Notes On The Troubleshooting And Repair Of Television Sets


  28.23) So you lost your original remote (or it fell in the toilet)

An exact replacement remote will be easiest to use but may do significant
harm to your bank account.

For example, you cannot add or remove channels from a typical Sony TV using
the common universal remotes.

(From: Ed Ellers (edellers@delphi.com)).

Universal Electronics' "One For All" remote controls can reproduce these
codes, and any others on any Sony TV (among others).  Typically you'd press
[MAGIC] and then 1-9-4 to add a channel or 1-9-0 to erase one; to start the
auto program mode you'd press [MAGIC] and then 1-2-4.

  28.24) 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.....

  28.25) 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!

  28.26) Sweet little old ladies and TVs from attic

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

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

1. 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.

2. Increased resistance or inductance of the yoke windings.  For all
   you know, the yoke may have been replaced with the wrong part.

3. Yoke improperly positioned on tube neck.

4. Excessive high Voltage.  This is usually not adjustable.

I bet the thing hasn't worked properly in 10 years.

  28.27) Phantom spot or blob on CRT after set is shut off

(Portions of the following from a video engineer at Philips.)

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).

A broad diffused glow (not a distinct spot in the middle of the screen)
that lasts for a few seconds to minutes is called 'afterglow' and may be
considered 'normal' for your model.  The warm CRT cathodes continue to
emit electrons due to the high voltage that is still present even though
the signal circuits may have ceased to operate.

For more sharply defined spots there are two phenomena:

1. Thermal emission from a cathode that has not yet cooled off (and this
   could take several minutes) gives a more or less circular spot near the
   centre.  It is actually 3 spots from the 3 cathodes, we at Philips call
   them 'Christmas balls'.

2. Field emission from sharp whiskers on any electron gun part gives a much
   sharper spot, sometimes with a moon-shaped halo around it.  Even with the
   filament off, there may be some electron emission from these sharp points
   on the cold cathode(s) 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.

The shape of the spot is an inverted image of the shape of the emitting
area(s) on the electron guns cathodes.

The visibility of both effects depends in the same way on the decay time of
the high voltage (HV/EHT) on the anode.

When turned off with the remote or front panel 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 or longer 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 may be present
for long enough to keep the brightness (and beam current) up and drain the
HV quickly.  Whether this actually happens depends on many factors - often
not dealt with by the designers of the set.

A proper design (who knows, yours may simply have been broken from day 1 or
simply be typical of your model) 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.

In most sets it is left to chance whether the picture tube capacitance will
be discharged by beam current at switch-off.  It may simply be due to the
behaviour of the video control IC when its supply voltage drops that causes
the cathodes to be driven to white and this may not be formally specified by
the manufacturer of the IC.  Some of of the latest sets have an explicit
circuit to discharge the EHT at shutdown.

As noted in the section: "Safety guidelines" the HV charge on the CRT
capacitance can be present for a long time.  A service technician should
be very aware of that before touching HV parts!

Interestingly, most sets for the Asian Pacific market have a bleeder resistor
built in that will discharge the EHT without the need for a white flash at
switch-off.  These will in fact drive the beam to black at switch-off via a
negative voltage to the CRT G1 electrode.  The AP market is very sensitive
to proper set behaviour, they don't like a white flash.

In short, it all depends on the demands of the particular market, the chance
of the picture tube producing a spot/blob, and the mood of the designer.

So, 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.  This is usually not a problem with
direct view TVs but would definitely be a concern with high intensity
projection tubes.

On the other hand, your phantom blob may provide for some interesting
conversation at your next party!

  28.28) 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?  Sucked in?  What does one do with an unwanted 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 shadow mask will have many sharp edges if it is broken.

In addition, there could be a nice surprise awaiting anyone disconnecting the
high voltage 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!

  28.29) Shock and/or spark when connecting cable or other A/V components

TVs with hot chassis - where signal ground is actually line connected and
at some intermediate (and dangerous) voltage - will have an isolation block
in between the tuner and antenna/cable connections.  TVs with isolated power
supplies may have some bypass capacitors between the power supply and signal
grounds (including the A/V shields if there are A/V connectors).  It is
possible for a failure to result in a serious safety hazard where the RF
(antenna/cable) or A/V connectors become electrically live.

