with the
high voltage since it is derived from horizontal deflection: listen
for the high pitched deflection whine, test for static on the screen,
see if the CRT filaments are lit, turn up the brightness and/or screen
control to see if you can get a raster) and then why:
 
 Power is failing to the horizontal output transistor - this could be
   due to a low voltage power supply problem, bad connection, etc.
 
 Base drive to the horizontal output transistor is failing - could be a
   fault in the horizontal oscillator or bad connection.
 
 Problem with the flyback transformer or its secondary loads (flyback
   may provide other power voltages).
 
 X-ray protection is activating - either due to excess HV or due to a
   fault in the X-ray protection circuitry.
 
If the problem comes and goes erratically it sounds like a bad connection,
especially if whacking has an effect. If it comes and goes periodically,
then a component could be heating up and failing, then cooling, etc.
 
9.5) Horizontal lock lost
 
A TV which loses horizontal lock when changing channels, momentarily
losing the signal, or switching inputs may have a horizontal oscillator
that is way out of adjustment or has drifted in frequency due to aging
components.
 
Note that the characteristics of this are distinctly different than
for total loss of sync. In the latter case, the picture will drift sideways
and/or up and down while with an off frequency oscillator, the torn up
picture will try at least to remain stationary.
 
This could be a capacitor or other similar part. Or, the oscillator
frequency may just need to be tweaked (particularly with older sets).
There may be an internal horizontal frequency adjustment - either a pot
or a coil - which may need a slight tweak. If a coil, use a plastic
alignment tool, not metal to avoid cracking the fragile core.
 
A schematic will be useful to locate the adjustment if any or to identify
possible defective parts. Try a large public library for the SAMs Photofact
for this set.
 
9.6) Vertical squashed
 
This is a vertical deflection problem - possibly a bad capacitor, bad
connection, or other component. None of these should be very expensive
(in a relative sort of way).
 
Start by substituting a good capacitor for each electrolytic in the
vertical output circuit. Look for bad connections (particularly to the
deflection yoke), then consider replacing the vertical output IC or
transistor(s).
 
The following are NOT possible: CRT, flyback, tuner. (I am just trying to
think of really expensive parts that cannot possibly be at fault).
 
Note that some movies or laser karaoke discs are recorded in 'letterbox'
format which at first glance looks like a squashed vertical problem. However,
the picture aspect ratio will be correct and turning up the brightness will
reveal a perfectly normal raster above and below the picture.
 
9.7) Part of picture cut off
 
The following applies if the part of the picture is missing but not
otherwise squashed or distorted. For example, 85% is missing but the
portion still visible is normal size.
 
Wow! That's an interesting one, more so than the typical run-of-the-mill
my TV just up and died on me.
Or, my pet orangutan just put a hole in the CRT, what should I do?
 
Since the size of the picture fragment is correct but 85% is missing,
my first thought would be to check waveforms going into the vertical
output stage. The supply voltage is probably correct since that often
determines the size. It almost sounds like the waveform rather than
being mostly on (active video) and off for the short blanking period
is somehow only on during the last part of the active video thus giving
you just the bottom of the picture. If there is a vertical output IC,
it may be defective or the blanking input to it may be corrupted. The
problem may be as far back as the sync separator. Then again who knows,
maybe wait for the schematics.
 
9.8) Single Vertical Line
 
Since you have high voltage, the horizontal deflection circuits are almost
certainly working (unless there is a separate high voltage power supply -
almost unheard of in modern TVs and very uncommon in all but the most
expensive monitors).
 
Check for bad solder connections between the main board and the deflection
yoke. Could also be a bad horizontal coil in the yoke, linearity coil, etc.
There is not that much to go bad based on these symptoms assuming the high
voltage and the horizontal deflection use the same flyback. It is almost
certainly not an IC or transistor that is bad.
 
9.9) Single Horizontal Line
 
A single horizontal line means that you have lost vertical deflection.
High voltage is most likely fine since there is something on the screen.
 
This could be due to:
 Dirty service switch contacts. There is often a small switch on the
   located inside on the main board or perhaps accessible from the back. This
   is used during setup to set the color background levels. When flipped
   to the 'service' position, it kills vertical deflection and video to the
   CRT. If the switch somehow changed position or got dirty or corroded
   contacts, you will have this symptom. Flip the switch back and forth
   a couple of times. If there is some change, then replace, clean, resolder,
   or even bypass it as appropriate.
 
 Bad connection to deflection yoke or other parts in vertical output
   circuit. Bad connections are common in TVs and monitors. Check
   around the pins of large components like transformers, power transistors
   and resistors, or connectors for hairline cracks in the solder. Reseat
   internal connectors. Check particularly around the connector to the
   deflection yoke on the CRT.
 
 Bad vertical deflection IC or transistor. You will probably need
   the service manual for this and the following. However, if the
   vertical deflection is done with an IC, the ECG Semiconductor
   Master Substitution guide may have its pinout which may be enough to
   test it with a scope.
 
 Other bad parts in vertical deflection circuit though there are not
   that many parts that would kill the deflection entirely.
 
 Loss of power to vertical deflection circuits. Check for blown
   fusable resistors/fuses and bad connections.
 
 Loss of vertical oscillator or vertical drive signals.
The most likely possibilities are in the deflection output stage or
bad connections to the yoke.
 
9.10) Loss of Horizontal Sync (also applies to vertical) after Warmup
 
The problem lies either in the horizontal oscillator or in the sync system.
If it really is a problem with sync pulses not reaching the oscillator,
the picture will move around horizontally and can be brought to hold
momentarily with the hold control. If the picture breaks up into strips,
there is a problem in the horizontal oscillator. Rotate the hold control:
if the frequency is too far off, the picture will not settle into place
at any adjustment of the hold control. Look around the horizontal oscillator
circuit: all of the oscillator parts will be right there, or check on
the horizontal oscillator module. Another horizontal problem can occur
if the set is an RCA made from around 1972-1980: these sets are designed
to slip very far off sync if the high voltage is too high, to protect
against radiation. Turning up the brightness will decrease the number
of bars if this system is in question, as the high voltage is decreasing.
In this case, check around the high-voltage regulation system on the
deflection systems board. I've had 2 1970's RCA's with this problem.
(C.P.H.).
 
9.11) Intermittent jumping or jittering of picture or other random behavior
This has all the classic symptoms of a loose connection internal to the
TV or monitor - probably where the deflection yoke plugs into the main PCB or
at the base of the flyback transformer. TVs and monitors are notorious for
both poor quality soldering and bad connections near high wattage components
which just develop over time from temperature cycling.
 
The following is not very scientific, but it works: Have you tried whacking
the TV when this happened and did it have any effect? If yes, this would
be further confirmation of loose connections.
 
What you need to do is examine the solder connections on the PCBs in the
monitor, particularly in the area of the deflection circuits and power supply.
Look for hairline cracks between the solder and the component pins - mostly
the fat pins of transformers, connectors, and high wattage resistors. Any
that are found will need to be reflowed with a medium wattage (like 40W) or
temperature controlled soldering iron.
 
It could also be a component momentarily breaking down in the power supply
or deflection circuits.
 
One other possibility is that there is arcing or corona as a result of humid
weather. This could trigger the power supply to shut down perhaps
with a squeak, but there would probably be additional symptoms including
possibly partial loss of brightness or focus before it shut down. You may
also hear a sizzling sound accompanied by noise or snow in the picture,
static in the sounds, and/or a smell of ozone.
 
9.12) Horizontal output transistors keep blowing
 
Unfortunately, these sorts of problems are often difficult to definitively
diagnose and repair - with expensive component swapping.
 
You have just replaced an obviously blown (shorted) horizontal output
transistor and an hour later, same symptoms:
 
Did the new transistor short?
 
Would the next logical step be a new flyback (LOPT)? Not necessarily.
 
If the set performed normally until it died, there are other possible
causes. However, it could be the flyback failing under load or when it
warms up. I would expect some warning though - like the picture shrinks
for a few seconds before the poof.
 
Other possible causes:
 
 Insufficient drive to horizontal output transistor (HOT). A weak drive
   would cause the HOT to either turn on or shut off too slowly greatly
   increasing heat dissipation. Check driver and HOT base circuit components.
 
 Excessive voltage on HOT collector - check LV regulator (and line
   voltage if this is a field repair), if any.
 
 Defective safety capacitors or damper diode around HOT. (Though
   this usually results in instant destruction with little heating).
 
 New transistor not mounted properly to heat sink - probably needs mica
   washer and heat sink compound.
 
 Replacement transistor not correct or inferior cross reference.
   Sometimes, the horizontal deflection is designed based on the quirks
   of a particular transistor. Substitutes may not work reliably.
The HOT should not run hot - properly mounted to the heat sink,
it should not be too hot to touch (CAREFUL - don't touch with power on -
it is at over a hundred volts with nasty multihundred volt spikes and line
connected - discharge power supply filter caps first after
unplugging). If it is scorching hot after a few minutes, then you
need to check the other possibilities.
 
It is also possible that a defective flyback - perhaps one shorted turn - would
not cause an immediate failure and only affect the picture slightly. This
would be unusual, however. See the section: Testing of flyback (LOPT)
transformers.
 
Note that running the set with a series light bulb may allow the HOT
to survive long enough for you to gather some of the information needed
to identify the bad component.
 
9.13) Vertical foldover
 
The picture is squashed vertically and a part of it may be flipped over and
distorted.
 
This usually indicates a fault in the vertical output circuit. If it uses
an IC for this, then the chip could be bad. It could also be a bad capacitor
or other component in this circuit. It is probably caused by a fault in
the flyback portion of the vertical deflection circuit - a charge pump that
generates a high voltage spike to return the beam to the top of the screen.
 
Test components in the vertical output stage or substitute for good ones.
9.14) Squashed picture on late model GE, RCA, or ProScan TV
 
(From: dcavs@aol.com (DCAVS)
 
Symptoms are a picture that is as wide as the screen but the vertical
height is compressed. Picture starts about 1/3 of the way down the tube and
extends to about 1/3 of the way up from the bottom. Furthermore, the
bottom traces seem to be overlayed resulting in brighter than normal lines.
 
This is a common problem for all GE, RCA, ProScan televisions of a
variety of chassis. It is due to a design and manufacturing flaw.
You should call RCA Customer Relations at 317-587-4151
and take it to a Thompson Authorized Servicenter. (Thompson Electronics
of France owns the names, RCA, GE, and ProScan for Televisions.)
Thompson has been sending their customers $75.00 for carry in service
and $95.00 for in-home service. This amount should cover the bill as any
technician who knows what they are doing should be able to complete
the repairs quickly. There is a small chance that the data in the e-prom
IC that stores all the setup data has become corrupted. In this case the
set needs to be re-programmed to operate correctly. This is a time
consuming process and can have a great affect on the quality of reception.
 
9.15) Pincushioning Problems
 
If the left and right sides of the picture are bowed and the screen
looks something like the following (or the opposite - barrel distortion:
 
 ============================================
 \ /
  \ /
   \ /
    \ /
     \ /
      \ /
       | |
       | |
       | |
      / \
     / \
    / \
   / \
  / \
 / \
==============================================
Examine closely your electrolytic caps on the mother board for leaky ones.
Also look into your horz. circuitry to make sure signals and voltages are
correct. (Gary)
 
In particular, this sounds like a pincushion problem - to correct for
pincushion, a signal from the vertical deflection that looks something
like a rectified sinewave is used to modify width based on vertical position.
There is usually a control to adjust the magnitude of this signal and also
often, its phase. It would seem that this circuit has ceased to function.
If you have the schematics, check them for 'pincushion' adjustments and
check signals and voltages. If not, try to find the 'pincushion' magnitude
and phase adjustments and look for bad parts or bad connections in in the
general area. Even if there are no adjustment pots, there may still be
pincushion correction circuitry.
 
If the internal controls have absolutely no effect, then the circuit
is faulty. With modern digital setup adjustments, then it is even tougher
to diagnose since these control a D/A somewhere linked via a microprocessor.
 
Pincushion adjustment adds a signal to the horizontal deflection
to compensate for the geometry of the CRT/deflection yoke. If you have
knobs, then tracing the circuitry may be possible. With luck, you have
a bad part that can be identified with an ohmmeter - shorted or open.
However, without a schematic even this will be difficult. If the adjustments
are digital this is especially difficult to diagnose since you don't even
have any idea of where the circuitry would be located.
 
Faulty capacitors in the horizontal deflection power supplies often cause
a similar set of symptoms.
 
9.16) Testing of flyback (LOPT) transformers
 
How and why do flyback transformers fail?
 
Flybacks fail in several ways:
 Overheating leading to cracks in the plastic and external arcing. These
   can often be fixed by cleaning and coating with multiple layers of high
   voltage sealer, corona dope, or even plastic electrical tape (as a
   temporary repair in a pinch).
 
 Cracked or otherwise damaged core will effect the flyback characteristics
   to the point where it may not work correctly or even blow the horizontal
   output transistor.
 
 Internal shorts in the FOCUS/SCREEN divider network, if present. One sign
   of this may be arcover of the FOCUS or SCREEN sparkgaps on the PCB on the
   neck of the CRT.
 
 Internal short circuits in the windings.
 
 Open windings.
More than one of these may apply in any given case.
 
First, perform a careful visual inspection with power off. Look for cracks,
bulging or melted plastic, and discoloration, Look for bad solder connections
at the pins of the flyback as well. If the TV or monitor can be powered
safely, check for arcing or corona around the flyback and in its vicinity,
 
Next, perform ohmmeter tests for obvious short circuits between windings,
much reduced winding resistances, and open windings.
 
For the low voltage windings, service manuals may provide the expected
DC resistance (SAMs PhotoFact, for example). Sometimes, this will change
enough to be detected - if you have an ohmmeter with a low enough scale.
These are usually a fraction of an ohm. It is difficult or impossible to
measure the DC resistance of the HV winding since the rectifiers are usually
built in. The value is not published either.
 
CAUTION: make sure you have the TV or monitor unplugged and confirm that
the main filter capacitor is discharged before touching anything! If you
are going to remove or touch the CRT HV, focus, or screen wires, discharge
the HV first using a well insulated high value resistor (e.g., several
M ohms, 5 W) to the CRT ground strap (NOT signal ground. See the section:
Safe discharging of capacitors in TVs and video monitors.
 
Partially short circuited windings (perhaps, just a couple of turns)
and sometimes shorts in the focus/screen divider will drastically lower
the Q and increase the load the flyback puts on its driving source with
no outputs connected. Commercial flyback testers measure the Q by
monitoring the decay time of a resonant circuit formed by a capacitor and
a winding on the flyback under test after it is excited by a pulse
waveform. It is possible to easily construct testers that perform a
well. See the companion document
Testing of Flyback (LOPT) Transformers for further information.
 
Chapter 10) High Voltage Power Supply Problems
 
10.1) HV power supply fundamentals
 
Most, if not all, TVs derive the high voltage for the CRT second anode,
focus, and (sometimes) screen (G2) from the horizontal deflection system.
This technique was developed quite early in the history of commercial TV
and has stuck for a very simple reason - it is very cost effective. A
side effect is that if the horizontal deflection fails and threatens to
burn a (vertical) line into the CRT phosphors, the high voltage dies as well.
 
Most TV high voltage supplies operate as follows:
 
 Horizontal output transistor (HOT) turns on during scan. Current increases
   linearly in primary of flyback transformer since it appears as an
   inductor. Magnetic field also increases linearly. NOTE: flyback is
   constructed with air gap in core. This makes it behave more like an
   inductor as far as the primary drive is concerned.
 
 HOT shuts off at end of scan. Current decreases rapidly. Magnetic field
   collapses inductively coupling to secondary and generates HV pulse.
   Inductance and capacitance of flyback, snubber capacitors, and parasitic
   capacitance of circuitry and yoke form a resonant circuit. Ideally,
   voltage waveform across HOT during flyback (retrace) period will be a
   single half cycle and is clamped by damper diode across HOT to prevent
   undershoot.
 
 Secondary of flyback is either a single large HV winding with HV rectifiers
   built in (most often) or an intermediate voltage winding and a voltage
   multiplier (see the section: What is a tripler.) The output will be
   DC HV pulses.
 
 The capacitance of the CRT envelope provides the needed filtering to
   adequately smooth the HV pulses into a DC voltage.
 
 A high resistance voltage divider provides the several KV focus voltage
   and sometimes the several hundred volt screen (G2) voltage as well.
   Often, the adjustments for these voltages are built into the flyback.
   Sometimes they are mounted separately.
10.2) What is a tripler?
 
In some TVs, the flyback transformer only generates about 6-10 KV AC which
is then boosted by a capacitor-diode ladder to the 18-30 KV needed for modern
color CRTs. The unit that does this is commonly called a tripler since it
multiplies the flyback output by about 3 times. Some TVs use a quadrupler
instead. However, many TVs generate the required HV directly with a winding
with the required number of turns inside the flyback transformer.
 
Triplers use a diode-capacitor ladder to multiply the 6-10 KV AC to 18-30 KV
DC. Many triplers are separate units, roughly cubical, and are not repairable.
Some triplers are built in to the flyback - it is probably cheaper to
manufacture the HV diodes and capacitors than to wind a direct high voltage
secondary on the flyback core. In either case, failure requires replacement
of the entire unit.
 
For external multipliers, the terminals are typically marked:
 
 IN - from flyback (6-10 KV AC).
 OUT - HV to CRT (20-30 KV DC).
 F - focus to CRT (2-8 KV).
 CTL - focus pot (many megohm to ground).
 G, GND, or COM - ground.
Symptoms of tripler failure are: lack of high voltage or insufficient high
voltage, arcing at focus protection spark gap, incorrect focus voltage, other
arcing, overload of HOT and/or flyback, or focus adjustment affecting
brightness (screen) setting or vice-versa.
 
10.3) High voltage shutdown due to X-ray protection circuits
 
A TV that runs for a while or starts to come on but then shuts down may
have a problem with the X-ray protection circuitry correctly or incorrectly
determining that the high voltage (HV) is too great (risking excessive
X-ray emission) and shutting everything down.
 
A side effect of activation of this circuitry is that resetting may require
pulling the plug or turning off the real (hard) power switch.
 
Is there anything else unusual about the picture lately that would indicate
an actual problem with the HV? If this is the case, then there may be
some problem with the HV regulation. If not, the shutdown circuit may
be overly sensitive or one of its components may be defective - a bad
connection of leaky cap (or zener).
 
One symptom of excessive HV (but not required) is an overly bright picture
of reduced size.
 
The HV shutdown circuit usually monitors a winding off of the flyback
for voltage exceeding some reference and then sets a flip flop shutting
the horizontal drive off.
 
On some Sony models, a HV resistive divider performs this function and these
do fail - quite often. The red block called a 'HV capacitor' is a common
cause of immediate or delayed shutdown on certain Sony monitors and TVs.
 
10.4) Low or no high voltage
 
Most of these problems are due to faults in the horizontal deflection
system - shorted HOT, shorted windings or HV rectifiers in the flyback,
defective tripler, or other bad parts on the primary side of the flyback.
 
