Notes On The Troubleshooting And Repair Of Television Sets


  22.23) 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.

Since they function as fuses, flameproof resistors should not be replaced
with higher wattage types unless specifically allowed by the manufacturer.
These would not blow at the same level of overload possibly resulting in
damage to other parts of the circuitry and increasing the risk of fire.

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.

  22.24) Width and height change with warmup

Since both width and height are affected, this points to something common
like the low voltage power supply.  If there are any indications of hum
bars, first check the main filter capacitor(s) or substitute a known
good one.  There might even be other symptoms like faint retrace lines
on at least part of the screen.

Start by monitoring the B+ to the flyback (feeding the HOT) to see if this
drifts at all.  If it does, then there is probably a low voltage regulator
problem - bad capacitor, resistor, or chip.  Use freeze spray to narrow
it down.  If this is solid, then there could be a high voltage drift but
this would be somewhat unusual without other symptoms (like arcing) since
the HV is nearly always tracks the low voltage supply.

  22.25) Problems with SCR based regulators

"Sharp TV has a short blast of high voltage and sound then shuts down. All
 components in regulator area test good. I have two of these sets."
 Is there a good sharp tech out there thats seen this problem?"

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

There is a bulletin from Sharp on troubleshooting *any* SCR regulated TV, this
can easily be adapted to RCA, GE, Emerson and Panasonic sets that have similar 
circuits given a little thought but the technician.

You are going to need to figure part of this out as I no longer have the
schematics available. All this will do is allow you to rule out either the
regulator or the horizontal section. 

Don't plug this in until you've read the whole list.

Figure out how to bypass the turn on circuit from the microprocessor (unless
it's a manual one).  This is usually just jumpering the relay but sometimes
Sharp puts a horizontal Vcc turn on transistor that also must be jumpered.

Next jumper across the SCR anode to cathode.

Now using an *variable isolation transformer* turn the voltage on it down and
plug the set in.  Bring the voltage up slowly, if you can bring the AC up so
that the DC on the jumper across the SCR is within the regulated voltage you
should have a  picture and this rules out the horizontal section as the

If the set shuts down prior to getting the DC up enough then you've got 
problems in the horizontal section. Either you have something wrong with the
high voltage transformer or the tuning caps or there is a problem with the
x-ray protect pick off voltage to the deflection IC. 

If it's the horizontal section you can set the AC at approx. 25v and look at 
the waveforms in the horizontal output section for defects like ringing.

I've never gotten a good troubleshooting technique down for the regulator
since it's an active circuit the waveforms and voltages are not stable when 
it's failed. A good diode, transistor and capacitor checker will help.

It would help to get the  service manual for that set, the training manual
for that chassis and the bulletin dealing with troubleshooting SCR regulators.

Also the training manual should have a good explanation of how this 
regulator works. In a nutshell the regulator is a switched mode circuit 
that uses a winding from the high voltage transformer to turn off the SCR.
The regulator is always turned off at the same time by a pulse from the 
high voltage transformer. Regulation is achieved by controlling when the 
SCR is allowed to turn on.

  22.26) TV shuts down with dark picture or when changing channels

This may happen at any time or possibly after being on for awhile in which
something heats up and drifts out of spec.

The low voltage regulator may be letting the voltage rise excessively.  Then,
a dark picture or video muting during a channel change triggers the X-ray
or power supply overvoltage protection.

Monitor the output of the low voltage power supply B+ to see if it is stable
as the brightness/scene changes.

Chapter 23) Deflection Problems

  23.1) Deflection fundamentals

Note: the following is just a brief introduction.  For more detailed deflection
system theory of operationo and sample circuits, see the document: "TV and
Monitor Deflection Systems".

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

For NTSC and PAL, the vertical scan rates are 60 and 50 Hz (approximately)

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:

1. Sync separator to obtain horizontal and vertical synchronization pulses.

2. Horizontal oscillator which locks to horizontal sync pulses.

3. 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.