However, a tingle or small spark might be normal.  RFI bypass caps between the
AC input and shield on the connector could result in some leakage - 50 V or
more might be indicated using a high impedance multimeter.  This is harmless.
Reversing the plug in the AC socket (if it is not polarized or if you are using
an unpolarized extension cord) might eliminate or greatly reduce the effect.

Nonetheless, it should be checked out.  Measure the resistance between each
side of the AC plug and the RF and AV connector shields.  It should be 1 M ohm
or more.  Test for voltage between the cable (or other device) connector and
earth ground.  If there is anything significant, test the resistance on the
device between its shield and its power plug as above - other devices may have
RFI bypass caps or be defective as well.

  28.30) What is the deal with Macrovision copy protection?

(From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)).

JVC owns the patent for VHS. JVC has made a deal with Macrovision that from 
a certain date in the past *no* VHS recorder licenced by JVC shall be able 
to record any video signal that contains Macrovision's copy protection 
pulses. Any video recorder from before that date (VHS or other) might
well work OK on the altered video signal ! The copy protection pulses 
upset the video-AGC and H-sync. TV's usually don't have a video-AGC.
The stabilizer box removes the extra pulses and makes it into a normal 
video signal again. No VCR should ever know the difference, so they 
should all record properly again.

At the same time, all TV's are required to ignore the copy protection
pulses. As a TV-designer I can tell you that this is sometimes far from
trivial. Not in the least because in the beginning we were not included
in "the deal". There may be TV's around whose brightness and/or sync will 
be disturbed by the Macrovision pulses. Officially, this is the reason
for existance of the stabilizer boxes: to view better, not to copy better.
Unofficially, they are sold for copying, of course.

The next step will be that digital-TV decoders will output an analog TV
signal with Macrovision copy-protection pulses so that you may watch but 
not record your pay-per-view program. Same problem, same solution ...

And I thought that PAL/Secam/NTSC were *standards*, sigh ...

Whether they like it or not (and from personal experience I can tell you that
we don't like it) it is the responsibility of the TV set-maker (in your case
Sony) to build a TV that takes the Macrovision copy protection pulses without
showing any side effects on the screen.  Seems like they didn't do a good job
on your TV :-). But they will have to fix this, your complaint is valid. I
think in this case it may be the dealer's responsibility too, maybe you can
trade it for a different brand ? And do try it out first ...

Sadly, more complex TV's seem to suffer more than the simpler, old-fashioned,
designs. Unfortunately, Macrovision seems to be satisfied when their pulses
do not affect the majority of (mostly older) TV's.  In your Sony TV, the
clamping circuit seems to be affected by some ultra-black pulses in the signal.
Maybe an anti-Macrovision decoder can help you, officially they are designed
for *this* purpose.

  28.31) AGC and copy protection

(From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)).

1. RF-AGC which compensates for different signal strength at the aerial,
   it measures RF amplitude and is *not* sensitive to video contents
   because with negative modulation the sync is the peak and is constant,
   this AGC will not work on CVBS (baseband video) inputs.

2. Video-AGC which normalizes baseband signals which enter *after* the
   tuner-IF. A.o. this compensates for different signal strengths when
   you connect two VCRs together. It measures peak-white, so it *is*
   sensitive to video content and thus to the Macrovision pulses.

And: a television does NOT have a video-AGC, unless you want to call the beam
current limiter circuits an AGC.  (Exception: the Secam-L system with positive
modulation requires an RF-AGC which measures peak-white instead of peak-sync.)
The RF-AGC does not see the peak-white of the anti-copy pulses.
If you connect the VCR to the TV via the CVBS (baseband) input, then
the RF-AGC is not even in the path. Still, it may be disturbed.
But the sync separator may see the extra inserted Hsync pulses, and
due to the phase disturbance the video clamping may be disturbed too.

  28.32) On-screen clock runs slow or fast

You will need the Sams' Photofact for the set.