However, if you discover an inch layer of filth inside the TV, the HV
could simply be shorting out - clean it first.
 
In most cases, these sorts of faults will put an excessive load on the
horizontal output circuits so there may be excessive heating of the HOT
or other components. You may hear an audible arcing or sizzling sound from
internal shorts in the flyback or tripler. Either of these may bet hot,
crack, bulge, or exhibit visible damage if left on with the fault present.
 
Most modern TVs do not regulate HV directly but rather set it via
control of the low voltage power supply to the HOT (B+), by snubber
capacitors across the HOT, and the turns ratio of the flyback. The
HV is directly related to the B+ so if this is low, the HV will be low
as well. Faulty snubber capacitors will generally do the opposite - increase
the HV and the X-ray protection circuits may kick in. However, low HV
is also a possibility. The only way the turns ratio of the flyback can
change is from a short which will manifest its presence in other ways as
well - excessive heating and load on the horizontal output circuits.
 
While a shorted second anode connection to the CRT is theoretically
possible, this is quite unlikely (except, as noted, due to dirt).
 
10.5) Excessive high voltage
 
Any significant increase in HV should cause the X-ray protection circuits
to kick in and either shut down the set or modify the deflection in such
a way as to render it harmless.
 
Symptoms include arcing/sparking of HV, smaller than normal picture, and
under certain scenarios, possible excessive brightness.
 
Causes of the HV being too high are:
 
 Excess B+ voltage to the HOT. The likely cause is to a low voltage
   regulator failure.
 
 Open snubber capacitors across the HOT. These are under a lot of
   stress and are located near hot components so failure is possible.
 
 Incorrect excessively long scan drive to HOT caused by failure of
   horizontal oscillator/sync circuits. However, other things like the
   HOT will probably blow up first. The picture will definitely be
   messed up.
 
 Failure of HV regulator (tube sets and a few solid state sets - actual
   HV regulators are relatively uncommon today.) This may result in an
   underscanned (smaller than normal) picture.
10.6) Arcing, sparking, or corona from CRT HV anode (red wire/suction cup)
Symptoms could include a sizzling corona or more likely, an occasional
or rapid series of sharp snaps - possibly quite loud and quite visible - from
the anode cap on the CRT to the grounded coating on the outside of the CRT or
a chassis ground point (or any other conductor nearby). Corona is a high
resistance leakage through the air without total breakdown. The snapping
is caused by the sudden and nearly complete discharge of the CRT anode
capacitance through a low resistance ionized path similar to lightening.
There are two likely causes:
 Dirt, dust, grime, around and under the suction cup on the CRT are
   providing a discharge path. This may be more severe in humid weather.
   Safely discharge the HV and then remove and thoroughly clean the HV
   suction cup and the area under it and on the CRT for several inches
   around the HV connection. Make sure there are no loose wires or other
   possible places for the HV to discharge to in the vicinity.
 
 The high voltage has gone through the roof. Usually, the X-ray protection
   circuitry should kick in but it can fail. If cleaning does not help,
   this is a likely possibility. See the sections:
High voltage shutdown due to X-ray protection circuits
and
Excessive high voltage.
10.7) Arcing at CRT sparkgaps
 
This is rarely due to a defective sparkgap but rather is a safety mechanism
like a fuse designed to protect the internal electrodes of the CRT if the
focus or screen voltage should become excessive. The sparkgap breaks down
first and prevents internal arcing in the CRT.
 
An arcing sparkgap is usually accompanied by total loss of picture or bad
focus, brightness or focus fluctuations, or any of a number of similar
symptoms. The usual cause is a breakdown inside the focus divider inside
the flyback or tripler. Sometimes, it is in a component that can be
disassembled and cleaned but not generally. Replacement of the bad part
will be needed.
 
10.8) Arcing from flyback or vicinity
 
If the arc is coming from a specific point on the flyback - a crack or
pinhole - this may be patched using high voltage sealer or even a few
layers of plastic electrical tape. This may prove to be a permanent
repair although starting the search for a source for a new flyback
would not hurt just in case. The arc most likely did damage the insulation
internally which may or may not be a problem in the future.
 
In some cases, the pinhole or crack is an indication of a more serious
problem - overheating due to shorted windings in the flyback or excessive
secondary load.
 
First, clean the areas around the arc thoroughly and then try several
layers of plastic electrical tape. If the TV works normally for say,
an hour, then there is probably nothing else wrong and you can try for
a proper sealing job or hope that tape holds out (put a few more layers
on - each is good for about 8-10 KV theoretically).
 
If the arc is from one of the sparkgaps around the CRT, this could also
be a flyback problem indicating internal shorts in the focus/screen network.
 
Once I had a TV where the main problem was a cracked flyback arcing
but this took out one of the fusable resistors for the power supply to
the VERTICAL output so the symptoms included a single horizontal line.
Don't ask me to explain - replacing that resistor and the flyback (the
flyback tested good, but this was for someone else) fixed the TV.
 
In another case, a pinhole developed in the flyback casing probably
due to poor plastic molding at the time of manufacture. This resulted in
a most spectacular case of sparking to a nearby bracket. A few layers of
electrical tape was all that was needed to affect a permanent repair.
 
10.9) Ozone smell and/or smoke from TV
 
Smoking is just as bad for TVs as for people and usually more quickly
terminal.
 
White acrid smoke may indicate a failed electrolytic capacitor in the
power supply probably in conjunction with a shorted rectifier. Needless to
say, pull the plug at once.
 
A visual inspection should be able to easily confirm the bad capacitor as it
will probably be bulging and have condensed residue nearby. Check the
rectifier diodes or bridge rectifier with an ohmmeter. Resistance across
any pair of leads should be more than a few ohms in at least one direction.
Remove from the circuit to confirm. Both the faulty diode(s) and capacitor
should be replaced (though the capacitor may work well enough to test
with new diode(s).
 
If a visual inspection fails to identify the smoking part, you can probably
plug the set in for a few seconds until the source of the smoke is obvious
but be prepared to pull the plug in a real hurry.
 
If the smell/smoke is coming from the flyback, then it has probably gone
belly up. You may be able to see a crack or bulge in the case. While
the flyback will definitely need to be replaced, it is likely that nothing
else is wrong. However, it might be prudent to use a Variac when performing
initial testing with the replacement just in case there is a secondary
short circuit or excess HV problem.
 
10.10) Should I be worried about X-ray exposure while servicing a TV or monitor?
 
The only source of X-rays in a modern TV or monitor is from the CRT.
X-rays are generated when a high velocity electron bean strikes a
heavy metal target. For anything you are likely to encounter, this can
only happen in a vacuum - thus inside the CRT. The higher the voltage,
the greater the velocity and potential danger.
 
The thick front CRT faceplate protects users adequately but there may be some
emission from the thinner sides. At 25-30 KV (quite low as X-ray energies go)
X-rays will be stopped by almost any metal so what you have to worry about
is where there are no shields.
 
However, realistically, there is very little and I would not worry about
exposure unless you plan to be sitting for hours on the sides, behind, or
under the TV or monitor - with a picture (there will be none if the screen is
black).
 
10.11) Flyback shot by 4 year old
 
Your 4 year old son shot the Sony in the flyback transformer. Smoke and sparks
everywhere. Great aim!
 
Who says these FAQs cannot be funny?
 
Needless to say, unplug the set immediately. Inspect around the target
area for obviously blown or damaged components. Test fuses and fusable
resistors. Repair burnt solder connections and circuit board traces.
Once the set is entirely dried out, power it up - preferably through a
series light bulb and/or Variac until you are sure nothing else will
let loose. Look, listen, and smell for any unusual behavior. If it
now works, then consider yourself lucky. If not, there may be damage
to transistors, ICs, or other components.
 
(The following from: edison@nelson.planet.org.nz (Richard Symonds)).
 
We're seeing another 'hazard' these days, people cleaning their
television screens with window cleaner - no problem in the days of
separate chassis but with the entire p.c.b. jammed under the tube on
most t.v.s these days just a few drips and its all over. Some have
just corroded the switch banks (had one recently just got into the
A/V switch - when you walked around the room the set changed to A/V
and back by itself!) but a few have got around the microprocessors and
surface mount components and resulted in complete write-offs. I
suppose the damage is the opposite of electroplating as the microp's
have constant voltage to them. Never mind, they'll be a good source
of parts for future use.
Chapter 11) Raster, Color, and Video Problems
 
11.1) No color - black and white picture
 
This means absolutely no color - equivalent to a black and white picture.
Not even a hint of color.
 
First, confirm that the source is actually in color - try another channel
or input device.
 
Next, check the settings of the color control - it may have accidentally
been turned down. If your TV has some kind of automatic picture mode,
try turning if off and adjusting the color control. Try adjusting fine
tuning if you have such a control and the problem is with a broadcast
or cable transmission.
 
At this point with a confirmed color signal source, there is a problem
with the chroma circuitry.
 
Note that to the average person, the obvious question becomes: is my color
picture tube bad? The answer is a definitive NO. It is virtually impossible
for a defective CRT to cause a total loss of color. A defective CRT can
cause a lack of a primary color - R, G, or, B which will mess up the color
but is not likely to result in a black and white picture.
 
Some possibilities in no particular order:
 
 Weak signal or defect in tuner/IF causing loss of signal strength.
 Coler killer set too high (internal control) if it has one.
 Defective part around the chroma chip/circuit. Faulty color
   oscillator.
 Bad connections in area of chroma chip/circuit.
 Defective chroma chip (don't suspect this first just because it
   is probably very expensive).
A service manual or SAMs, DMM, & scope will help greatly in attempting to
troubleshoot this unless it is an obvious bad connection. Try prodding
the main board around the chroma chip with an insulated tool to see if
you can make the color come and go.
 
I had one set where a $.02 resistor decided to open up causing just this
problem - perfect BW picture, no color. Another had a coil with a broken wire.
 
11.2) Psychodelic color
 
The means colors that are not normal and that adjustment of the user
controls is not able to correct it so that all colors of the picture
are properly displayed at the same time. For example, you are unable
to get any yellows or blues in scenes that should have these colors..
 
Make sure the user color and tint controls have not been accidentally
turned while cleaning or purposedly misadjusted by small (or large) kids.
 
Perform the user setup described in the section:
User picture adjustment.
 
Confirm that the source is not a weird color video - try another
channel or a tape.
 
Verify that this is not a missing color problem - one of the primary R, G,
or B, has disappeared. If so, refer to the section:
Missing colors.
 
Once these have been eliminated, you are left with the
following possibilities:
 
 Defective part around the chroma chip/circuit. Misadjusted
   color oscillator.
 Bad connections in area of chroma chip/circuit.
 Defective chroma chip (don't suspect this first just because it
   is probably very expensive).
A service manual or SAMs, DMM, & scope will help greatly in attempting to
troubleshoot this unless it is an obvious bad connection. Try prodding
the main board around the chroma chip with an insulated tool to see if
you can restore normal color.
 
Something as simple as a bad resistor or inductor can be the cause - don't
immediately suspect the most expensive part.
 
11.3) TV and Monitor Manufacturing Quality and Cold Solder Joints
 
Any intermittent problems with monitors that cause random sudden changes in
the picture brightness, color, size, or position are often a result of
bad connections.
 
Bad solder joints are very common in TVs and monitors due both to poor quality
manufacturing as well as to deterioration of the solder bond after numerous
thermal cycles and components running at high temperature. Without knowing
anything about the circuitry, it is usually possible to cure these problems
by locating all bad solder connections and cleaning and reseating internal
connectors. The term 'cold solder joint' strictly refers to a solder
connection that was either not heated enough during manufacturing, was
cooled too quickly, or where part pins were moved before the solder had
a chance to solidify. A similar situation can develop over time with
thermal cycling where parts are not properly fastened and are essentially
being held in by the solder alone. Both situations are most common with
the pins of large components like transformers, power transistors and
power resistors, and large connectors. The pins of the components have
a large thermal mass and may not get hot enough during manufacturing. Also,
they are relatively massive and may flex the connection due to vibration
or thermal expansion and contraction.
 
To locate cold solder joints, use a strong light and magnifier and examine
the pins of large components for hairline cracks in the solder around the
pin. Gently wiggle the component if possible (with the power off). Any
detectable movement at the joint indicates a problem. With the power on,
gently prod the circuit board and suspect components with an insulated
tool to see if the problem can be effected.
 
When in doubt, resolder any suspicious connections. Some monitors may
use double sided circuit boards which do not have plated through holes.
In these cases, solder both top and bottom to be sure that the connections
are solid. Use a large enough soldering iron to assure that your solder
connection is solid. Put a bit of new solder with flux on every connection
you touch up even if there was plenty of solder there before.
 
11.4) Intermittent or Missing Colors
 
If gently whacking the set can make the color(s) come and go, then
bad connections are a very likely possibility.
 
The the effect is sudden - the color drops in and out instantly, it is
not a CRT problem.
 
If the color fades in and out with a delay of about 10-15 seconds, it is
probably intermittent power to the CRT filament for that color and probably
means a bad CRT since the three filaments are wired in parallel inside
the CRT and one of the internal connections has come loose.
 
 Look in the neck of the CRT to make sure all three filaments are
   glowing orange. If one is out or goes on and off toss the set.
   Replacing the CRT is probably not worth it. However, if they all
   go on and off together (all colors would be fading in and out though
   perhaps not quite in unison), then bad connections on the video driver
   board (on the neck of the CRT) are indicated.
 
 Locate the output for the bad color on the video driver board on the
   neck of the CRT. This will probably read a significantly higher
   voltage than the corresponding pins for the good colors. A circuit
   problem is likely - probably on this board.
 
 Test components on this board for the good and bad color channels. A
   shorted transistor or open resistor can kill one channel. Swap
   parts to confirm.
This is a catch-all for some of the most common TV and monitor problems.
 
Most of the causes of intermittent colors boil down to bad connections
of one form or another. For totally dead colors - not intermittent - bad
components are also a possibility.
 
 Printed circuit board on the CRT neck. This is a common location for
   cold solder joints. Check with a bright light and magnifying glass
   for hairline cracks around the pins of larger parts. Prod and tap with
   an insulated tool to see if the problem is effected. Resolder if necessary.
 
 Cold solder joints elsewhere in TV or monitor usually around the pins of
   large parts such as transformers, power transistors and resistors, and
   internal connectors.
 
 Internal connectors that need to be cleaned and reseated. Remove,
   clean with contact cleaner, burnish, and replace.
11.5) Red, green, or blue full on - fog over picture
 
This could be a heater-cathode (H-K) short in the CRT or a failure
of a component in the chroma circuits or video output (driver board).
 
Don't panic - heater-cathode shorts in CRTs can often be worked around.
 
Some simple tests can confirm or rule out other possibilities.
 
Compare the voltages for the video drive signals to the CRT on the little
board on the neck of the CRT with the CRT both connected and unplugged.
A schematic will help greatly in locating these signals.
 
If there is a significant difference especially on the bad color, then the
CRT is a likely candidate. Try tapping the neck of the CRT GENTLY (with
it plugged in and while viewing a picture) to see if it is an intermittent
problem. Might want to have eye protection on while doing this!
 
If there is no significant difference, you may have a bad driver or a problem
in the chroma circuits.
 
Look for bad connection/cold solder joints, probably on the little
board on the neck of the CRT. Use an insulated stick to gently prod
the board and its components in an effort to induce/cure the problem.
Look carefully for hairline cracks around the component leads.
 
You can swap components between two colors and/or test with an ohmmeter
on that driver board to determine what is bad. The nice thing about
color monitors and TVs is that there three copies of each of these
components. Swapping and/or comparisons between these is an excellent
diagnostic technique.
 
Alternatively, interchange the outputs of the bad color with a good one
by jumpering on the video driver board (on the CRT neck). If the bad
color changes, then the problem is in the circuitry and not the CRT.
 
11.6) Providing isolation for a CRT H-K short
 
This procedure will substitute a winding of your own for the one that is
built in to the flyback to isolate the shorted filament from the ground
or voltage reference. Note that if you have a schematic and can determine
where to disconnect the ground or voltage reference connection to the
filament winding, try this instead.
 
The flyback is the thing with the fat red wire coming out of it (and perhaps
a couple of others going to the CRT board or it is near this component
if your set has a separate tripler) and may have a couple of controls for
focus and screen. It should have some exposed parts with a ferrite core
about 1/2-3/4 diameter.
The filament of the CRT is the internal heater for each gun - it is what
glows orange when the set is on. What has happened is that a part of the
fine wire of the bad color's filament (assuming this is indeed your problem)
has shorted to the cathode - the part that actually emits the electrons.
Normally, the heater circuit is grounded or tied to a reference voltage
so when it shorts to the cathode, the cathode voltage level is pulled to
ground or this reference.
 
You will need some well insulated wire, fairly thick (say #18-22). Find a
spot on the flyback where you can stick this around the core. Wrap two
turns around the core and solder to the CRT filament pins after cutting the
connections to the original filament source (scribe the traces on the board
to break them). This winding should cause the filaments to glow about
the same brightness as before but now isolated from ground. If they are
too dim, put another turn on the flyback to boost the voltage. (Don't go
overboard as you may blow the filament totally if you put too many turns
on the core - you then toss the TV.) Route the wires so that there is
no chance of them getting near the high voltage or any sharp metal
edges etc. Your picture quality may be a tad lower than it was before
because of the added stray capacitance of the filament wiring being
attached to the the (formerly bad) video signal, but hey, something is
better than nothing.
 
11.7) Rescuing a shorted CRT
If the short is filament-cathode (H-K), you don't want to use the following
approach since you may blow out the filament in the process. If this is the
case, you may be able to float the filament and live with the short (see the
section on:
Red, green, or blue full on - fog over picture.
Shorts in the CRT that are between directly accessible electrodes can
be dealt with in a more direct way than for H-K shorts. At this point
you have nothing to loose. A shorted CRT is not real useful.
If the short is between two directly accessible electrodes like cathode-grid,
then as a last resort, you might try zapping it with a charged capacitor.
Start with a relatively small capacitor - say a few uF at a couple hundred
volts. Check to see if the short is blown after each zap - few may be needed.
Increase the capacitance if you fell lucky but have had little success with
the small capacitor.
 
If the fault is intermittent, you will, of course, need to catch the CRT
with the socket disconnected and the short still present. Try some gentle
tapping if necessary. If you do this with the charged capacitor across
the suspect electrode, you WILL know when the short occurs!
11.8) Brightening an old CRT
 
If performing adjustments of the internal background and/or screen controls
still results in a dark picture even after a long warmup period, the CRT
may simply be near the end of its useful life. In the old days of TVs
with short lived CRTs, the CRT brightener was a common item (sold in every
corner drugstore, it seemed!).
 
You can try a similar approach. CAUTION: this may shorten the life of
the CRT - possibly quite dramatically (like it will blow in a couple of
seconds or minutes). However, if the monitor or TV is otherwise destined
for the scrap heap, it is worth a try.
 
The approach is simple: you are going to increase the voltage to the
filaments of the electron guns making them run hotter. Hopefully, just
hotter enough to increase the brightness without blowing them out.
 
Voltage for the CRT filament is usually obtained from a couple of turns
on the flyback transformer. It is usually easy to add an extra turn or two
which will increase the voltage and thus the current making the filaments
run hotter. This will also shorten the CRT life - perhaps rather drastically.
However, if the monitor was headed for the dumpster anyhow, you have nothing
to lose.
 
There are also commercial CRT rejuvenators that supposedly zap the
cathodes of the electron guns. A TV repair shop may be able to
provide this service, though it is, at best, a short term fix.
 
11.9) Bleeding highlights
 
On very bright areas of the picture, one or more colors may bleed to
the right resulting in a trail of those colors. The difference between
this problem and the section:
Trailing lines in one or more colors
is that in this case, only highlights are affected.
 
One cause of this is that the color gain, contrast, or intensity controls
(whatever they are called on your set) are set too high. See the section
on:
Color balance.
Check the settings of any brightness limiter controls as well.
 
11.10) Trailing lines on one or more colors
 
The following is from: (Ian White (100743.1026@COMPUSERVE.COM)).
 
Check the power supplies to the video circuits as well as the CRT filament
(low heater volts can cause trailing). Also swap the the drives between the
red and green guns (or whichever color is affected in your case) or the
color output transistors. If the same color is always trailing then you
can be certain it is the tube and it will need reactivating or see the
dumpster.
 
11.11) Picture fades in and out
 
If the picture faded away on the order of 10-20 seconds (and if it comes
back, also comes up to full brightness in same time frame - possibly
with the persuasion of some careful whacking) AND with NO other
significant changes such as size, focus, etc., then take a look in the back of
the tube for the filament to be lit - the orange glow near the CRT socket. If
there is none, then you probably have a bad solder connection on the circuit
board on the neck of the CRT. Look for fine cracks around pins on that board.
Try prodding it with an insulating stick to see if the picture comes back.
Resolder if necessary. It is probably not a bad CRT as the filaments
are usually wired in parallel and all would not go bad at the same time.
 
However, if only a single color fades in and out, then a bad connection
inside the CRT is a distinct possibility - look for only one of the
filament's glow to be coming and going. This is probably not worth fixing.
 
If the picture faded away with other symptoms, then there is probably
a fault in the video amplifier/output one of its power supplies -
still probably a loose connection if you are able to get it back by
whacking.
 
11.12) Occasional brightness flashes
 
These may last only a fraction of a scan line or much much longer.
 
This could mean an intermittent fault in a variety of places including
the video circuitry and SCREEN power supply:
 
Brightness circuitry - SCREEN, master background or its power supply.
  Could be in or around flyback or focus/screen divider. Could perhaps
  be in the CRT, but probably less likely.
 
Video amp before or at chroma demodulator - since after this point, you would
  most likely get colored flashes since only one of the RGB signals would
  likely be effected.
 
If you get it from all sources, then tuner/IF is ruled out.
 
Suppose you just have no signal to a direct video input. What do you
get? If you still get flashes, it should be real easy to monitor either
the video outputs or SCREEN supply (with a HV divider on your scope) for
noise. Then trace back to power or noise source.
 
11.13) Excessive brightness and/or washed out picture
 
Excessive brightness/washed out picture is often an indication of a
problem with the SCREEN supply to the CRT. May be a bad capacitor
or resistor divider often in the flyback transformer assembly or on
the board on the neck of the CRT.
 
If the excessive brightness just developed over time, then a simple
adjustment of the SCREEN or background brightness controls may keep
it (and you) happy for a long time.
 
When good, a typical value would be in the 200-600 VDC at the CRT.
The SCREEN (may be called master brightness or background) control
should vary this.
 
It could also be a problem with biasing of the video output transistors.
There may individual controls for background brightness on the little
board on the neck of the CRT.
 
However, we are looking for a common problem since all colors are
wrong in the same way.
 
First, check for bad connections/cold solder joints by gently prodding
with an insulating stick. Check voltages and bias levels.
 
11.14) Bad focus (fuzzy picture)
 
Focus voltage on the CRT is usually in the range of 2-8 KV DC and should
be controllable over a fairly wide range by the focus pot.
 
The focus pot is usually located on the flyback transformer or on an
auxiliary PCB nearby. The focus wire usually comes from the flyback or
if the general area or from a terminal on a voltage multiplier module
in some cases. It is usually a wire by itself going to the little board
on the neck of the CRT.
 
If a spark gap (a little 2 terminal device with a 1/8 gap in the middle)
is arcing with power on, then the resistive divider has shorted inside
the flyback, focus board, or HV multiplier - whatever you TV has - and
the this unit will need to be replaced. Ditto if the SCREEN control affects
focus and/or vice-versa.
 
Using a suitable voltmeter (range at least 10KVDC), you should be able
to measure it connected and disconnected. The ground return will be the
outside coating of the CRT which may or may not be the same as the
metal chassis parts. If the voltage is very low (less than 2K) and
the pot has little effect:
 
When measured right off of the source disconnected from the CRT circuit, then
the problem is probably in the focus network in the flyback (or wherever
it originates). Sometimes these can be disassembled and cleaned or
repaired but usually requires replacement of the entire flyback or
voltage multiplier.
 
When measured with the CRT connected but reasonable with it disconnected, then
check for a bad capacitor on the little circuit board. The CRT could
also cause this but it is unlikely.
 
11.15) Focus drift with warmup or age
 
Focus is controlled by a voltage of 2-8 KV DC usually derived from the flyback
transformer and includes some resistors and capacitors. One of these could
be changing value as it warms up. (assuming nothing else changes significantly
as the unit warms up. E.g., the brightness does not decrease.)
 
Focus is usually a separate wire running from the flyback or its neighborhood
to the PCB on the neck of the CRT. Look for components in this general area.
Use 'cold spray' to isolate the one that is drifting. If you have access
to a high voltage meter, you should be able to see the voltage change as
the TV or monitor warms up - and when you cool the faulty part. If it is in
the flyback, then sometimes the part with the adjustments clips off and
can be repaired or cleaned. Most often, you will need to replace the flyback
as a unit.
 
Focus voltage is derived from a subset of te high voltage winding on the
flyback using a resistive voltage divider which includes the focus pot.
These are extremely high value resistors - 200 M ohm is common - and so
leakage of any kind can reduce or increase the focus voltage. All other
things being ok - i.e., the picture is otherwise fine - I would suspect this
type of failure rather than the CRT.
 
If you have a high voltage meter, you can measure the focus voltage to
determine if it is being changed by the focus pot and if it is in the
ballpark (2-8 KV typical). Sometimes, the part of the flyback with the
focus pot can be snapped off and cleaned or parts replaced but usually you
need to replace the whole unit. There may a capacitor or two on the PCB on
the neck of the CRT that could have increased leakage as well thus reducing
the focus voltage.
 
11.16) Bad focus and adjustment changes brightness
 
This is the classic symptom of a short between the focus and screen
supplies - probably in focus/screen divider which is part of the flyback
or tripler. If you have a high voltage meter, measuring the focus voltage
will show that (1) it is low and (2) it is affected by the SCREEN control
Similarly, the SCREEN voltage will be affected by the FOCUS control (which
is what is changing the brightness.
 
There is a slight possibility that this may be in the CRT as well. Measure
the FOCUS and SCREEN voltage with a high voltage meter. If they are identical
pull the plug on the CRT. If they are now their normal values, then a
shorted CRT is a distinct possibility - see the section:
Rescuing a shorted CRT.
 
11.17) Blank picture, good channel tuning and sound
 
Since the tuner and sound are ok, horizontal deflection which usually
generates power for most of the set is also working.
 
Does 'blank picture' means a totally black screen with the brightness and
contrast controls having no effect whatsoever? Or, is there is no picture
but there is a raster - light on the screen? The direction in which
troubleshooting should proceed differ significantly depending the answer.
 
Here are some questions:
 
 As above, is there any light on the screen at any settings of the brightness
   and contrast controls, and/or when switching channels. Can you see any
   raster scanning lines?
 
 Can you hear the high pitched (15735 Hz) of the horizontal deflection?
 
 Looking in the back of the set, can you see the glow of the CRT filament?
 
 Do you get that static on the front of the tube that would indicate that
   there is high voltage? Any cracking or other normal or abnormal sounds
   or smells?
Possible causes of no raster: no/low HV, drive to CRT bad/shut off as a result
of fault elsewhere, blanking as a result of tuner/controller malfunction,
filament to CRT not getting powered.
 
Possible causes of no video: problem in video IF, video amplifiers, video
output, cutoff due to other fault.
 
It could be as simple as a bad connection - try gently prodding the boards
with an insulated stick while watching the screen. Check for loose connectors
and reseat all internal connectors.
 
11.18) Purple blob - or worse
 
Have you tried demagnetizing it? Try powering it off for a half hour, then
on. Repeat a couple of times. This should activate the internal degausser.
See the section:
Degaussing (demagnetizing) the CRT.
 
Is there any chance that someone waved a magnet hear the tube? Remove it
and/or move any items like monster speakers away from the set.
 
Was your kid experimenting with nuclear explosives - an EMP would magnetize
the CRT. Nearby lightening strikes may have a similar effect.
 
If demagnetizing does not help, then it is possible that something shifted
on the CRT - there are a variety of little magnets that are stuck on at the
time of manufacture to adjust purity. There are also service adjustments
but it is unlikely (though not impossible) that these would have shifted
suddenly. This may be a task for a service shop but you can try your
hand at it if you get the SAMs Photofact or service manual - don't attempt
purity adjustments without one.
 
If the set was dropped, then it is even possible that the internal
shadowmask of the CRT has become distorted and you now have a hundred
pound paper weight.
 
It is even possible that this is a 'feature' complements of the manufacturer.
If certain components like transformers and loudspeakers are of inferior
design and/or are located too close to the CRT, they could have an effect
on purity. Even if you did not notice the problem when the set was new,
it might always have been marginal and now a discoloration is visible due
to slight changes or movement of components over time.
 
11.19) Color TV only displays one color
 
I assume that now you have no other colors at all - no picture and no
raster. Let us say it is red - R.
 
It is probably not the CRT. Do you have a scope? Check for the R, G,
and B video signals at the CRT. You will probably find no signals
for the defective colors.
 
This is almost certainly a chroma circuit problem as any failure of the
CRT or a video driver would cause it to lose a single color - the other
two would be ok. Therefore, it is probably NOT the CRT or a driver on
the little board on the neck of the CRT.
 
Try turning up the SCREEN control to see if you can get a G and B raster
just to confirm that the CRT is ok.
 
Locate the video drive from the mainboard for the good and a bad color.
Interchange them and see if the problem moves. If so, then there is
a video signal problem. If not, it is on the little CRT board.
 
It could be a defective chroma IC or something else in the chroma decoder.
 
11.20) Disappearing Red (or other color)
 
Problem: I have been given an old colour TV. The reception is good, but very
often, when the contrast and brightness of the TV image is low (e.g. when
a night scene is shown), the red colour slowly disappears, leaving behind
the green and blue image and many red lines.
 
The remaining red retrace are the giveaway that this is most likely not
a CRT problem.
 
(If there were no red lines, it could be the filament for the red gun
of the CRT going on and off due to a bad connection inside the CRT -
bad news.)
 
How is a black and white picture? (Turn down the color control).
 
If B/W picture is good, then the problem is somewhere back in the chroma
decoder circuitry.
 
Check the video input to the CRT video driver board and signals on that board.
If B/W picture is also bad, then you can compare red and green signals
to determine where they are becoming different. The red lines in your
description sounds like the red video output circuit is drifting and messing
up the background level, blanking, screen, or other setting. Could be a
capacitor or other component.
 
Chapter 12) Tuner and AGC Problems
 
12.1) No reception from antenna or cable
 
Make sure your source is providing a signal and that the cable connectors
are good (center pin not broken or bent). Try another TV if possible.
 
Make sure you source select switch or mode is set correctly. Someone
may have accidentally set it to direct video or AUX input.
 
Are all bands affected? If so, the tuner or IF is faulty. If there is
a lot of snow, then it is probably toward the front (circuitry wise) of
the tuner. If it is just a black screen, then it could be in the IF or
video amplifier.
 
If only certain bands are bad - channels 2-6 for example, then certain
parts of the tuner circuitry are faulty. However, make sure the CATV
mode is set correctly as this affects reception on a band-by-band basis.
 
The problems may be due to bad solder connections of the tuner shields,
connectors, coils, and other components. Try prodding the tuner to see
if you can make the problem come and go or at least change.
 
12.2) Picture is overloaded, washed out, or noisy
 
This indicates an Automatic Gain Control (AGC) problem often caused by
a dried up capacitor. You will probably need a schematic to go much
further. This could be a problem in the tuner, IF, or video amplifiers.
 
12.3) Interference when using VCR RF connection
 
(Some of these comments also apply to use of LaserDisc players, satellite
receivers, video games, or other sources with RF modulator (Channel 3/4)
outputs).
 
This may consist of patterns or lines in the picture.
 
If this only happens on the antenna or cable, it may be a problem
with these sources or the tuner in the VCR rather than the TV.
As a test, try the connecting the TV directly to the antenna or cable.
 
If it only happens on cable, there may be a (temporary) problem with
cable transmission - contact your cable company.
 
If it happens on playback of good quality (commercial) recordings, then
it could be a compatibility problem between the VCR and TV.
 
Make sure your patch cable connections are secure and that the cables
are not damaged - in particular that the center pin is intact.
 
Try fine tuning if your TV has this capability. If this does not
help, try switching the channel 3/4 selector on the VCR to the opposite
position and try that channel, sometimes one will be better than the other
particularly if one of these or an adjacent channel is active in your area.
 
If you have RCA baseband video inputs on your TV, try this connection to
the VCR. These should work better in any case.
 
Confirm that it is not actually a problem with the VCR - try another TV
if possible.
 
If you just changed your component placement, the VCR or TV may be
picking up interference from another component. Turn off everything but
the VCR and TV and see if that identifies the culprit. Move the TV
away from the VCR so see if they are interfering with each other - the
TV may be introducing interference into the VCR.
 
Occasionally, the particular patch cable or its length may affect
reception quality - try another one.
 
If none of this helps, you VCR's RF modulator may be bad or slightly
weak. Alternatively, the tuner in the TV may be faulty. If reception
is generally noisy on all sources, AGC or RF/IF alignment may need
adjusting. However, not all tuners are created equal. Your TV may
simply be making the best of a marginal situation.
A light dimmer on the same circuit as the TV may result in similar
symptoms. If you are tuning up your motorcycle (or automobile) in the
same room, this may be spark ignition interference.
12.4) Missing or noisy channel or block of channels
 
If you are unable to receive certain channels or blocks of channels,
this is a tuner problem - could be as simple as bad connections - or
even simpler:.
 
First, check to see that the tuning mode is correct - TV, CATV, as
this is the most common cause of channels 'disappearing'.
 
TV channels are assigned frequencies ranging from 72 to almost 800 MHz
depending on broadcast or cable channel assignment. To tune over such a
wide range requires splitting it up into various bands even if these are
not actually defined. If you have a varactor tuned set, then you already
know about the Vl, Vh, and U bands which may use separate front-end
components. Even modern quartz PLL synthesized tuners need to allocate
circuitry depending on frequency range. Therefore, if a block channels is
not working, it could be due to a failure of some component related to that
frequency range. Aside from looking for bad connections, resoldering the
shields and connector pins, prodding, pressing, praying, etc. you will need
a schematic to have any chance of finding such a fault.
 
There is another slight possibility. Some TVs have a parental lockout
capability (pre V-chip) to prevent kids or other unauthorized access to
selected channels. The channel selections may have been accidentally
altered. Check your user manual for instructions on programming this
feature. Even on models without this option, the same internal circuitry
could be present but not normally accessible. A power surge or stray cosmic
ray could have put the set in a screwy mode. Unplugging power for a minute or
probably a much longer time might possibly reset such an anomaly.
 
12.5) Loss of Channel after Warmup
 
If there is a general loss of picture and sound but there is light on the
screen, then most likely the tuner or IF stage is pooping out.
 
With both no sound and no picture but a raster and static, it is most
likely a problem in the tuner, power to the tuner, or its controller
(if non-knob type).
 
If it recovers after being off for a while, then you need to try a cold
spray in the tuner/controller to identify the component that is failing.
Take appropriate safety precautions while working in there!
 
If it stays broken, then most likely some component in the tuner, its
controller, or its power supply as failed. There is a slight chance that
it could be a bad solder connection - I have seen these in the tuner modules
of RCAs on several occasions (and many other manufacturers - apparently
not a solved manufacturing problem even after 40+ years!
 
12.6) Channel tuning drifts as set warms up
 
This may be a slight drift - like someone is messing with the fine tuning
or such a substantial change in tuning frequency that the channels go by
as though you are surfing.
 
Possible causes depend on tuner type:
 
 Quartz tuner (10 button direct access digital synthesizer) - For a
   slight drift, a component is probably changing value, possibly the
   crystal in the reference oscillator. For gross changes - flipping
   through channels - it is more likely to be a digital control problem -
   the microcontroller is misdirecting the synthesizer to change frequency.
 
 Varactor tuner (buttons but not direct channel access) - If only a
   single pushbutton selection is the problem, the the varactor tuning diode
   for that button is probably changing capacitance. If all channels in
   a band (Vl, Vh, U) are having a problem, it is more likely to be a
   drifting D/A or faulty AFT (Automatic Fine Tuning) circuit or power supply.
 
 Turret or switch tuner (Knobs) - A component like a capacitor is changing
   value.
You will have to get in there with a heat gun or cold spray and track it down
the old fashioned way. At least, the problem is almost certainly localized
to the tuner box (and possibly the controller if applicable).
 
As noted, gradual slight changes in tuning are likely due to frequency
determining components drifting.
 
Uncontrolled channel surfing is probably a logic problem. For the
quartz tuner, this could still be marginal connections causing the
microprocessor to misdirect the synthesizer to change channels.
 
For the latter case, particularly, the cause may still be bad connections
resulting in loss of channel memory and/or erratic behavior.
 
12.7) Noise in picture and sound due to bright scene
 
When a bright scene comes, the screen flashes and there is a lot
of noise in the sound. When a dark scene comes, there is no
flash or noise. Changing channel does not help. The noise
persists even when the sound is muted.
 
(The following is from: Lattuca@Midwest.net (Sam Lattuca))
 
When the video detector level is adjusted too high, you will get noise in
the sound while screen contains a lot of white information (i.e. letters) but
won't when only dark scenes are present. The video level adjust is usually a
small coil normally located near the IF section. Since your set is several
years old, this wouldn't be uncommon. It can be adjusted while watching the
picture and listening to the sound.
 
Chapter 13) Audio Problems
13.1) Picture fine, no audio
 
First check that any muting control is not activated. This might be
a button on the remote or set itself. If you have a headphone jack, it
may have dirty contacts as plugging in a headphone usually mutes
the speaker.
 
If the set is mono or only one channel of a stereo set is out, then
check for bad connections to the loudspeaker. Test the loudspeaker by
disconnecting one of the wires (with the power off!) and measuring its
resistance with an ohmmeter (it should be less than 100 ohms - probably
less than 8 ohms). Or momentarily touch a 1.5 volt battery to the speaker
terminals - you should get a click or pop from the speaker.
 