If the clock reference is power line derived, noisy power can sometimes
result in erratic timekeeping though running fast is probably more common
than running slow.  This could be a result of a lamp dimmer or compact
fluorescent on the same circuit.

If it has a separate crystal for the time keeping, that could be faulty.

Now think about it: Do you absolutely need the TV's clock???  After all, there
are probably a half dozen other clocks in the same room!

  28.33) Cold problems with cold TVs - or - an unhappy Christmas

(From: Ren Tescher (ren@rap.ucar.edu)).

My Christmas repair story wasn't so happy.

I worked as TV repairman for an appliance store.

On a very cold (20 below zero Fahrenheit) evening a man bought a new 25"
console for the family.

As we loaded it into the back of their pickup truck, we *told* them.  "Do not
plug this in until it warms back up to room temperature."  They nodded and
said "uh-huh, okay".

They lived about 15 minutes away.

25 minutes later we get a telephone call...

"Hey! that TV you sold us don't work!"

So we ended up loading another TV into our delivery van, drove out to their
place.  Unloaded it, and WAITED until the thing was warm enough to plug in.

Needless to say, I got home late that Christmas Eve and had brand new TV
console waiting for my repair back at the shop.

Chapter 29) Some Model Specific Problems

  29.1) Erratic problems with older GE TVs

Older GE TVs used double sided circuit boards with poor-man's vias - rivets
soldered to the traces top and bottom.  These have been called 'Rivlets' and
'Griplets'.  Unfortunately, whoever did the design didn't realize that (1) the
the rivets did not heat adequately during soldering and (2) the expansion
coefficients of the rivets and circuit board were not qutie identical.

Thus, erratic problems are almost a certainty with these TVs.  Normal logical
troubleshooting is useless.  The only solution is to repair every !@#$ Griplet
on all circuit boards in the TV.

I have repaired these with a high power soldering gun used on both sides with
liberal application of solder and flux.  However, I do not recommend this
shortcut unless you are willing to redo the repair every couple of years.

(From: Mr. Caldwell (jcaldwel@iquest.net)).

There are two methods of repair.

* Method 1: Clean the paint from around each griplet on both sides of the
  board to expose the surrounding copper pad. Apply liquid solder flux to the
  cleaned copper.  Solder so as to bridge the griplet to the cleaned copper.

* Method 2: Do the above but desolder the griplet and place a wire through it
  so that the wire extends beyond the griplet to the copper foil and solder
  the wire on both sides (this was the final fix GE used in this chassis).

If done carefully Method 1 works and is reliable.

I would normally do this prior to any troubleshooting, it repairs most problems
in this chassis. While you have the board out working on it be sure to also
clean and resolder high temperature components and connections that look bad.
These griplets can be on all boards, even the tuner control board.

  29.2) Erratic problems on late model GE, RCA, or ProScan TV

Problems with bad solder connections, mostly in and around the tuner are very
common with several series of late model (e.g., CTC175/176/177 chassis)
RCA/GE/Proscan TVs.  Ignoring these erratic and intermittent problems can lead
to serious damage including failure of the EEPROM and possibly other expensive
ICs.  Therefore, it is essential to deal with the solder connections as soon
as these symptoms appear.  The repairs are straightforward though perhaps
tedious.  Thompson may reimburse for reasonable cost of repairs.

Some of the common symptoms include:

    * Random power cycling.  It may come on in the middle of the night!
    * Picture shifts or changes size vertically or horizontally.
    * Picture turns to snow or shows other reception problems.
    * Picture turns to random display of time or other data.
    * Noisy or muted sound, volume buttons have no effect.
    * Remote has no or unexpected effect.

See the document: "RCA/GE CTC175/176/177 Tuner Repair" for additional
information on these types problems including repair procedures and
approaches to getting coverage from Thompson Electronics.

  29.3) Sylvania/Magnavox/Philips - no startup

Check the resistor supplying initial base current to the horizontal driver
(not HOT) transistor.  On many chassis, it is R502, 47 K.  It opens for not
good reason.  Why it fails is a mystery as its power rating should be adequate.