Next, trace back from the speaker output terminals to the circuit board
and look for bad solder connections or a loose or dirty connector.
 
If these tests do not reveal anything, you probably need a scope (or
audio signal tracer) and schematic. Or at least the part number off of
the chip. Is the final amp a chip also or just a transistor? Have you
tested the transistor? If there is little or no buzz from the speaker,
that would indicate a problem fairly near the output. If the tuner/if were
bad, I would expect some noise/humm pickup from the low level audio stages.
Get the part number off of the chip. If it is in a socket, check the
contacts for corrosion or looseness.
 
13.2) Weak or distorted audio
 
Assuming you are not attempting to play it at ear shattering levels,
this may be due to an alignment problem in the IF/audio demodulator,
a bad audio IC or other circuitry, bad connection, or a defective speaker.
 
If your TV has an earphone or audio line out jack, try this to see if it
is clear. If so, then your problem is in the final audio amp or speaker(s).
 
If only one channel of a stereo TV is affected, it is almost certainly the
audio amp or speaker for that channel. Interchange connection to the two
speakers temporarily and see if the problem moves.
 
If the problem is at all intermittent - try gently whacking the TV - then
it is likely a bad connection - either a cold solder joint or a dirty
or tired IC socket.
 
The audio amplifiers in newer TVs are almost always ICs and replacements
are usually readily available. If the IC is in a socket, remove the IC,
clean the pins and socket contacts and reinstall it. Sometimes, the contacts
on old socket lose their springiness and do not provide solid connections.
Such a socket will need to be replaced.
 
If the set uses discrete transistors, it s also possible for one of these
to become noisy.
 
If your TV is fairly old - 10 years or so - this may be an alignment problem
requiring tweaking of a coil in the sound IF. See your service manual.
It may be possible to have similar problems with newer TVs but this is
relatively rare.
 
13.3) Buzzing TV
 
Do you actually mean buzz - low frequency as in 60 Hz? Or, do you
really mean high pitched whine. If the latter, see the section:
High pitched whine or squeal from inside TV.
 
Is the buzz through the speaker or from the inside of the set?
 
If it is the speaker, then it is a design issue with the audio circuitry.
However, a buzzing that only occurs when the picture has sharply defined
text or graphics, may be an overload problem at the source - some TVs
simply handle it better than others.
 
If it is from inside the set, it is in the deflection or power supply.
 
There is a slight possibility that the AC power in your house has some
harmonic content - the waveform is not sinusoidal. This might be the case
if you try to run on the same circuit as an active dimmer or something
else with thyristor control. Proximity to heavy industry could also
cause this.
 
In neither case can you infer the severity of this annoyance from specs.
It is strictly a design (e.g. cost) issue.
 
The size of the TV is not a strong indicator of the severity of the problem
but there will be some relationship as the power levels are higher for
larger sets.
 
Possibly running on a slightly different line voltage may change it but
that is not really an option. You could try a line conditioner (not
just surge suppressor) which includes filtering. I suspect it won't make
must difference.
 
If it is in the audio circuits - from the speakers or line out - then
consider using a (HiFi) VCR for the tuner with an external stereo amp
and the internal speaker disabled.
 
If it is noise from the TV, then the best you can do is audition various
TVs very carefully to find one that you are satisfied with.
 
BTW, when I got my new super duper RCA Colortrak in 1980, it had a similar
annoying buzz - even had a repair guy out who behaved as though this was to
be expected. I did get used to it and am not even aware of it today - and
still use that set.
 
13.4) High pitched whine or squeal from TV with no other symptoms
 
First, make sure it is not coming from the loudspeaker itself. If it is,
then we are looking at an unusual electronic interference problem rather
than simply mechanical vibration.
 
There are several parts inside the TV that can potentially make this noise -
the horizontal flyback transformer and to a lesser extent, the deflection
yoke would be my first candidates. In addition, transformers or chokes
in the switching power supply if this is distinct from the horizontal
deflection circuitry.
 
I don't know about returning a set to a store that doesn't take refunds (I
won't even ask about that!) but assuming that this sound level is normal
for the particular model here are a couple of suggestions:
 
You do not want to coat the TV as this may interfere with proper cooling,
but the interior of the entertainment center cabinet could be lined with
a non-flammable sounds absorbing material, perhaps acoustic ceiling tiles.
Hopefully, not a lot of sound energy is coming from the front of the set.
 
Move the TV out of a corner if that is where it is located - the corner
will focus sound energy into the room.
 
Anything soft like carpeting, drapes, etc. will do a good job of
absorbing sound energy in this band.
 
If you are desperate and want to check the inside of the set:
 
It is possible to coat the flyback transformer, but this is used mostly
when there a loose core or windings and you are getting not only the
15,735 Hz horizontal (NTSC) but also various subharmonics of this. This is
probably acceptable but may increase the temperature of the flyback.
 
Using appropriate safety precautions, you can try prodding the various
suspect parts (flyback, deflection yoke, other transformers) with an
insulated tool such as a dry wooden stick. Listen through a cardboard
tube to try to localizing the source. If the sounds changes, you
know what part to go after. Sometimes a replacement flyback will
cure the problem unless it is a design flaw. You do not want to replace
the yoke as convergence and other adjustments would need to be performed.
Other transformers can be replaced.
 
Note that the deflection frequency - just over 15 KHz for NTSC and PAL - is
on the border of audible for adults but will likely be loud to younger people
possibly to the point of being terribly annoying - or worse. If you are
over 40 (men more so than women), you may not be able to hear the fundamental
at all (at least you can look forward to silence in the future!). So, even
sending the TV back for repair may be hopeless if the technician cannot
hear what you are complaining about!
 
Chapter 14) Miscellaneous Problems
14.1) General erratic behavior
 
You press VOLUME UP and the channel changes or a setup menu appears all by
itself just at the climax of your mystery story.
 
Before you break out the screwdriver (or 12 pound hammer), cover up the
IR remote sensor. Some types of electronic ballasted fluorescent lights
may confuse the remote control receiver. Or, someone or something may be
sitting on the remote hand unit or it may be defective and continuously
issuing a bad command!
 
Assuming this is not the source of the problem:
 
Check for bad connections - see if gently whacking the TV makes any
difference or triggers the errant behavior. Bad connections in the power
supply, system controller, or tuner, may result in this sort of behavior.
See the section:
TV and monitor manufacturing quality and cold solder joints.
 
There could also be noisy power, a defective bad microcontroller, or EEPROM.
 
14.2) Jittering or flickering due to problems with AC power
If you have eliminated other possibilities such as electromagnetic
interference from nearby equipment or a faulty video cable or problems
with the video input (e.g., cable or VCR) - then noisy or fluctuating AC
power may be a possibility. However, most modern TVs usually have well
regulated power supplies so this is less common than it used to be. Then
again, your TV may just be overly sensitive. It is also possible that
some fault in its power supply regulator has resulted in it becoming more
sensitive to small power fluctuations that are unavoidable.
One way to determine if the problem is likely to be related to AC power
is to run the TV on clean power in the same location connected to the
same video input. For example, running it on an Uninterruptible Power Source
(UPS) with the line cord pulled from the wall socket would be an excellent
test. The output of the UPS's invertor should be free of any power line
noise. If the TV's image has now settled down:
Large appliances like air conditioners, refrigerator, or washing machines
   on the same circuit might cause significant power dips and spikes as they
   cycle.
   Plugging a table lamp into the same outlet may permit you to see any obvious
   fluctuations in power. What else is on the same circuit? Depending on
   how your house or apartment is wired, the same feed from the service panel
   may be supplying power to widely separated areas.
For some unfathomable reason, your TV may just be more sensitive to
   something about the power from the circuit in that room. There may be
   nothing actually wrong, just different. While unlikely, a light dimmer
   on the same circuit could be producing line-conducted interference.
   If you have a multimeter, you could at least compare the voltages
   between the location where it has problems and the one where it is
   happy. Perhaps, the TV is sensitive to being on a slightly
   different voltage. This might only be a problem if some circuitry
   in the the TV is marginal in some respect to begin with, however.
There could be a bad connection somewhere on the circuit. If your house
   has aluminum wiring, this is a definite possibility.
   Try a table lamp since its brightness should fluctuate as well. This
   should be checked out by a competent electrician as it represents a real
   fire hazard.
An electrician may be able to pinpoint the cause but many do not have
the training or experience to deal with problems of this sort. Certainly,
if you find any power line fluctuations not accounted for by major
appliances, on the same circuit this should be checked by an electrician.
14.3) My TV has the shakes
You turn on your TV and 5-10 seconds later, the display is shaking or
vibrating for a second or so. It used to only occur when first turned on,
but now, the problem occurs 3 times in 30 seconds. Of course, many
variations on this general theme are possible.
Some possibilities:
External interference - did you change anything or move your A/V setup
   recently? Do you have a computer monitor nearby?
Defective circuitry in TV - power supply regulation, deflection,
   or bad internal connections are possible.
Defective video cable (unlikely) - wiggle the cables to be see if
   you can induce the problem.
Note that many of the soures of electromagnetic interference that are
problems with computer monitors like transformers and power lines will
not cause noticeable shaking, wiggling, or jiggling on a TV because the
power line and vertical scan are at almost exactly the same frequency
and any such movement would be very slow.
14.4) TV was rained on
 
Was the set plugged in when the leak started? Any piece of equipment with
remote power-on capability has some portions live at all times when plugged
in and so there may have been damage due to short circuits etc. Substantial
damage could be done due to short circuits.
 
Otherwise, you may just need to give it more time to dry out. I have
had devices with keypads getting wet that required more than a week but
then were fine. There are all kinds of places for water to be trapped and
take a long time to evaporate.
 
If the set got wet while unplugged (in a leaky attic or wet basement), for
example, or it has a pull or click knob on/off switch, then give it time
to dry out - completely. Assuming all visible water is drained, a week
represents a minimum safe time to wait. Don't rush it.
 
Generally, some moisture will not do any permanent damage unless the
set was on in which case you will simply have to troubleshoot it the
old-fashioned way - one problem at a time.
 
14.5) TV was dropped
 
You have probably seen the TV advertisements - I don't recall what they
were for - where a late model TV is dropped out a many story window
on a bunjie cord to rebound once undamaged and without hitting a baby in
a stroller but then smash to smithereens on the sidewalk once the stroller
had moved. Needless to say, this is generally not a recommended way to
treat a TV set!
 
However, mishaps do happen.
 
Assuming it survived mostly intact - the CRT didn't implode, you could
still have a variety of problems. Immediately unplug the set!
 
If you take it in for service, the estimate you get may make the national
debt look like pocket change in comparison. Attempting to repair anything
that has been dropped is a very uncertain challenge - and since time is
money for a professional, spending an unknown amount of time on a single
repair is very risky. There is no harm is getting an estimate (though
many shops charge for just agreeing that what you are holding was once
a - say - a TV, or was it a fishtank?)
 
This doesn't mean you should not tackle it yourself. There may be
nothing wrong or very minor problems that can easily be remedied. The
following are likely possibilities:
 
Cracked circuit boards. These can be repaired since TVs usually have
   fairly wide open single or two sided boards.
 
 Broken circuit components. These will need to be replaced.
 
 Broken solder connections particularly to large heavy components
   on single sided boards. Reflow the solder. If the trace is cracked
   or lifted, repair as in (1).
 
 Broken mounting brackets. These are usually made of cheap plastic
   and often don't survive very well. Be creative. Obtaining an
   exact replacement is probably not worth the trouble and expense.
 
 Components knocked out of line on the CRT envelope or neck - deflection
   yoke, purity magnets, convergence magnets and coils, geometry correction
   magnets. These will need to be reattached and/or realigned. Some CRTs use
   little magnets glued to the funnel portion of the CRT envelope. If any
   of these have come loose, it could be quite a treat to figure out where
   they went and in what orientation.
 
 Internal damage to the CRT - popped or distorted shadowmask, misaligned
   electron guns. Unfortunately, you will probably have no way of
   identifying these since you cannot see inside the CRT. They will not
   be apparent until all other faults have been remedied and the TV set
   is completely realigned. At that point, extremely severe purity or
   convergence problems that do not respond to the normal adjustment
   procedure would be one indication of internal damage. Give the TV a
   nice funeral.
If you still want to tackle a restoration:
 
As noted, unplug the TV even if it looks fine. Until you do a thorough
internal inspection, there is no telling what may have been knocked
out of whack or broken. Electrical parts may be shorting due to a broken
circuit board or one that has just popped free. Don't be tempted
to apply power even if there are no obvious signs of damage - turning
it on may blow something due to a shorting circuit board. If it is a
portable, remove the batteries.
 
Then, inspect the exterior for cracking, chipping, or dents. In addition
to identifying cosmetic problems, this will help to locate possible areas to
check for internal damage once the covers are removed.
 
Next, remove the cover. Confirm that the main filter capacitors are
fully discharged before touching anything. Check for mechanical problems
like a bent or deformed brackets, cracked plastic parts, and anything that
may have shifted position or jumped from its mountings. Inspect for loose
parts or pieces of parts - save them all as some critical magnets, for
example, are just glued to the CRT and may have popped off.
 
Carefully straighten any bent metal parts. Replace parts that were
knocked loose, glue and possibly reinforce cracked or broken plastic.
Plastics, in particular, are troublesome because most glues - even plastic
cement - do not work very well. Using a splint (medical term) or sistering
(construction term) to reinforce a broken plastic part is often a good
idea. Use multiple layers of Duco Cement or clear windshield sealer
and screws (sheetmetal or machine screws may be best depending on the
thickness and type of plastic). Wood glue and Epoxy do not work well
on plastic. Some brands of superglue, PVC pipe cement, or plastic hobby
cement may work depending on the type of plastic.
 
Inspect for any broken electronic components - these will need to be replaced.
Check for blown fuses - the initial impact may have shorted something
momentarily which then blew a fuse.
There is always a risk that the initial impact has already fried electronic
parts as a result of a momentary short or from broken circuit traces and
there will still be problems even after repairing the visible damage and/or
replacing the broken components. This is most likely if the set was actually
on but most modern TVs have some circuitry energized at all times.
Examine the circuit boards for any visible breaks or cracks. These will
be especially likely at the corners where the stress may have been greatest.
If you find ANY cracks, no matter how small in the circuit board, you
will need to carefully inspect to determine if any circuit traces run
across these cracks. If they do, then there are certainly breaks in
the circuitry which will need to be repaired. Circuit boards in consumer
equipment are almost never more than two layers so repair is possible but
if any substantial number of traces are broken, it will take time and patience.
Do not just run over them with solder as this will not last. Use a fine
tipped low wattage soldering iron and run #22-26 gauge insulated wires
between convenient endpoints - these don't need to be directly on either
side of the break. Double check each connection after soldering for correct
wiring and that there are no shorts before proceeding to the next.
If the circuit board is beyond hope or you do not feel you would be able
to repair it in finite time, replacements may be available but their cost
is likely to be more than the equipment is worth. Locating a junk unit of the
same model to cannibalize for parts may be a more realistic option.
Degauss the set as any impact may magnetize the CRT. Power cycling may
work but a manual degaussing is best.
Once all visible damage has been repaired and broken parts have been replaced,
power it up and see what happens. Be prepared to pull the plug if there
are serious problems (billowing smoke or fireworks would qualify).
Perform any purity, convergence, or other realignment as needed.
Then proceed to address any remaining problems one at a time.
14.6) Setup menus will not go away or hieroglyphics on screen
 
Both these problems could be caused by a faulty microcontroller or
its associated circuitry. However, bad connections in the vicinity
of the controller logic could also be at fault.
 
Unless you see something obvious, you will need schematics.
14.7) Setup Adjustments Lost
 
Many modern TVs have RAM, somewhat like the CMOS SETUP memory in your PC,
that store all factory adjustments. When power is lost, there is power
surge, lightening strike nearby, nuclear detonation or EMP, it may
have put bad information into the ram and thrown it out of adjustment. There
is a way to get into the service mode (depress and hold a secret button
down and turn set on, special combination of buttons on the remote, etc.)
and then use the remote to reinitialize and adjust the problems out.
 
HOWEVER, IF YOU DON'T KNOW WHAT YOU DOING YOU COULD GIVE YOURSELF WORSE
PROBLEMS. YOU COULD EVEN BLOW THINGS OUT WITH SOME SETS!
 
The SAMS Photofact manual describes this process - you may be able to get
Photofacts from a local library, or you can buy them from Radio Shack or
a place like MCM Electronics or an electronics distributor.
 
Example: Sony with vertical deflection problems after power failure:
 
The following is from (Rob myers, myer3812@nova.gmi.edu).
 
I think, at least on a KV-20EXR10, you hold down the secret button while
turning on the set. An on screen menu appears, and the numeric keys make
adjustments and select the adjustments to make. I think you use 1/3 and 4/6
or 4/6 and 7/9 to do this. The secret button is a small black recess in the
video jack/ antenna panel. The adjustments you may need to make are vertical
linearity and pincushioning. I strongly suggest you get the SAMS manual
before you start making changes.
 
If it is not an adjustment problem you probably have a bad part in the
vertical power supply or output (perhaps $150 or less to get repaired???)
Once again, try not to make any unnecessary changes and document every change
you make!!! That way you can go back if you do anything wrong (hopefully).
I think the SAMS manual also tells you how to restore factory settings.
 
14.8) TV doesn't work after being in storage
 
So the TV you carefully stuffed in a corner of the garages is now totally
dead. You swear it was working perfectly a year ago.
 
Assuming there was absolutely no action when you turned it on, this has
all the classic symptoms of a bad connection. These could be cold/cracked
solder joints at large components like transformers, power resistors, or
connectors and connectors that need to be cleaned or reseated. By 'no action'
I mean not even a tweet, bleep, or crackle from anything.
 
To narrow it down further, if careful prodding with a well insulated stick
does not induce the set to come on, check the following:
 
 Locate the horizontal output transistor. It will be in a TO3 metal
   (most likely on an older set) or TOP3 plastic package on a heat sink.
   With power off, measure collector to emitter with an ohmmeter - in at least
   one direction it should be fairly high - 1K or more. Then clip a voltmeter
   on the 250 V DC or higher scale across C-E and plug in and turn on the set.
   Make sure it is well insulated.
 
 If the problem is in the low voltage (line) power supply, there will
     be no substantial voltage across C-E.
 
     You should be able to trace from the power line forward to find the bad
     part though a schematic will help greatly.
 
 If the problem is in the startup circuit or horizontal oscillator/driver,
     then there will be something on the order of 100-160 V across C-E.
 
     In this case, a schematic may be essential.
 
NOTE: don't assume that the metal parts of the chassis are ground - they
may be floating at some line potential.
 
There is also a slight chance that there is a low voltage regulator
in addition to the horizontal output, so don't get them confused. The
horizontal output transistor will be near the flyback transformer and
yoke connector.
 
14.9) Older TVs with multiple intermittent problems
 
If the set is say, a GE, with a manufacturing date around 1980, it is possible
you have one of those circuit boards best described as bad solder joints
held together with a little copper. In this case, prodding may get the set
started. The circuit boards in these sets were double sided using what
were called 'rivlets' for vias. The rivlets were relatively massive -
literally little copper rivets - and they were not adequately
heated during assembly so there were bucketloads of cold solder joints
that showed up during middle age. I repaired one of these by literally
resoldering top and bottom of every one of the darn things with a high
wattage iron.
 
14.10) TV has burning smell
 
Assuming there are no other symptoms:
 
If this appears after extended operation - an hour or more - it may
just be a build up of dust, dirt, and grime over the years. After
understanding the safety info, some careful vacuuming inside may help.
Just don't be tempted to turn any screws or adjustments!
 
Dust is attracted to the high voltage section in particular - even the
front faceplate of the CRT collects a lot and should be wiped with a damp
cloth from time to time.
 
If the symptoms develop quickly - in a few minutes or less, then there
could still be a dust problem - a power resistor may be heating a wad of
it but other possibilities need to be considered.
 
If not dust, then probably in the power supply but realize that TVs don't
have a nice metal case labeled 'power supply'. It is just a bunch of stuff
scattered around the main board. Without identifying the part that is
heating, a diagnosis is tough especially if the set really does
work fine otherwise. However, if a series regulator were faulty and putting
out too much voltage, the set could appear to work properly but in fact
have excessive power dissipation in certain components. If cleaning the dust
does not solve the problem, you will probably need a schematic to identify
the correct voltages.
 
14.11) Revival of dead or tired remote control units
 
There are two types of problems with hand held remote controls: they
have legs of their own and they get abused or forgotten. I cannot
help you with walking remotes.
 
Where response is intermittent or the reliable operating distance is
reduced, first check the batteries and battery contacts. If some buttons
are intermittent or dead, than the most likely cause is dirty or worn
contacts under the rubber buttons or on the circuit board.
 
If there is no response to any functions by the TV or VCR, verify that any
mode switches are set correctly (on both the remote and the TV or VCR).
Unplug the TV or VCR for 30 seconds (not just power off, unplug). This
sometimes resets a microcontroller that may have been confused by a
power surge. Confirm that the remote has not accidentally been set to
an incorrect mode (VCR instead of TV, for example). If it a universal
type, it may have lost its programming - reset it. Make sure you are
using the proper remote if have multiple similar models.
 
Test the remote with an IR detector. An IR detector card can be purchased
for about $6. Alternatively, build the circuit at the end of this document.
If the remote is putting out an IR signal, then the remote or the TV or VCR may
have forgotten its settings or the problem may be in the TV or VCR and not
the hand unit. The following is just a summary - more detailed information
is available in the companion document:
Notes on the Repair of Hand Held Remote Controls.
 
Problems with remote hand units:
 
All except (1) and (2) require disassembly - there may be a screw or two and
then the case will simply 'crack' in half by gently prying with a knife or
screwdriver. Look for hidden snap interlocks.
 
  Dead batteries - solution obvious.
 
  Corroded battery contacts, Thoroughly remove chemical deposits. Clean
    contacts with pencil eraser and/or sandpaper or nailfile.
 
  Broken connections often between battery contacts and circuit board,
    possibly on the circuit board - resolder.
 
  Bad resonator or crystal - replace, but diagnosing this without
    an oscilloscope may be tough. Broken connections on resonator legs
    are common.
 
  Dirt/spills/gunk preventing keys from operating reliably. Disassemble
    and wash rubber membrane and circuit board with water and mild detergent
    and/or then alcohol - dry completely.
 
  Worn or corroded contact pads on circuit board. Clean and then use
    conductive Epoxy or paint or metal foil to restore.
 
  Worn or dirty pads on rubber keypad. Clean. If worn, use conductive
    paint or metal foil to restore.
 
  Cracked circuit board - can usually be repaired as these are usually single
    sided with big traces. Scrape off insulating coating and jumper breaks
    with fine wire and solder.
 
  Bad LED. If IR tester shows no output, remove LED and power it from
    a 9V battery in series with a 500 ohm resistor. If still no output,
    replace with readily available high power IR LED. Otherwise, check
    driver circuits.
 
 Bad IC - if it is a custom chip, forget it! Failure of the IC
    is usually quite unlikely.
 
   (The following is from Duane P Mantick:)
 
   An awful lot of IR remotes use IC's from the same or similar series. A
   common series comes from NEC and is the uPD1986C which, incidentally is
   called out in the NTE replacements book as an NTE1758. A lot of these
   chips are cheap and not too difficult to find, and are made in
   easy-to-work-with 14 or 16 pin DIP packages. Unless you have no soldering
   or desoldering skills, replacement isn't difficult.
There are a large variety of universal remotes available from $10-$100. For
general TV/VCR/cable use, the $10 variety are fine. However, the preprogrammed
variety will not provide special functions like programming of a TV or VCR.
Don't even think about going to the original manufacturer - they will charge
an arm and a leg (or more). However, places like MCM Electronics do stock a
variety of original remotes - prices range from $9 - $143 (Wow $143, for just
a stupid remote! It doesn't even have high definition sound or anything
exotic). The average price is around $40.
14.12) Loudspeakers and TVs
 
Loudspeakers incorporate powerful magnets - the larger the speaker, the
larger the magnet. However, anyone who goes ballistic when the mention
is made of a loudspeaker near a TV or monitor, should take their Vallium.
 
The fringe fields outside the speaker box will not be that great. They
may affect the picture perhaps to the point of requiring degauss. The
normal degauss activated at power-on will usually clear up any color purity
problems (assuming the loudspeakers have been moved away). At worst, manual
degauss will be needed. The CRT will not be damaged. The maximum
field - inaccessible at the voice coil - is quite strong. However, even
for non-shielded loudspeakers, the magnetic field decays rapidly with
distance especially since the core structure is designed to concentrate
as much of the field as possible in the gap where the voice coil travels.
 
However, keeping speakers away from CRTs is a good idea.
 
Now, you really should keep your superconducting magnetic resonance imager
magnet at least in the next room.....
 
14.13) Should I replace all the electrolytic capacitors if I find a bad one?
 
When a bad capacitor is found in a TV, the question of course arises
as to the likelihood of other capacitors going bad in short order.
It might be worth checking (other) caps in the power supply or hot
(temperature) areas but you could spend you whole life replacing ALL
the electrolytics in your older equipment!
 
Always confirm the customer's complaints first!! Then verify that
everything else works or you will never know if your efforts have
affected something unrelated.
 
(Original request from rogerj@apex.com):
 
A sweet little old lady has duped me into repairing her old G.E. 13 color
TV. Wanted me fix bad volume pot..... oh it has such a good picture...
she says.
Stupidly w/o even turning it on, (big mistake) I begin to open the set.
After 15-20 min. of travail, I discover that a previous repairman has glued
the case shut!
Now w/ set open, I turn it on and this picture is LOUSY. Bad color, and very
poor convergence. But I don't know if I'm to blame for banging it around
trying to open it up. Also, no horizontal or vertical hold. (fixed that
wiht a few caps). This thing has probably been sitting around for a few
years.
Well, you certainly did not kill the caps. Anything that sits for a few
years - probably in a damp unheated attic - is suspect.
 
Did you find the adjustments on the yoke assembly tight? If so, you probably
did not move anything very much either. She may remember the good picture
it produced before being stuffed away in the attic.
Anyway after going through all the adjustments, the convergence at the sides
is still bad and the horizontal size is a tad insufficient (w/no adjustment
available)
Could be that the convergence (including pincushion) circuits are still
faulty - not just misadjusted.
 
Other things that can effect horizontal size while still giving you a complete
picture:
 
 Voltage to horizontal output transistor low. Is there a voltage regulator
   in your set? The one I have has none. I assume your line voltage is ok.
 
 Increased resistance or inductance of the yoke windings. For all
   you know, the yoke may have been replaced with the wrong part.
 
 Yoke improperly positioned on tube neck.
 
 Excessive high Voltage. This is usually not adjustable.
I bet the thing hasn't worked properly in 10 years.
 
14.14) Phantom spot or blob on CRT after set is shut off
 
Why is there a splotch of colored light at the center of the CRT after
I kill power to my TV? Why does this not happen if the plug is pulled
instead? It seems to last for hours (well maybe minutes at least).
 
This problem sounds like field emission from the CRT cathode for one or
more guns. Even with the filament off, there may be some electron emission
from the cold cathode due to the strong high voltage (HV) electric fields in
the electron gun. I do not know how likely this is or why this is so.
 
When turned off with the remote or power button, you are not actually
killing AC power but are probably switching off the deflection and signal
circuits. This leaves the HV to decay over a few minutes as it is drained
by the current needed to feed the phantom spot or blob.
 
When you pull the plug, however, you are killing AC input and all the
voltages decay together and in particular, the video signal is still
present for long enough to keep the brightness up and drain the HV quickly.
 
A proper design (who knows, yours may simply have been broken from day 1)
would ensure that the HV is drained quickly or that the other bias voltages
on the CRT are clamped to values that would blank the CRT once the set is off.
If the problem developed suddenly, then this circuitry may have failed.
On the other hand, if it has been gradually getting more pronounced, then the
characteristics of the CRT or other circuitry may have changed with age.
 
It may not be worth doing anything to 'fix' this unless the splotch is
so bright (more so than normal video and for an extended time) that
CRT phosphor damage could result. On the other hand, It may provide
for some interesting conversation at your next party.
 
14.15) Disposing of dead TVs (CRTs and charged HV capacitors)
 
I don't know what the law says, but for safety, here is my recommendation:
 
Treat the CRT with respect - the implosion hazard should not be minimized.
A large CRT will have over 10 tons of air pressure attempting to crush it.
Wear eye protection whenever dealing with the CRT. Handle the CRT by the
front - not the neck or thin funnel shaped envelope. Don't just toss it
in the garbage - it is a significant hazard. The vacuum can be safely
released (let out? what does one do with a vacuum?) without spectacular
effects by breaking the glass seal in the center of the CRT socket (may be
hidden by the indexing plastic of the socket). Cover the entire CRT with
a heavy blanket when doing this for additional protection. Once the vacuum
is gone, it is just a big glass bottle though there may be some moderately
hazardous materials in the phosphor coatings and of course, the glass and
shadowmask will have many sharp edges if it is broken.
 
In addition, there could be a nice surprise awaiting anyone
disconnecting the HV wire - that CRT capacitance can hold a charge for
quite a while. Since it is being scrapped, a screwdriver under the
suction cap HV connector should suffice.
 
The main power supply filter caps should have discharged on their own
after any reasonable length of time (measured in terms of minutes, not
days or years).
 
Of course around here, TVs are just tossed intact which is fortunate
for scavengers like me who would not be happy at all with pre-safed TVs!
 
15.1) An informal history of X-ray protection
(The following is from: Marty).
 
Most of the old tube type color TV sets used a shunt HV regulator tube,
usually a 6BK4. If it failed, or some component in the HV circuit failed, the
high voltage, normally 25KV, could go up to 35KV or more, causing some X-Ray
leakage from the CRT. In the early 70s when news of this radiation scare was
first announced, there was a public outcry to immediately fix the problem. The
feds hastily imposed a requirement on manufacturers of TV sets to somehow
render a TV set unwatchable if the HV exceeded rated limits.
 
The manufacturers first response was to follow the letter of the law and the
first HEW circuit simply blanked the video when the HV exceeded a setpoint
to make the set unwatchable.
 
It was quickly noticed that the HV was not turned off with this circuit and
the CRT still could emit some radiation. Many TV sets with this feature were
left on so the consumer could listen to the sound, so the feds tightened the
requirement.
 
By this time new TV sets were all solid state and some manufacturers
experimented with HV shutdown circuits, but most of these circuits were poorly
designed and not reliable.
 
Zenith thought they had the answer by regulating the HV with a bank of 5
capacitors across the horizontal output transistor to hold down the HV to
25KV. If one capacitor opened, the HV would only rise about 2KV, not a
dangerous situation. This wasn't good enough for the feds.
 
The fix that Zenith finally came out with, was a 4 legged capacitor. Two
legs were the emitter return for the horizontal output transistor, & two legs
were the HV holddown capacitor (the equivalent value of the bank of 5 caps).
This fix was accepted by HEW and millions of TVs were produced. It worked
so well, that other manufacturers soon followed the lead (Magnavox, GE, etc.).
 
Then the worst happened! The 4 legged monsters started failing in a large
numbers. Not opening completely & not shorting out. They sometimes allowed the
HV to skyrocket to over 50KV. Some of them even cut the necks off of the CRTs.
 
Zenith issued a recall on those models with the problem (more than one entire
model year). After several improved versions of the capacitor, the
problem was fixed but that recall almost bankrupted the company. Other
companies had failures too, but usually not as dramatic as Zenith's.
 
Magnavox used the HV holddown capacitor, both single & 4 leg version in
several 70s era TV sets and is a good candidate for fireworks as well.
 
15.2) Memory chips in TVs
 
(From: Mark Zenier (mzenier@eskimo.com or mzenier@netcom.com)).
 
Actually, they are EEPROMs. A modern TV has integrated the circuitry
so that the microprocessor that controls it also sets the various
adjustments like vertical height and other characteristics. The same
memory that knows what channels are valid and what the brightness and
other user adjustable settings are is used for factory adjustments that
are set when the TV is first turned on. It's a lot cheaper to use the
remote control signals that are already there than add a handful of
trimmer resistors.
 
For service purposes there is often a magic key sequence used with your
remote control to access a service page in the on screen display than
can change these. Since you can easily set something that could fry the
various high power deflection circuits, getting a little too curious can
void your warranty, and toast your set.
 
15.3) Tony's notes on setting convergence on delta gun CRTs
 
(This section from: ard12@eng.cam.ac.uk (A.R. Duell))
 
The older delta-gun tubes (3 guns in a triangle, not in a line) can give
EXCELLENT pictures, with very good convergence, provided:
 
 You've set those 20-or-so presets correctly - a right pain as they
   interact to some extent.
 
 The CRT is set up in the final position - this type of tube is more
   sensitive to external fields than the PIL type.
Both my delta-gun sets (a B&O 3200 chassis and a Barco CDCT2/51) have
very clearly set out and labeled convergence panels, and you don't need a
service manual to do them. The instructions in the Barco manual are
something like:
Apply crosshatch, and adjust the controls on the convergence board in
the numbered order to converge the picture. The diagrams by each control
show the effect.
 
Here's a very quick guide to delta gun convergence where the settings are
done using various adjustments on the neck of the CRT (if you don't have a
service manual but do know what each control does, and where they all are -
otherwise, follow the instructions in the service manual --- sam):
 
 Apply a white crosshatch or dot pattern to the set. Don't try and
   converge on anything else - you'll go insane. It's useful to be able to
   switch between those 2 patterns.
 
 Before you start, set the height, width, linearity, pincushion, etc. They
   will interact with the convergence. Also check PSU voltages, and the EHT
   voltage if it's adjustable. That's where you do need a service manual, I
   guess.
 
 Turn off the blue gun using the A1 switch, and use the red and green
   static radial controls to get a yellow crosshatch in the middle of the
   screen. These controls may be electrical presets, or may be movable
   magnets on the radial convergence yoke (the Y-shaped think behind the
   deflection yoke).
 
 Turn on the blue gun and use the 2 blue static controls (radial and
   lateral) to align the blue and yellow crosshatches at the center of the
   screen. Some manufacturers recommend turning off the green gun when doing
   this, and aligning red with blue (using *only* the blue controls, of
   course), but I prefer to align blue with yellow, as it gives a check on
   the overall convergence of the tube.
 
 Turn off the blue gun again. Now the fun starts - dynamic convergence.
   The first adjustments align the red and green crosshatches near the edges -
   I normally do the top and bottom first. There will be 2 controls for
   this, either a top and a bottom, or a shift and a linearity. The second
   type is a PAIN to do, as it's not uncommon for it to affect the static
   convergence.
 
 Getting the red and green verticals aligned near the edges is a
   similar process.
 
 You now have (hopefully) a yellow crosshatch over the entire screen.
 
 Now to align the blue. This is a lot worse, although the principle is
   the same. Turn on the blue gun again, and check the static (center)
   convergence
 
 To align the blue lines with the yellow ones, you'll find not only
   shift controls, but also slope controls. Use the shift controls to align
   the centers of the lines and the slope controls to get the endpoints
   right. These interact to some extent. You'll need to fiddle with the
   controls for a bit to work out what they do, even if you have the manual.
 The convergence over the entire screen should now be good....
 
A word of warning here... The purity is set by ring magnets on almost all
colour CRTs, but on PIL tubes, there are other ring magnets as well -
like static convergence. Make sure you know what you are adjusting.
 
15.4) Saga and general setup for large CRT TVs
 
(Responses from: Tony (ard12@eng.cam.ac.uk), panic from V.K.)
I'm having problem(s) with a brand new 40 Mitsubishi tube (direct
view) TV. I'm writing this with hopes of getting some basic information
so that the dealer doesn't bamboozle me.
>From first viewing (5 minutes after the delivery man departed). I noticed a
discoloration patch in the top right hand corner (purple when the
background is blue/greenish when background is white).
As you probably know, a colour TV produces a red picture, a green picture
and a blue picture on the screen at the same time. You eyes interpret
that as a coloured picture. If you look at (a normal, non-projection) TV
screen through a magnifying lens, you should be able to see red, green
and blue dots, and no other colours.
 
Now, there are 3 basic adjustments to getting a good colour picture :
 
 Purity. This means that the red picture is only red, the green picture
   only green, etc. This is the one that needs setting up on your set - you
   have a purity problem
 
 Convergence. This means that the 3 pictures line up over the entire
   screen (or as much of it as possible). If this one is wrong, you'll see
   coloured fringes around objects in the picture.
 
 Grey scale. This sets the overall colour of the picture - it means
   that white is really white, etc. It varies the relative intensities of
   the red, green and blue pictures.
I called the store in a panic and they calmly told me to
press the degauss button to eliminate the problem (which I
quickly learned was spurious magnetization, caused perhaps by
storage near a speaker in the warehouse?). Result? Better but not cured.
Yes, spurious magnetization (or more correctly a different magnetic field
around the tube from the one present when it was set up) will cause
purity problems.
 
The next day I visited the store, and the manager said (again) that
this was an easily fixable problem, requiring a few waves of
a degaussing coil. To appease me, he sends the salesman home
with me with small (1 foot diameter) coil in tow. Salesman (boy,
actually) waves the coil in front of and around set and can't seem to
perfectly
Argh... Here's what should have been done IMHO.
 
 The set should have been degaussed (a fancy word for demagnetized).
 
 They should have connected a 'pattern generator' to the set. This is a
   piece of equipment that generates various test signals. They should have
   selected 'red raster' (which will appear to you as a pure red screen),
   and set up the purity adjustments on that. You should ask to see the pure
   red raster (and pure green and pure blue if the generator will allow it),
   and make sure there are no strange-coloured patches. If you like, you can
   examine the screen through a magnifying lens to check that there are no
   dots of other colours appearing - I do that when I'm setting up a new TV
   or monitor.
 