  29.4) Sony TVs/monitors and Hstat

Symptoms are that the TV or monitor will shut down possibly after a warmpup
period.  There can be other causes but failure of the Hstat module HV sense
wire is quite likely on many Sony models.

(From: Mr. Beanz (slin01@mail.orion.org)).

If you've determined that the HV is fine, and the H-STAT is shutting
down for no reason, it's possible to bypass.  There is a little brown
wire coming out the bottom of the H-STAT which goes to a 3-pin
connector.  Two wires have a jumper, and the brown wire goes to the
other.  Snip the brown wire at the H-STAT and the TV will continue to
function normally.  Measuring the regulated B+ to the flyback will give
you a pretty good indication of the condition of the HV output.  If it
remains steady at rated voltage (I forget what it was, 130V or 135V)
then HV is A-OK.  If it slowly creeps up or is too high to begin with,
you have a problem.  The voltage will normally jump to 150V or so after
HV shutdown is tripped.

Ideally, you should replace the H-STAT in this case.  Although taking
the poor man's route will WORK, you lose any protection in the event
that the HV circuitry should malfunction.

  29.5) More on Hstat

(From: Shawn Lin (slin01@mail.orion.org or lin@science.smsu.edu)).

The H-STAT is a plastic box that sits mounted to the picture tube's
shield.  It's red in color (for every SONY TV that I have owned) and has
a single knob on it.  The flyback's HV output wire goes into the H-STAT
and another HV wire exists the H-STAT and connects to the anode cap on
the picture tube.  It has a dual purpose, horizontal static convergence
(the control adjusts this) and HV overvoltage shutdown protection. 
Chances are, your HV is within spec and the H-STAT is bad, but you
should make sure the regulated voltage to the flyback is steady and
doesn't fluctuate before assuming the H-STAT is bad.

H-STAT is expensive, and may not be worth replacing.  My KV-1952RS is old and
as a whole, not worth the cost of a new H-STAT, so I just bypassed it and
didn't bother replacing it.  The TV's been working great for over a year and
the picture is still excellent.

Note: On some models, the sense wires need to be connected during startup
or else it will never come on.

CAUTION: On some monitors (like the Sony CPD1302), the sense signal may be
used for actual HV regulation.  Thus, if the sense wire is disconnected, (or
the divider inside the Hstat block fails open) there is no feedback and it is
possible for the high voltage (and probably B+) to increase until the HOT
(and possible other components) blow.  I do not know if this applies to Sony
built TVs as well.

Chapter 30) Items of Interest

  30.1) 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 

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.

  30.2) What is this goop around some electrolytic capacitors and other components?

That goop is probably glue and generally harmless - it is there to hold
down the components aganst vibration.  I have heard of it sometimes
decomposing and shorting stuff out but I doubt you have that problem.

Therefore, unless you find a bad cap in the focus or related circuit, we
are still looking at a flyback problem.

  30.3) What does the flyback (LOPT) transformer do?

The typical flyback or Line OutPut Transformer (LOPT) consists of two parts:

1. A special transformer which in conjunction with the horizontal output
   transistor/deflection circuits boosts the B+ (120 V typical for a TV) of the
   low voltage power supply to the 20 to 30 KV for the CRT as well as provide
   various secondary lower voltages for other circuits.

   A HV rectifier turns the high voltage pulses into DC and the CRT capacitance
   smooths it.  The HV may be developed from a single winding with many many
   turns of wire or a lower voltage winding and a diode-capacitor voltage

   The various secondary voltages power the logic, tuner, video signal,
   vertical deflection circuits, and CRT filament.  In fact, with many TV
   designs, the only power not derived from the flyback is for the keep-alive
   circuitry needed to maintain channel memory and provide startup drive to
   the horizontal deflection/high voltage system.

2. A voltage divider that provides the focus and screen supplies.  The pots
   are in this divider network - and these things fail resulting poor focus,
   uncontrolled brightness, or fluctuating focus and/or brightness.  A
   total short could also result in failure of other components like
   the horizontal output transistor.  In some TVs, the focus and screen
   divider and/or controls are external to the flyback and susceptible
   to dust and problems particularly on humid days.  The resistance of these
   circuits is so high that dirt or other contamination can easily provide
   a bypass path to ground especially when slightly damp.