 They should then have displayed a 'cross hatch' on the screen. This is
   a grid of white vertical and horizontal lines. Convergence errors are
   shown by the lines splitting into 2 or more colours (normally one of the
   'primary colours' - red, green, or blue, and its complementary colour
   (cyan, magenta, and yellow)). Note, however, that it's VERY difficult
   or even impossible to get perfect convergence over the entire screen on a
   modern tube, and that you'll not notice small errors near the corners
   on a TV screen. Note that some engineers prefer to set up the convergence
   on some other type of display (dots, for example), but you should at
   least be able to see a cross hatch pattern (all pattern generators
   provide that one)
 
 They should have then displayed a 'grey scale' test display. This is a
   pattern of vertical grey bars of different brightnesses, from black to
   white. They should all have been a neutral grey, without colouration.
Note that convergence and purity interact to some extent, and thus if
either is adjusted, both must be checked (and rechecked). Grey scale
adjustments interact with nothing else.
 
I would want to see the set on a pattern generator (at least the patterns
I've mentioned above) and identify the problems.
To demagnetize the TV, he says that a large coil is required, that
encompasses the whole unit; service rep will 'be in touch'.
I've never heard of that - the correct procedure is to wipe the coil
around the front, top, sides and bottom NOT the back and then move it
2-3m from the set before turning it off. It doesn't matter whether the
set is on or off for this, btw. I've not heard of putting a large coil
round the entire set. (See the section:
Degaussing (demagnetizing) CRTs).
After the sales boy leaves, I could SWEAR that the picture quality
in general is decreased, with people (especially their extremities like
lips and ears) appearing pinker than before, and also more general
interference (fringes/noise) noticeable.
The convergence and purity are set by ring magnets on the neck of the
tube. It's possible that the degaussing procedure has slightly
demagnetized these, and if so, the whole set will need to be set up.
Similarly, if any part of the set was magnetized at the factory, then the
adjustments may have been set up to compensate, and then after
demagnetization, they'll need to be reset.
 
So my questions are these. Can the original problem truly be FIXED
with proper sized coil and application?
I don't think the size of the coil will make any difference. I would want to
see that set on a pattern generator, so I could be SURE as to what the
problems are. If the dealers don't have a pattern generator, then they're
not fit to be fixing TVs IMHO.
 
Could I be imagining that the waving of the small coil degraded the
picture quality?
It's possible, but fairly unlikely. See above
Should I demand replacement to a new set? Can I legally ask for
this, or is it like a new car...you own it, now you deal with
the service guys forever.
I don't know US law, but in the UK, if a product is defective, you can
demand a refund of the money paid (not a replacement or a repair, a refund).
IMHO, a TV with incorrect colours is defective...
 
15.5) About Instant On TVs
 
Most TVs built since, say, 1980 have only the microcontroller
powered from a small transformer when the set is off. This permits the
remote control or front panel pushbutton to switch the set on. This circuitry
should be no more prone to catastrophic failure than what is in a VCR or
digital clock.
 
Historically, there were 'instant on' TVs which kept a substantial portion
of their circuitry live all the time - especially those using vacuum tubes
in at least part of the circuitry (other than the CRT). In these, there
was a lot more to fail. Those tubes would continue to change their
characteristics for many minutes when warming up. Circuits were also much more
touchy - remember all that constant tweaking! Thus, it made sense from
the users's perspective to eliminate the warmup period and keep those tubes
toasty all the time.
 
In modern solid state TVs, the only component to really need a warmup period
is the CRT. All this means is that you have to wait 20 seconds for
the picture to appear.
 
15.6) Can I add an S-Video input to my TV or VCR?
 
Possibly, but why bother? You will most likely be limited by the TV or
VCR's circuitry anyhow.
 
All S-Video means is:
A special connector
Separate luminance (Y)
Chrominance (C)
rather than composite video.
 
In a VCR, you will need to bypass the input circuitry and get to the place
where Y and C are separate. This may or may not be possible depending
on its design.
 
In a TV, they may never be separate and you will need to substitute your own
circuitry for the chroma demodulator.
 
It is probably not worth it as you will likely not gain much in picture
quality but if you really are determined, a schematic will be essential
in either case.
 
If all you want to do is allow for an S-video input, there are single
chips which will combine the Y and C into a normal composite video
signal.
 
Also, see the section:
How do I add A/V inputs to a TV which does not have them built in?
since there may be safety implications in the case of adding S-Video to a
TV without any A/V jacks.
 
15.7) How do I add A/V inputs to a TV which does not have them built in?
 
The place to do this is after the video and audio IF where baseband
signals are normally separate. Depending on the model of TV, this
may be trivial to impossible - or a serious safety hazard.
 
Trivial: many low-end models use the same chassis (read this: circuit board)
as the high end A/V receivers. Either there will be some parts missing,
a cable connection to the missing A/V panel, or a missing auxiliary board
which would have the A/V interface and jacks. If this is the case with
your model, then it should be straightforward and safe to tap into the
circuits at that point.
 
If, on the other hand, everything is crammed onto a single circuit board
with no evidence of A/V signals, it may be very difficult as suitable
tap-in points may simply not be available.
 
Hazardous: many TVs have circuitry which is not isolated from the AC line.
If this is the case with your set, then it may be more trouble than it is
worth to provide the essential isolation barrier between the TV and your
external A/V equipment.
 
Unless you intend to always use the direct A/V inputs and forgo the tuner,
you will need some way of selecting between them - a switch or relay.
This could be manual - you push a button or flip a switch - or automatic.
There are all kinds of ways to doing the detection - mechanical, checking
for a low impedance connection, looking for a signal, using a switch, etc.
 
You will need a schematic - don't attempt this without one (for safety, if
no other reason).
 
15.8) Turning a TV (or monitor) into an oscilloscope?
This question comes up so often and it does sound like a neat project to
give a defunct TV a second life. Don't expect to end up with a Tek 465
on the cheap when you are done. However, it could be a fun learning
experience.
You will be severely limited in the performance of such a scope. TVs and
monitors are designed to operate at a very narrow range of horizontal scan
rates and the high voltage is usually derived from the horizontal deflection.
So, you would need to retain the original deflection system for this purpose
at least.
 You will need to disconnect the defection yoke from the horizontal and
   vertical deflection circuits of the TV or monitor without killing the HV.
   (also, doing all this without killing yourself as well). Depending on
   the design, this may be as simple as unplugging the yoke connector. More
   than likely, you will need to substitute a load for the horizontal
   deflection coil. A coil from another sacrificial similar TV or monitor
   would probably suffice.
WARNING: at this point you have a really bright spot in the middle of the
screen which will turn to a really black spot if the brightness is not turned
way down really really quickly.
 For the horizontal, you need a ramped current source. You are driving
   a non-ideal inductor (the deflection coil) so it has both inductance and
   resistance. Thus the waveform is a trapezoid - a voltage ramp (for the
   resistive part) superimposed on a voltage step (for the inductive part).
   This should not be too difficult. Don't expect to be able to achieve
   really fast sweep. Even running at normal TV rates is non-trivial.
 
 Similarly, for the vertical you need to drive with a voltage (your signal)
   controlled current source. However, if you just screwing around, then the
   linearity etc. for the vertical may not be that important. In this case,
   one way is to put a current sensing resistor in series with the deflection
   coil and use this in a power op amp type of feedback arrangement. (You
   could do this for (2) as well.
 
 There is a good chance that the original brightness control will work
   as an intensity adjustment. However, with some TVs and monitors, this
   depends on receiving a valid video signal. You may need to improvise.
   If you do want to control the intensity from a signal source, you
   should be able to tap into the drive signals going to the little board
   on the neck of the CRT.
 
 Don't expect high bandwidth, uniform response, or any of the other
   things you take for granted with a decent scope. That takes work.
   However, as a fun project, this certainly qualifies. Interchanging
   the functions of the horizontal and vertical deflection yoke (and
   rotating it 90 degrees) may provide a better match of horizontal
   and vertical bandwidth to your intended applications or experiments.
 
 SAFETY: Once you disconnect the deflection yoke from the TV or monitor's
   circuits, move the original circuits out of the way and put a barrier
   between between you and the rest of the TV or monitor. All you will need are
   connections to the deflection yoke on the CRT (unless you want to do
   intensity modulation). With a color TV or monitor, such experiments
   could be pretty interesting but there may be color fringing effects
   since you are not compensating for certain aspects of dynamic convergence
   at all.
15.9) Displaying a video signal as a picture on an oscilloscope
 
I am not sure why anyone would really want to do this other than as an
experiment - it would be interesting one.
 
If a composite video signal is the input, you will need a sync separator.
 
You will have to construct a vertical deflection voltage ramp generator
which can be locked to your vertical sync signal.
 
The horizontal timebase of the scope will be fine for the horizontal
deflection and should easily lock to your horizontal sync pulse or
(if the scope has a TV trigger mode) directly to the video signal.
 
A video amplifier will be needed if your Z axis does not have an internal
amplifier (you need .7 V p-p to be full brightness range.) Unless you provide
automatic gain control, this will need to include offset (brightness)
and gain (contrast) adjustments. Even if there is an internal amplifier, it
may not have the required bandwidth for the video signal.
 
However, the overall brightness may be disappointing - a scope is not designed
for overall high brightness. The beam focus will not be as good as that on
a little TV either.
 
15.10) Use of surge suppressors and line filters
 
Should you always use a surge suppressor outlet strip or line circuit?
Sure, it shouldn't hurt. Just don't depend on these to provide protection
under all circumstances. Some are better than others and the marketing
blurb is at best of little help in making an informed selection. Product
literature - unless it is backed up by testing from a reputable lab - is
usually pretty useless and often confusing.
 
Line filters can also be useful if power in you area is noisy or prone
to spikes or dips.
 
However, keep in mind that most well designed electronic equipment
already includes both surge suppressors like MOVs as well as L-C
line filters. More is not necessarily better but may move the point
of failure to a readily accessible outlet strip rather than the innards
of your equipment if damage occurs.
 
Very effective protection is possible through the use of a UPS (Uninterruptible
Power Supply) which always runs the equipment off its battery from the internal
invertor (not all do). This provides very effective isolation power line
problems as the battery acts as a huge capacitor. If something is damaged,
it will likely be the UPS and not your expensive equipment. Another option
is to use a constant voltage transformer (SOLA) which provides voltage
regulation, line conditioning, and isolation from power spikes and surges.
 
It is still best to unplug everything if the air raid sirens go off or
you see an elephant wearing thick glasses running through the neighborhood
(or an impending lightening storm).
 
15.11) GFCI tripping with monitor (or other high tech equipment)
 
Ground Fault Circuit Interrupters (GFCIs) are very important for
minimizing shock hazards in kitchens, bathrooms, outdoors and other
potentially wet areas. They are now generally required by the NEC Code
in these locations. However, what the GFCI detects to protect people - an
imbalance in the currents in the Hot and Neutral wires caused possibly
by someone touching a live conductor - may exist safely by design in
high tech electronic equipment. The result - false tripping - is
mostly a problem with 3 wire grounded devices with built in line filters
having capacitors between Hot and Ground but may also occur with 2 wire
ungrounded TVs due to the power-on surge into the highly capacitive
or inductive loads of their power supplies.
 
15.12) Multisystem TVs
 
The question often arise: can my NTSC TV modified to display PAL signals
(or vice-versa). Unlike a VCR where there are substantial differences
between recording of NTSC and PAL, the problem of displaying the picture
is much simpler.
 
The following assumes 525 line NTSC and 625 line PAL:
 
The horizontal scan rates are nearly identical (15,734 Hz for NTSC and
15,625 Hz for PAL), so this is not likely to be a problem. If these
differed significantly, then there would be design issues similar to
those for multisync computer monitors and this would drive up cost.
 
The vertical scan are slightly more of a problem with 525 line/60 Hz
NTSC and 625 line/50 Hz PAL. But it is a lot easier to design vertical
deflection to accommodate a modest variation in rates. TVs could be easily
designed or modified to accept either.
 
The color encoding techniques differ but inexpensive ICs exist that
can deal with either standard. In fact, many are programmable to
do either with a jumper and slight modifications to the external
components.
 
Displaying a monochrome - B/W - picture on the other kind of
set is usually possible if the set has a vertical hold control
or enough vertical range. Modifying the chroma circuitry is
more complicated but it should be possible to substitute a
second IC and patch it into the existing video chain.
 
As far as commercial multisystem TVs are concerned, the real reason we
do not see many of these (at least in the U.S.) is lack of demand. They
are available if you look hard enough and are willing to pay a premium.
They are readily available on the international market.
 
15.13) Could a TV be modified for 3D (stereo) display?
 
The whole idea of stereo 3-D vision to put the left and right views to the
appropriate eyeball. There are two common ways of doing this:
 
 Use different colors for the two views with color filters in from of
   each eye to separate the views. This is what were often used for
   the really bad (content wise) sci-fi movies of the '50s.
 
 Display alternate views on the same monitor screen but use LCD shutter
   glasses to allow each eye to only see the appropriate view. This requires
   increasing the refresh rate to avoid unacceptable flicker.
The first approach can be used with any TV and a pair of monochrome
video cameras. Of course, true color cannot be used since pure colored
images are needed to separate the stereo views.
 
Alternating views with synchronized LCD glasses is a possibility but
on a standard TV, the resulting refresh rate would be 30 Hz with a 50%
duty cycle which is likely to be useful only as a short experiment - else
your viewers will likely develop splitting headaches.
 
15.14) Displaying TV on a computer monitor
 
My general recommendation is that if you have the space, buy an inexpensive
TV - the quality in the end may in fact be better. And, it will be usable
without tying up your expensive monitor and (maybe) PC.
 
While various convertors are advertized to use a computer monitor
with video from a VCR or other source, keep in mind that if it sounds
too good to be true, it probably is like the claim of a $200 box for this:
 
OK, let me get this straight - this card/box will enable a 31.4 KHz horizontal
scan rate monitor (VGA) be used as a TV - yes or no? It thus includes a video
A/D, full screen frame buffer, D/A, and all the other tuner stuff for under
$200? I don't think so. A scan doubler - which is a subset of the above -
will not result in a high quality picture since it will display pairs of
lines interleaved. Or does the impressive advertisement leave out the
key requirement that the monitor sync at the NTSC horizontal scan rate
of 15.734 KHz (most newer monitor do not)? Or is it a board that plugs
into a PC and indeed does use the resources of the PC including the VGA
card and bus?
 
In any case, get a written money back satisfaction guarantee.
 
15.15) Displaying computer video on a TV
 
Assuming this means NTSC:
 
 You need to convert RGB to NTSC - there are single chips for this. Try
   Sony, Philips, Motorola, and others. These will combine the R, G, B,
   H sync, and V sync into a single composite video signal using a minimum
   of additional components.
 
 You need to match the scan rate to NTSC - 15.734 KHz horizontal. Even
   basic VGA is twice this - 31.4 KHz. If your video card can be programmed
   to put out interlaced NTSC rate video then this is easy. If not, it is
   more difficult. If you want to use anything higher res than VGA, it is
   a very non-trivial problem requiring the construction of a scan convertor
   which includes a video A/D, full frame store, interpolator/readout timing,
   video D/A. Unless you are an experienced digital/analog designer, you
   really do not want to tackle any of this.
For the special case of VGA->NTSC, you may be able to get away with just
storing a single scan line since the horizontal frequency is (almost)
exactly twice the NTSC horizontal of 15.734 KHz. A double buffer where
one buffer is storing while the other is reading out at approximately half
the VGA pixel rate should work. With appropriate timing, even lines become the
even field for NTSC and odd lines become the odd field (I may have this
backwards). It is still not a trivial undertaking. Also, keep in mind
that the quality you will get on NTSC will be poorer than the VGA due to
fundamental NTSC bandwidth limitations. Also, flicker for line graphics will
be significant due to the interlacing at 30 Hz. Even this is a non-trivial
undertaking.
 
The requirements for PAL are very similar. For 625 lines systems, the
800x600 is the format that most closely matches the TV resolution.
 
You can also buy little boxes to do this. Quality is general not great
as you are seriously limited by NTSC/PAL and the VCR. Except for
presentations on existing TV rate equipment, it is probably not worth
the effort. This is totally useless for any serious computer applications.
 
For professional presentations, modern video projectors are available that
use high resolution LCD panels and real-time scan conversion. However,
they are quite expensive (up to $10,000!!!).
 
15.16) What is Kell factor with respect to interlaced displays?
 
(The following is from Bob Myers (myers@fc.hp.com)).
 
The Kell factor - which has to do with the fact that we're often undersampling
an image from the standpoint of the Gospel According to St. Nyquist - IS
a factor in the reduction of vertical resolution, but interlacing plays
a part as well. This comes from at least two factors:
 
 The receiver usually cannot precisely interleave the two fields.
 
 More importantly, there are steps taken to reduce the interline flicker
   which reduce the effective vertical resolution. This includes running the
   line width of the display somewhat larger than would otherwise be the case,
   and in interlaced cameras, discharging the entire screen (including the
   lines from the other field) after every field scanned.
Interlace is particularly troublesome on moving images, where you will often
perceive momentarily missing details. There was a LOT of discussion
regarding the gory details of interlacing in the recent HDTV debates within
SMPTE and other groups.
 
15.17) Homemade V-chip (or at least viewing limiter
 
Here is an interesting questions:
 
I would like a control box of some sort that controls the
cable signal that comes into the TV. I want to be able to
control the total time a particular child has in his account to
watch, plus the actual channels that he is allowed to watch
(no Playboy or MTV), PLUS the time of day that he can watch
(not during home work time). Programmable by channel,
cumulative time, hour of the day, and day of the week. I also
need a master pass word for parental programming of the kids
accounts, plus be able to watch what I want to at any time.
The kids could use either an individual account number or an
individual card of some kind with a PIN like our ATM cards.
This box should be secure so that a 14 year old boy can't
bypass it very easily. At least without doing come major damage
so that I'd know it when he did it. I know that this is a lot
to ask, but I'm very familiar with computer programming and
chipset technology, I do know that such a thing can be done. I
just don't have the electronics knowledge to do it.
The following probably won't help you build such a gizmo but here
are some thoughts:
 
First, I would not attempt to build any of the RF/cable switching
stuff - there are too many variations. I would suggest trying to
control the control of what you have. With a cable box, this would be
relatively easy - just put the box and an IR transmitter in the same
sealed enclosure. If you have only a cable ready TV, you could substitute
or intercept the remote detector signal inside the set and disable
the front panel controls.
 
Then you need:
 
 An input devices - keypad for example.
 A display - a 1 line LCD.
 A microprocessor. This doesn't need to be much - just to store the
  'account information' including balance, allowable channel and time
  slot map, passwords. It would need a real time clock.
 An IR remote code transmitter. This could probably be directly
  programmed by the micro to control your cable box.
 
Each account would have a means of adding to the balance,
password authentication, etc.
 
You would have a superuser account for your own watching as well as
changing any of the individual account settings.
 
Too bad I don't still teach my intro to computer design courses - this
would make a nice term project.
 
If you have a junker PC, this would be a simple bit of programming
(but quite wasteful of power even for an 8088 based PC).
 
15.18) Interesting TV Switch Mode Power Supply
 
The following was found in a Sony TV:
 
                      Q1 switching/reg
                         transistor
               (+) ---
            ----+-------------| |---------+-----------|
      ---- | | --- | _|_
AC ---| |--| = C1 | | diode /_\ D2
in ---| |------|---| +-----+------+ | |
      ---- (-) | | Reg. Drive | C |
       D1 | +-----+------+ C choke +---- gnd
                    | | C _|_
                    | | | +135 cap ___ C2
                    | | | I---> |+
                    +----------+----------+-----------+---- + 135
Although at first this appears to short out the line supply, when
drawn like this it turns out to be a valid switching regulator:
 
Q1 is driven by a pulse width modulated signal a the horizontal rate.
 
Q1 turns on putting 150 V across choke. Current ramps up in choke - more or
   less linear until saturation which should not occur. This time increases
   with increasing load.
 
Q1 turns off. Since current in an inductor cannot change instantly, current
   continues to flow, now through D2, C2, and +135 load. LCR (R of load,
   diode) time constant - charges capacitor and powers load.
 
It would appear to fail and run away under the following circumstances:
 
 Inductance is too low and choke cannot store enough energy even at high duty
   cycle to supply load. Too high a duty cycle and core saturates at which
   point transistor blows up.
 
 Inductance is too high relative to switching frequency so that choke
   does not have time to discharge (its current) before next current pulse -
   DC current will just keep increasing until core saturates. This could only
   really happen if the switching frequency were too high for some reason
   unless someone changed core material or something like t.
 
 Load is too great due to fault elsewhere.
When attempting to diagnose problems with these types of circuits where the
natural outcome of a fault is for one or more expensive parts to fail
catastrophically, it is wise to either use a Variac to bring up the input
voltage slowly and carefully observe the behavior hopefully before too late
or put a load in series with the line such as a 100W light bulb to limit
the current (though this will change the behavior in various ways).
15.19) IR detector circuit
This IR Detector may be used for testing of IR remote controls, CD player
laserdiodes, and other low level near IR emitters.
Component values are not critical. Purchase photodiode sensitive to near
IR - 750-900 um or salvage from optocoupler or photosensor. Dead computer
mice, not the furry kind, usually contain IR sensitive photodiodes. For
convenience, use a 9V battery for power. Even a weak one will work fine.
Construct so that LED does not illuminate the photodiode!
The detected signal may be monitored at the collector of the transistor (Q1)
with an oscilloscope.
 Vcc (+9 V) >-------+---------+
                    | |
                    | \
                    / / R3
                    \ R1 \ 500
                    / 3.3K /
                    \ __|__
                    | _\_/_ LED1 Visible LED
                  __|__ |
        IR ----> _/_\_ PD1 +--------> Scope monitor point
          Sensor | |
        Photodiode | B |/ C
                    +-------| Q1 2N3904
                    | |\ E
                    \ |
                    / R2 +--------> GND
                    \ 27K |
                    / |
                    | |
       GND >--------+---------+
                   _|_
                    -
Chapter 16) International Color Television Standards
 
16.1) Some questions and answers about TV standards
 
(Responses from: Steve McKinty: (smckinty@france.sun.com))
 
Q: What are the most common TV standards in the world?
 
NTSC
National Television Standards Committee
PAL
Phase Alternate Line
SECAM
SEquential Couleur Avec Memoire (Sequential colour with memory)
There are other differences though. Strictly they are just different
colour systems, but most countries which use PAL have 625 lines in
a picture and send 25 full pictures/second, most NTSC countries have
525 lines and send 30 full pictures/second (mostly for historical
rather than technical reasons). That complicates things.
Q: Who devised them, and when? and why? Are they as old as television?
 
The first serious TV experimenting was done in several countries around
the period 1900-1930, mostly black & white. The BBC started a regular
service in 1936, other countries followed soon after, but since the
technology was developing very rapidly there were always improvements
being made. The BBC started with 405 lines, the US started a service
a couple of years later with 525, by the time other European countries
started the technology allowed 625 lines. France even tried 819 lines.
 
All those system were black & white, but people wanted to have
colour. During the 1940's much of Europe was at war, and technological
development for entertainment slowed down, but in the US they
were able to continue and devised a colour system which was
compatible with the existing black & white one.
 
By compatible I mean that a black & white TV got a black & white
picture, a colo(u)r one got a colour picture. No need to make people
throw away their B&W TVs. This system was endorsed by the American
National Television Standards Committee, and was named after it => NTSC.
 
After the war other countries started to look at colour. NTSC was a
very clever system, but it had some flaws. Engineers in various
countries tried to improve on it, and Telefunken in Germany came up
with a simple modification which improved colour stability. It
was named PAL because they reversed the Phase of the colour signal on
Alternate Lines.
 
At the same time Henri de France, in France, fixed the same flaw in
a different way. His design (SECAM) needed a memory inside the set
which made it more expensive. PAL gave as good a result, so most
countries opted for that. France stayed with SECAM, possibly because
in the De Gaulle era of the 50's memories of German occupation were
still fresh, and dropping a French system in favour of a German one
would have been unpopular. Rumour has it that the French government
subsidized Thompson to make memory affordable.
 
Since Britain went PAL, France went SECAM, and the US went NTSC, any
colonies or dependencies of those countries tended to get the same
system. India/Pakistan got PAL, Algeria got SECAM, and since the
US helped rebuild Japan after WW2 it got NTSC, etc.
Q: What's the difference?
 
To squeeze a colour signal into the same space as a black & white one,
and stay compatible, the NTSC designers separated the colour and
brightness information. The human eye is less sensitive to colour, so
they were able to reduce the bandwidth of that signal (make it take
up less space in each channel), 'hiding' it at the high-frequency
end of the video. That meant they didn't need to make the channels
bigger, and incompatible.
 
To do that, they used the fact that you can represent most colours
with a combination of Red, Green and Blue. If you film a scene
with three cameras, one for each colour, then add all the
outputs together you get a black & white image. This signal
is called luminance, usually represented by 'Y'. Mathematically
Y = R + G + B. (Actually, not all the contributions are equal).
 
They then transmitted the Y signal just as for a black & white TV,
and also transmitted the R and B in the extra colour signal. B&W TV's
only saw Y, and colour TV's got Y, R and B. Since Y = R + B + G, G can
be obtained as Y - (R+B), so they didn't need to transmit all three.
 
To get both R and B into one signal, they use a combination of
Phase and Amplitude modulation (think of it as AM and FM at the same
time). Its called quadrature modulation, and works very well, but is
susceptible to phase changes as it passes along cables, etc. If the
signal gets +10 degrees phase change the colour will visibly change,
which is why NTSC TV's have a tint control.
 
PAL overcomes that by sending R and +B on one line, then R and -B on
the next. That way a +10 phase shift on one line becomes -10 on the next,
and small differences will cancel out. PAL TV's don't need tint controls.
 
SECAM doesn't send both R & B together, it sends R on one line, B on
the next. No fancy modulation, so no phase problems, but you need a
'memory' in the set to save up the signal from the previous line,
since both R & B are required together for processing.
 
Q: Why do you need different TVs?
 
Mostly because of the different numbers of lines. Its quite easy to
make one colour decoder which can cope with all the systems, but
making a TV which can do 625 and 525 lines, 25 and 30 pictures/second,
gets expensive. Consumers shop on price, no-one will buy a SECAM
TV in the USA even if it only costs $20 more, since there aren't
any SECAM channels.
Q: Why do you need different VCRs?
Q: Why can't one VCR record the same output?
 
Some can, but like TVs it costs more to make them adjust. The motor
speed varies with the number of pictures transmitted per second, for
example. (This is covered in more detail in the document:
Notes on the Diagnosis and Repair of Video Cassette Recorder (VCR)
Notes on the VCR Failure Diagnosis and Repair.)
 
Q: Why did different systems evolve?
Q: Is one cheaper?
Q: Is one better?
 
When originally developed, expense was considered based on contemporary
technology. As noted, politics may have been equally important.
 
As to which has better quality, its all rather subjective. The
625-line system adopted in Europe has better vertical resolution
than the 525-line US system, but some people find the 50Hz field rate
still produces some flicker. NTSC/PAL/SECAM are all equally capable
of excellent colour reproduction, but under poor signal conditions
NTSC can degrade more quickly.
Q: Are there other systems besides the ones I've mentioned? Why?
 
Some others, like MAC where the colour and luminance are completely
separated. That gets rid of interference (ever see the strange
colours which appear on very fine check patterns?) but is more
expensive and really only possible due to modern electronics.
 
Q: Are there going to be more or less systems in the future?
 
That is THE question! There are certainly going to be different
systems, more lines, better sound, etc.
 
Q: Is there any way to convert a PAL tape to NTSC or vice versa?
 
Yes. If the PAL tape has 625 line pictures and the NTSC one has 525 line
then you normally need a computer which can read in one format and
re-adjust things. Not cheap, but becoming cheaper, several companies
offer that sort of service. Some PAL VCRs can do a half-conversion,
enough to fool most PAL TVs into thinking its got a PAL signal.
 
Q: Do they teach this stuff in electrical engineering courses?
 
Sometimes. Some of it, depends a lot on the course and school.
16.2) Politically Correct TV Standards
 
(The following is from: Robert Rolf).
 
SECAM
Used by France and the former Soviet union.
          No tint control. No color control.
          Full socialism. The state knows exactly what color you
          should see, and how strong that color should be.
PAL
Used by Germany & UK, Australia etc.
          No tint control. A color control.
          Partial socialism. The state knows exactly what color you
          should see, but you get a choice as to how strong it can be.
NTSC
Used in USA and Canada, Japan etc.
          A tint control, A color control.
          Uncontrolled socialism. The state lets you chose what color you
          see and how strong it can be. They then tax you regardless.
Just another way of looking at it....
16.3) Variations on a 'standard' - the PAL system
 
In the U.S., when PAL is mentioned, it is usually assumed to be 625 line/50 Hz
as used in the UK and man other places. However, there are several variations
on the PAL system.
 
(The following from: Ed Ellers <edellers@delphi.com))
I can think of five major groups right off:
PAL B/G/H
625-line 50 Hz systems used in most European countries and many
countries in Africa, the Middle East and Asia.
PAL I
Again 625 lines at 50 Hz, but with a different sound carrier
frequency. Used in the United Kingdom, the Republic of Ireland, Hong Kong,
South Africa and a few other places I've forgotten.
PAL D/K
Yet another 625-line system with a different sound carrier. Used in
some former Warsaw Pact countries as well as mainland China; this may become
more popular as PAL/SECAM receivers become common in the CIS republics and
other former Soviet bloc countries, since those countries now use SECAM D/K.
PAL M
This one's 525 lines at 59.94 Hz; it's just like NTSC except for
PAL-type color encoding. It's used mainly in Brazil.
PAL N
A real oddity, with 625-line 50 Hz video but a LOWER sound carrier
and a lower color subcarrier than the B/G/H, I and D/K varieties. It's used
in Argentina and a few other places.
16.4) Color television standards worldwide
 
(The following is from EDMUNDO, Design Engineer Ten-Lab)
 
We at Ten-Lab have put together the following chart listing countries
and their corresponding color TV standards.
 
We are trying to be as accurate as possible, but we need your feedback to
refine and correct the information. We are doing the best we can in spite
of inherent problems such as:
 
 Some of the literature and charts are contradictory;
     even some books and manuals contradict each other more than they agree.
 
 Many countries have changed their names during the last few years.
 
 Some countries have one broadcast TV system, but also receive programs in a
   different system from beyond their borders. This creates some confusion
   about the format(s) used locally.
INTERNATIONAL TV STANDARDS CHART by TEN-LAB (UPDATED Jan 19, 1996)
COUNTRY VHF STANDARD UHF STANDARD
 
AFGANISTAN PAL/SECAM B
ALBANIA PAL B PAL G
ALGERIA PAL B PAL G
ANGOLA PAL I
ARGENTINA PAL N PAL N
AUSTRALIA PAL B PAL G
AUSTRIA PAL B PAL G
AZORES PAL B
BAHAMAS NTSC M
BAHRAIN PAL B PAL G
BANGLADESH PAL B
BARBADOS NTSC M
BELGIUM PAL B PAL H
BERMUDA NTSC M
BOLIVIA NTSC M
BOTSWANA PAL I
BOURKINA FASO SECAM K1
BRAZIL PAL M PAL M
BRUNEI PAL B
BULGARIA SECAM D SECAM K
BURMA NTSC M
BURUNDI SECAM K1
CAMBODIA NTSC M
CAMEROON PAL B PAL G
CANADA NTSC M NTSC M
CANARY ISLANDS PAL B
CHAD SECAM K1
CHILE NTSC M NTSC M
CHINA PAL D
COLOMBIA NTSC M NTSC M
COSTA RICA NTSC M NTSC M
CUBA NTSC M NTSC M
CYPRUS PAL G PAL G
CZECHOSLOVAKIA: now
  CZECH REPUBLIC PAL PAL
  SLOVAK REPUBLIC PAL PAL
DAHOMEY SECAM K1
DENMARK PAL B PAL G
DJIBHOUTI SECAM B SECAM G
DOMINICAN REP NTSC M NTSC M
ECUADOR NTSC M NTSC M
EGYPT SECAM B SECAM G
EL SALVADOR NTSC M NTSC M
EQUATORIAL GUINEA PAL B
ETHIOPIA PAL B PAL G
FIJI PAL B
FINLAND PAL B PAL G
FRANCE SECAM L SECAM L
FRENCH POLYNESIA K1
GABON SECAM K1
GAMBIA PAL I
GERMANY PAL B PAL G
GHANA PAL B PAL G
GIBRALTAR PAL B PAL H
GREECE SECAM/PAL B SECAM/PAL G
GREENLAND NTSC M/PAL B
GUADELOUPE SECAM K1
GUAM NTSC M
GUATEMALA NTSC M NTSC M
GUANA (FRENCH) SECAM K1
GUINEA PAL K
HONDURAS NTSC M NTSC M
HONG KONG PAL I
HUNGARY SECAM D/PAL SECAM K/PAL
ICELAND PAL B PAL G
INDIA PAL B
INDONESIA PAL B PAL G
IRAN SECAM B SECAM G
IRAQ SECAM B
IRELAND PAL I PAL I
ISRAEL PAL B PAL G
ITALY PAL B PAL G
IVORY COAST SECAM K1
JAMAICA NTSC M
JAPAN NTSC M NTSC M
JORDAN PAL B PAL G
KENYA PAL B PAL G
KOREA NORTH SECAM D
KOREA SOUTH NTSC M NTSC M
KUWAIT PAL B
LEBANON SECAM B SECAM G
LIBERIA PAL B PAL H
LIBYA SECAM B SECAM G
LUXEMBOURG PAL B PAL G/SECAM L
MADAGASCAR SECAM K1
MADEIRA PAL B
MALAGASY SECAM K1
MALAWI PAL B PAL G
MALAYSIA PAL B
MALI SECAM K1
MALTA PAL B PAL H
MARTINIQUE SECAM K1
MAURITANIA SECAM B
MAURITIUS SECAM B
MEXICO NTSC M NTSC M
MONACO SECAM L
MONGOLIA SECAM D
MOROCCO SECAM B
MOZAMBIQUE PAL B
NAMIBIA PAL I
NEPAL PAL B
NETHERLANDS PAL B PAL G
NETH. ANTILLES NTSC M NTSC M
NEW CALEDONIA SECAM K1
NEW GUINEA PAL B PAL G
NEW ZEALAND PAL B PAL G
NICARAGUA NTSC M NTSC M
NIGER SECAM K1
NIGERIA PAL B PAL G
NORWAY PAL B PAL G
OMAN PAL B PAL G
PAKISTAN PAL B
PANAMA NTSC M NTSC M
PARAGUAY PAL N
PERU NTSC M NTSC M
PHILIPPINES NTSC M NTSC M
POLAND SECAM D/PAL SECAM K/PAL
PORTUGAL PAL B PAL G
PUERTO RICO NTSC M NTSC M
QATAR PAL B
REUNION SECAM K1
RUMANIA PAL D PAL K
RUSSIA SECAM D SECAM K
RWANDA SECAM K1
SABAH/SARAWAK PAL B
ST. KITTS NTSC M NTSC M
SAMOA NTSC M
SAUDI ARABIA SECAM B/PAL B SECAM G
SENEGAL SECAM K1
SEYCHELLES PAL B PAL G
SIERRA LEONE PAL B PAL G
SINGAPORE PAL B PAL G
SOMALIA PAL B PAL G
SOUTH AFRICA PAL I PAL I
SPAIN PAL B PAL G
SRI LANKA PAL B
SUDAN PAL B PAL G
SURINAM NTSC M NTSC M
SWAZILAND PAL B PAL G
SWEDEN PAL B PAL G
SWITZERLAND PAL B PAL G
SYRIA SECAM B
TAHITI SECAM K1
TAIWAN NTSC M NTSC M
TANZANIA PAL B PAL B
THAILAND PAL B
TOGO SECAM K
TRINIDAD Y TOBAGO NTSC M NTSC M
TUNISIA SECAM B
TURKEY PAL B PAL G
UGANDA PAL B PAL G
UNITED ARAB EMIRATES PAL B PAL G
UNITED KINGDOM PAL I
UPPER VOLTA SECAM K1
URUGUAY PAL N PAL N
USA NTSC M NTSC M
VENEZUELA NTSC M NTSC M
VIETNAM PAL B PAL G
YEMEN PAL B
YUGOSLAVIA PAL B PAL G
ZAIRE SECAM K1
ZAMBIA PAL B PAL G
ZIMBABWE PAL B PAL G
16.5) Cable channel allocation
 
(The following is from: (kruskal@watson.ibm.com (Vincent Kruskal)).
 