  30.4) Why do flyback (LOPT) transformers fail?

While flyback transformers can on occasion be blown due to a failure elsewhere
in the TV or monitor's power supply or deflection circuits, in most cases,
they simply expire on their own.  Why?

Flybacks are wound with many layers of really really fine wire with really
really thin insulation.  This entire assembly is potted with an Epoxy resin
which is poured in and allowed to cure.

In some ways, these are just short circuits waiting to happen.

Flybacks get hot during use and this leads to deterioration of the insulation.
Any imperfections, nicks, scratches, etc. in the insulation contributes to
failure.  Temperature cycles and manufacturing defects result in fine cracks
in the Epoxy potting material reducing the insulation breakdown particularly
in the area of the high voltage windings, rectifiers, and focus/screen divider

It is amazing they last as long as they do with the stress they are under.
They also physically vibrate to some extent.  A whole bunch of other factors
are also no doubt important.

  30.5) Brief comments on testing the HOT

For a TV with no blown fuses that will not start, here are two quicky
checks to see if the HOT is good and has power and drive:

* HOT tests - check across each pair of pins for shorts (preferably removed
  from the circuit board).  No junction should measure less than 50 ohms
  or so.  Lower readings almost certainly indicate a bad HOT.  If in-circuit,
  however, the reading between base and emitter will be near zero due to the
  secondary of the driver transformer.  See the document: "Testing Diodes and
  Bipolar Transistors with a DMM or VOM".  Don't be confused by internal
  damper diodes and B-E resistors.

* Power - measure across the collector to emitter with a multimeter (with
  the HOT removed or if there is no deflection, this is safe with it in
  place).  There should be solid B+ - typically about 100 to 160 V (115
  VAC sets - possibly higher for 220 VAC sets).  If this is missing, iether
  there is a problem with the power supply or the emitter fusable resistor
  has blown (probably in addition to the HOT) and there is no return.

* Drive: put an oscilloscope on the base - there should be pulses around
  .7 V for most of the scan (~50 microseconds) and probably going negative
  a couple volts at least for retrace (~12 microseconds).  If drive is weak
  or missing, determine how startup is implemented as there may be a problem
  in the startup power supply or deflection IC.

WARNING: use an isolation transformer for the oscilloscope tests (and whenever
you are probing a TV in general)!!!  This part of the circuit, in particular,
is usually line connected.  See the sections on safety.

  30.6) CRT rejuvenation

Where one or more electron guns in the CRT have deteriorated due to wear and
tear, it is sometimes possible to give them a new, but possibly, temporary
lease on life through rejuvenation using a special piece of CRT service

(From: Gary Klechowitz (klechowi@execpc.com)).

When I rejuvenate a tube I inform the customer that there is no warranty on
the job.  Rejuvenating a CRT is like when Clatuu was brought back to life by
Gort in "The Day The Earth Stood Still". When asked "How long will you live"?
he replied: "no one knows".

I use a Sencore Beam Builder. If your tube is just moderately dim and blurry
but still shows good cut off threshold, I would just use the auto restore mode
on the beam builder rather than using the restore button. If the tube is
really bad with little or no cutoff threshold, then the rejuvenator is needed
but that has less than a 50% chance of fixing the tube and in many cases the
tube gets worse to trashed in the process.

  30.7) 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.

  30.8) How does Picture-In-Picture (PIP) work?

A separate video input or tuner provides the PIP baseband signal which is then
resized and stored in a frame buffer large enough to hold the X and Y
dimensions of the PIP image.  Readout is timed to place the PIP image in the
selected area of the screen and it is substituted for the main video.  What
could be simpler?!

Go to [Next] segment
Go to [Previous] segment

Go to [Table 'O Contents]

Written by Samuel M. Goldwasser. | [mailto]. The most recent version is available on the WWW server http://www.repairfaq.org/ [Copyright] [Disclaimer]