The following table gives the definitions of the numeric cable channels
defined in the EIA (Electronic Industries Association) Interim
Standards, IS-6 (CP), May 1983 and associated information that has been
gathered. Definitions appear at the end.
           HRC
         Picture
Channel Carrier Cable Band Other Names
-------- ------- ----------- --------------------------
    1 72 MHz Low (VAR) A-8, C54, J54, G64, 4+, 5A
    2 54 Low
    3 60 Low
    4 66 Low
    5 78 Low A-7, C55, J55, G65
    6 84 Low A-6, C56, J56, G66
 
    7 174 High
    8 180 High
    9 186 High
   10 192 High
   11 198 High
   12 204 High
   13 210 High
 
   14 120 Mid A
   15 126 Mid (ATC) B
   16 132 Mid (ATC) C
   17 138 Mid (VAR) D
   18 144 Mid (VAR) E
   19 150 Mid (VAR) F
   20 156 Mid (VAR) G
   21 162 Mid (VAR) H
   22 168 Mid (VAR) I
   23 216 Super (VAR) J
   24 222 Super (VAR) K
   25 228 Super L
   26 234 Super M
   27 240 Super N
   28 246 Super O
   29 252 Super P
   30 258 Super Q
   31 264 Super R
   32 270 Super S
   33 276 Super T
   34 282 Super U
   35 288 Super V
   36 294 Super W
   37 300 Hyper AA, W+1
   38 306 Hyper BB, W+2
   39 312 Hyper CC, W+3
   40 318 Hyper DD, W+4
   41 324 Hyper EE, W+5
   42 330 Hyper FF, W+6
   43 336 Hyper GG, W+7
   44 342 Hyper HH, W+8
   45 348 Hyper II, W+9
   46 354 Hyper JJ, W+10
   47 360 Hyper KK, W+11
   48 366 Hyper LL, W+12
   49 372 Hyper MM, W+13
   50 378 Hyper NN, W+14
   51 384 Hyper OO, W+15
   52 390 Hyper PP, W+16
   53 396 Hyper QQ, W+17
   54 402 Hyper RR, W+18, C62
   55 408 Hyper SS, W+19, C63
   56 414 Hyper TT, W+20, C64
   57 420 Hyper (HAM) UU, W+21, C65
   58 426 Hyper (HAM) VV, W+22, C66
   59 432 Hyper (HAM) WW, W+23, C67
   60 438 Hyper (HAM) AAA, W+24, C68
   61 444 Hyper (HAM) BBB, W+25, C69
   62 450 Hyper (HAM) CCC, W+26, C70
   63 456 Hyper DDD, W+27, C71
   64 462 Hyper EEE, W+28
   65 468 Ultra U14, FFF, W+29
   66 474 Ultra U15, GGG, W+30
   67 480 Ultra U16, HHH, W+31
   68 486 Ultra U17, III, W+32
   69 492 Ultra U18, JJJ, W+33
   70 498 Ultra U19, KKK, W+34
   71 504 Ultra U20, LLL, W+35
   72 510 Ultra U21, MMM, W+36
   73 516 Ultra U22, NNN, W+37
   74 522 Ultra U23, OOO, W+38
   75 528 Ultra U24, PPP, W+39
   76 534 Ultra U25, QQQ, W+40
   77 540 Ultra U26, RRR, W+41
   78 546 Ultra U27, SSS, W+42
   79 552 Ultra U28, TTT, W+43
   80 558 Ultra U29, UUU, W+44
   81 564 Ultra U30, VVV, W+45
   82 570 Ultra U31, WWW, W+46
   83 576 Ultra U32, AAAA, W+47
   84 582 Ultra U33, BBBB, W+48
   85 588 Ultra U34, CCCC, W+49
   86 594 Ultra U35, DDDD, W+50
   87 600 Ultra U36, EEEE, W+51
   88 606 Ultra (RA) U37, FFFF, W+52
   89 612 Ultra U38, GGGG, W+53
   90 618 Ultra U39, HHHH, W+54
   91 624 Ultra U40, IIII, W+55
   92 630 Ultra U41, JJJJ, W+56
   93 636 Ultra U42, KKKK, W+57
   94 642 Ultra U43, LLLL, W+58
   95 90 Low (FM) A-5, C57, J57
   96 96 Low (FM) A-4, C58, J58
   97 102 Low (FM) A-3, C59, J59
   98 108 Low A-2, C60, J60, G60
   99 114 Low A-1, C61, J61, G61
  100 648 Ultra U44, MMMM, W+59
  101 654 Ultra U45, NNNN, W+60
  102 660 Ultra U46, OOOO, W+61
  103 666 Ultra U47, PPPP, W+62
  104 672 Ultra U48, QQQQ, W+63
  105 678 Ultra U49, RRRR, W+64
  106 684 Ultra U50, SSSS, W+65
  107 690 Ultra U51, TTTT, W+66
  108 696 Ultra U52, UUUU, W+67
  109 702 Ultra U53, VVVV, W+68
  110 708 Ultra U54, WWWW, W+69
  111 714 Ultra U55, AAAAA, W+70
  112 720 Ultra U56, BBBBB, W+71
  113 726 Ultra U57, CCCCC, W+72
  114 732 Ultra U58, DDDDD, W+73
  115 738 Ultra U59, EEEEE, W+74
  116 744 Ultra U60, FFFFF, W+75
  117 750 Ultra U61, GGGGG, W+76
  118 756 Ultra U62, HHHHH, W+77
  119 762 Ultra U63, IIIII, W+78
  120 768 Ultra U64, JJJJJ, W+79
  121 774 Ultra U65, KKKKK, W+80
  122 780 Ultra U66, LLLLL, W+81
  123 786 Ultra U67, MMMMM, W+82
  124 792 Ultra U68, NNNNN, W+83
  125 798 Ultra U69, OOOOO, W+84
16.6) Notes on cable and broadcast frequencies
 
(The following is from: kruskal@watson.ibm.com (Vincent Kruskal)).
 
RF band
To get the band, subtract 1.25 from picture carrier (low end)
and add 4.75 (high end).
 
Color subcarrier
Add 3.58... to picture carrier.
 
Sound carrier:
Add 4.5 to picture carrier.
 
HRC
Harmonically Related Carrier. Makes both second- and third-order
beats invisible by making them fall directly on the picture carrier of
other channels. That is, multiplying the picture carrier by two or
three will yield exactly another picture carrier.
 
IRC
Incrementally Related Carrier, add 1.25 to HRC frequency. A
General Instruments (Jerrold) catalog said that IRC makes third-order
(more important than second-order) beats invisible by making them fall
directly on the picture carrier of other channels. But it is not true
that multiplying an IRC picture carrier by two or three yields another
IRC picture carrier. This contradiction has not been resolved. The
reason third-order harmonics are more important is that oscillators and
amplifiers tend to generate odd-order harmonics far more than even-order
ones.
 
Broadcast frequency
Add 1.25 to HRC frequency except for channels 5 and
6. For them, subtract 0.75. But these are just nominal frequencies.
The FCC actually has three channel designations for each number as in 5,
5- and 5+. The minus channels are 10 kHz below the nominal value and
the plus channels are 10 kHz above. For example: (next section)
16.7) Why is the NTSC color subcarrier such a weird frequency?
 
(The following if from Bob Myers (myers@fc.hp.com)).
 
Actually, if we wanted to define the rates to the Nth degree, the
important starting point is the field rate. The NTSC color frame rate
was defined as (60 * 1000/1001) Hz, which is a bit more than 59.94 Hz.
From this rate, all the others in the system are defined. The line rate
is 262.5 times this, and the color subcarrier is defined as 455/2 times the
line rate. This is often given as simply 3.579545 MHz, but the the
color subcarrier was actually derived from the line/field rates rather
than the other way around.
 
The whole thing was done so as to avoid (or at least minimize) interaction
between the luminance, chrominance, and audio subcomponents in the
standard color signal. This could have been achieved by moving either
the audio subcarrier or adjusting the line/frame rates as described above;
unfortunately, the latter route was chosen, leaving us with this very
strange-looking set of rates.
 
The precise color burst frequency winds up being 3.579545.4545... under
this definition, but giving it to the nearest Hz is within the tolerances
of the system.
 
16.8) What is the maximal allowed deviation of the horizontal frequency?
 
(The following is from: Peter Bennett VE7CEI (bennett@triumf.ca))
 
In Canada and the US (525 line, 60 HZ, NTSC), the horizontal frequency is
15,734.264 Hz. The colour subcarrier is 455/2 times the horizontal
frequency which should come to 3.579545 MHz. I believe the tolerance on
the subcarrier frequency is +/- 10 Hz.
 
16.9) Informal comparison of TV standards
 
Q: I heard that TV in certain part of Europe has more quality in
Europe then here in North America. I'd like to know the differences between
the two systems. Is that why we cant use video tapes from there?
 
(Responses from: Mark Zenier (mzenier@netcom.com or mzenier@eskimo.com))
 
The first difference is that a lot of the world runs on 50 Hz power
as opposed to North America's 60 Hz power. In the olden days, before
active power supply regulators got cheap, it was decided that the
vertical scan rate match the power supply frequency, so that ripple
in the power supply wouldn't produce obnoxious visual effects.
 
So the PAL/SECAM signals have 50 vertical scans per second.
 
I don't know the exact reasoning, but the horizontal scan rate is
close to the same. 15750 (now 15734) for 60 Hz, and 15625 for 50 Hz
systems. My guess is the tradeoff between cost (50 years or so ago)
and audibility for a large portion of the population.
 
So 50 Hz systems have more lines - 625 vs. 525 lines for
60 Hz systems.
 
The second difference is that European TV channels are wider. 7 or 8 MHz
compared to the North American 6 MHz. Video bandwidth is limited to
4.2 MHz in a 6 MHz channel, but can be as much as 6 MHz in some of the
50 Hz systems. (NOTE: Systems is plural. There are many different
European systems with incompatible color and sound transmission methods.)
 
As for the quality, if you move a little farther away, so that a pixel
on each system subtends the same angle, NTSC doesn't have a poorer
picture, just a smaller one.
 
Chapter 17) Repair Information and Parts Sources
 
17.1) Advanced TV troubleshooting
 
If the solutions to your problems have not been covered in this document,
you still have some options other than surrendering your TV to the local
service center or the dumpster.
 
(Also see the related document:
Sources of Repair Information and General Comments.)
 
Manufacturer's service literature
Service manuals are available
for a great deal of consumer electronics. Once you have exhausted the
obvious possibilities, the cost may be well worth it. Depending on the
type of equipment, these can range in price from $10-50 or more. Some
are more useful than others. However, not all include the schematics so
if you are hoping to repair an electronic problem try to check before buying.
 
Inside cover of the equipment:
TVs often have some kind of circuit
diagram pasted inside the back cover. In the old days, this was
a complete schematic. Now, if one exists at all, it just shows part
numbers and location for key components - still very useful. Some
TVs - as late as 10 years ago, maybe even now - included a complete
schematic with the product information and owner's manual. I have a
1984 Mitsubishi which has this. It is, however, the exception rather
than the rule anymore.
 
SAMs Photofacts
These have been published for over 45 years (I don't
know for how long but I have SAMs for a 1949 portable (3 inch) Pilot TV -
about as portable as an office typewriter (if you remember what one of
those was like) and are generally the best most consistent source
of service info for TVs (nearly every model that has ever been sold),
radios, some VCRs and other consumer electronics. For TV servicing,
they are indispensable.
There are some Computerfacts but the number of these is very limited.
The VCRfacts are also somewhat limited and the newer ones tend to have
strictly mechanical information.
 
SAMs are often available (for photocopy costs) from you local large
public library which may subscribe to the complete series. If not,
a large electronic distributor can order the selected folder for you.
 
One advantage of the SAMs info is that it is compiled in a very
consistent format so that once you are familiar with one model TV,
it is easy to transfer that knowledge to any other. They provide
waveforms at key locations and DC voltage measurements almost
everywhere. Additional info such as IC pin to ground and coil
resistances are often provided as well. The manufacturer's service
manuals are generally not nearly as complete.
 
(BTW, I have no connection with SAMs.)
 
17.2) Service manuals for really old TVs
 
Try your large public library for SAMs photofacts. I found a 3 TV of
from around 1948 at a yard save. There was no problem finding a complete
manual including schematics, parts list, troubleshooting procedures, etc.
Someday, I may even get around to fixing it. All the paper capacitors are
leaky (for starters).
 
BTW, the case for this 3 TV is about 18 x 10 x 15
and it includes a handy option: a 6 inch semispherical water filled
magnifier. The CRT is an oscilloscope tube. Not your basic portable!
 
17.3) Parts information
 
I have found one of the most useful single sources for general
information on semiconductors to be the ECG Semiconductors Master
Replacement Guide, about $6 from your local Philips distributor.
STK, NTE, and others have similar manuals. The ECG manual will
enable you to look up U.S., foreign, and manufacturer 'house' numbers
and identify device type, pinout, and other information. Note that
I am not necessarily recommending using ECG (or other generic) replacements
if the original replacements are (1) readily available and (2) reasonably
priced. However, the cross reference can save countless hours searching
through databooks or contacting the manufacturers. Even if you have
a wall of databooks, this source is invaluable. A couple of caveats:
(1) ECG crosses have been known to be incorrect - the specifications
of the ECG replacement part were inferior to the original. (2) Don't
assume that the specifications provided for the ECG part are identical
to the original - they may be better in some ways. Thus, using the ECG
to determine the specifications of the parts in your junk bin can be
risky.
 
Other cross reference guides are available from the parts source
listed below.
 
17.4) Information sources on the Internet
 
Many manufacturers are now providing extensive information via the
World Wide Web. The answer to you question may be a mouse click
away. Perform a net search or just try to guess the manufacturer's
home page address. The most obvious is often correct. It will usually
be of the form http://www.xxx.com where xxx is the manufacturers' name,
abbreviation, or acronym. For example, Hewlett Packard is hp, Sun
Microsystems is sun, Motorola is, you guessed it, motorola. Electronic
parts manufacturers often have detailed datasheets for their product
offerings.
 
17.5) Suggested references
A good source for technology information is Basic Theory of Colour
Television from Philips. Ask this book from your local technical bookstore.
(The following from: (xtarelex@powergrid.electriciti.com))
For a technical reference on the various flavours of NTSC, PAL, and SECAM
used around the world, I suggest:
Recommendations and reports of the CCIR, volume XI, part 1
Available from Omnicom, 115 Park St. S.E. Vienna, VA 22180 (703)281-1135
There don't seem to be nearly as many TV repair books for modern solid
state TVs as I recall for old tube sets. Here are is one suggestion
which you may find (or its predecessor) at your local public library
(621.384 if you library is numbered that way) or a technical book store.
MCM Electronics has this as well.
 
Troubleshooting and Repairing Solid State TVs
Homer L. Davidson
2nd Edition, 1992
TAB Books, Inc.
Blue Ridge Summit, PA 17214
17.6) Interchangeability of components
 
Q: If I cannot obtain an exact replacement or if I have a monitor, TV, or
other equipment carcass gathering dust, can I substitute a part that is not
a precise match?
Sometimes, this is simply desired to confirm a diagnosis and avoid the risk of
ordering an expensive replacement and/or having to wait until it arrives.
 
For safety related items, the answer is generally NO - an exact replacement
part is needed to maintain the specifications within acceptable limits with
respect to line isolation, X-ray protection and to minimize fire hazards.
Typical parts of this type include flameproof resistors, some types of
capacitors, and specific parts dealing with CRT high voltage regulation.
However, during testing, it is usually acceptable to substitute electrically
equivalent parts on a temporary basis. For example, an ordinary 1 ohm
resistor can be substituted for an open 1 ohm flameproof resistor to determine
if there are other problems in the horizontal deflection circuits before
placing an order - as long as you don't get lazy and neglect to install the
proper type before buttoning up the monitor or TV.
 
For other components, whether a not quite identical substitute will work
reliably or at all depends on many factors. Some deflection circuits are
so carefully matched to a specific horizontal output transistor that no
substitute will be reliable.
 
Here are some guidelines:
 
 Fuses - exact same current rating and at least equal voltage rating.
   I have often soldered a normal 3AG size fuse onto a smaller blown 20 mm
   long fuse as a substitute.
Resistors, capacitors, inductors, diodes, switches, potentiometers, LEDs, and other common parts
 - except for those specifically marked as
   safety-critical - substitution as long as the replacement part fits
   and specifications should be fine. It is best to use the same type - metal
   film resistor, for example. But for testing, even this is not a hard
   and fast rule and a carbon resistor should work just fine.
 
 Rectifiers - many are of these are high efficiency and/or fast recovery
   types. Replacements should have at equal or better PRV, Imax, and Tr
   specifications.
 
 Transistors and thyristors (except HOTs and SMPS choppers) - substitutes
   will generally work as long as their specifications meet or exceed those
   of the original. For testing, it is usually ok to use types that do not
   quite meet all of these as long as the breakdown voltage and maximum
   current specifications are not exceeded. However, performance may not
   be quite as good. For power types, make sure to use a heatsink.
 
 Horizontal output (or SMPS) transistors - exact replacement is generally
   best but except for very high performance monitors, generic HOTs that
   have specifications that are at least as good will work in many cases.
   Make sure the replacement transistor has an internal damper diode if
   the original had one. For testing with a series light bulb, even a
   transistor that doesn't quite meet specifications should work well
   enough (and not blow up) to enable you to determine what else may be
   faulty. The most critical parameters are Vceo/Vcbo, Ic, and Hfe which
   should all be at least equal to the original transistor. I have often
   used by favorite BU208D as a temporary substitute for other HOTs and SMPS
   (chopper) transistors. Make sure you use a heatsink and thermal grease
   in any case - even if you have to hang the assembly by a cable tie to
   make it fit.
 
 Deflection yokes - in the old days, particularly for TVs, all of these
   were quite similar. It was common to just swap with one that fit
   physically and at most need to adjust or change a width coil. With
   high performance multiscan monitors, this is no longer the case. Sometimes
   it will work but other times the power supply won't even be able to come
   up as a result of the impedance mismatch due different coils and pole
   piece configurations. In addition, there may be other geometry correction
   coils associated with the yoke that could differ substantially.
 
 CRTs - aside from the issues of physical size and mounting, many factors
   need to be considered. These include deflection angle, neck diameter,
   base pinout, focus and screen voltage requirements, purity and convergence
   magnets, etc. Color CRT replacement is rarely worth the effort in any
   case but trying to substitute a different CRT is asking for frustration.
   For monochrome CRTs, there is less variation and this may be worth a try.
 
 The following are usually custom parts and substitution of something from
   your junk box is unlikely to be successful even for testing: flyback (LOPT)
   and SMPS transformers, interstage coils or transformers, microcontrollers,
   and other custom programmed chips.
17.7) Repair parts sources:
 
For general electronic components like resistors and capacitors, most
electronics distributors will have a sufficient variety at reasonable
cost. Even Radio Shack can be considered in a pinch.
 
However, for consumer electronics equipment repairs, places like Digikey,
Allied, and Newark do not have the a variety of Japanese semiconductors
like ICs and transistors or any components like flyback transformers or
degauss Posistors.
 
The following are good sources for consumer electronics replacement parts,
especially for VCRs, TVs, and other audio and video equipment:
 
MCM Electronics (VCR parts, Japanese semiconductors,
U.S. Voice: 1-800-543-4330. tools, test equipment, audio, consumer
U.S. Fax: 1-513-434-6959. electronics including microwave oven parts
     and electric range elements, etc.)
 
Dalbani (Excellent Japanese semiconductor source,
U.S. Voice: 1-800-325-2264. VCR parts, other consumer electronics,
U.S. Fax: 1-305-594-6588. Xenon flash tubes, car stereo, CATV).
Int. Voice: 1-305-716-0947.
Int. Fax: 1-305-716-9719.
 
Premium Parts (Very complete VCR parts, some tools, adapter
U.S. Voice: 1-800-558-9572. cables, other replacement parts.)
U.S. Fax: 1-800-887-2727.
 
Computer Component Source (Mostly computer monitor replacement parts,
U.S. Voice: 1-800-356-1227. also, some electronic components including
U.S. Fax: 1-800-926-2062. semiconductors.)
Int. Voice: 1-516-496-8780.
Int. Fax: 1-516-496-8784.



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