4. Vertical oscillator which locks to vertical sync pulses.  Yoke requires
   sawtooth waveform for linear vertical deflection.

5. Vertical drive/output which feeds vertical deflection yoke.  Newer TVs
   use ICs for vertical drive and output.

6. 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.

  23.2) About the vertical scan rate

Some people believe that the TV scan rate is locked to the local power line.
TVs never ever used the line frequency for vertical rate.  The vertical rate
is not even equal to line frequency, actually 59.94 Hz (NTSC).  It was set
originally to 60 Hz to minimize the visibility of interference between the
deflection and power transformer.  When NTSC added color, it changed to
59.94 Hz for highly technical reasons.  And, TVs no longer have power

  23.3) 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

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.

  23.4) 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:

1) Power is failing to the horizontal output transistor - this could be
   due to a low voltage power supply problem, bad connection, etc.

2) Base drive to the horizontal output transistor is failing - could be a
   fault in the horizontal oscillator or bad connection.

3) Problem with the flyback transformer or its secondary loads (flyback
   may provide other power voltages).

4. 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.

  23.5) 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

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.

  23.6) Insufficient width (without hum bars)

If there are hum bars or wiggles in the picture and/or hum in the sound, see
the section: "Reduced width picture and/or hum bars in picture and/or hum in sound".

If both width and height are affected, the cause is likely something common:
low, low voltage power supply voltages or excessive high voltage (resulting
in a 'stiffer' beam).

(From: Jerry G. (jerryg@total.net)).

Lack of width is usually caused by defective power supply, low horizontal
drive to the yoke and flyback, defective circuits in the pincushioning
amplifier section, excessive high-voltage caused by defective voltage
regulation, and or excessive loading on the secondary side of the flyback.

  23.7) Vertical lock lost

This indicates a picture that is correct but rolling vertically.

If the picture is rolling down the screen the frequency of the vertical
oscillator is incorrect - too high - and this may be the problem.  Generally,
the free run frequency of the vertical oscillator should be a little below
the video rate (of around 50 or 60 Hz depending on where you live).

If it is rolling continuously without jumping, then there is a loss of
sync from the sync separator or faulty components in the vertical oscillator
causing it to totally ignore the sync pulses.

If it is rolling up rapidly and not quite able to remain locked, the free
run frequency may be too low or there could be a fault in the sync circuits
resulting in an inadequate vertical pull-in range.

On older sets, there was actually a vertical hold (and possibly even a
separate vertical frequency) control.  On anything made in the last decade,
this is unlikely.  There may be Vertical Frequency and Vertical Pull-in
Range adjustments (and others) accessible via the service menu.  However,
if any of these ever change, it indicates a possible problem with the EEPROM
losing its memory as component drift is unlikely.

As with everything else, bad connections are possible as well.  You will need
a schematic and possibly setup info to go beyond this.

  23.8) Vertical squashed

This is a vertical deflection problem - possibly a bad capacitor, bad
connection, flyback/pumpup diode, or other component.  None of these should
be very expensive (in a relative sort of way).

If the symptoms change - particularly if they become less severe - as the set
warms up, a dried up electrolytic capacitor is most likely.  If they get
worse, it could be a bad semiconductor.  Freeze spray or a heat gun may be
useful in identifying the defective component.

It is often easiest to substitute 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

A defective deflection yoke is also possible or in rare cases, a bad yoke
damping resistor (e.g., 500 ohms, may be mounted on the yoke assembly itself).

The following are NOT possible: CRT, flyback, tuner (except for the famous
RCA/GE/Proscan or Sony models where the controller is at fault - see the
sections on these specific brands).  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.

  23.9) 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.

  23.10) Single Vertical Line

CAUTION: To prevent damage to the CRT phosphors, immediately turn down the
brightness so the line is just barely visible.  If the user controls do not
have enough range, you will have to locate and adjust the master brightness or
screen/G2 pots.

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.

  23.11) Single Horizontal Line

CAUTION: To prevent damage to the CRT phosphors, immediately turn down the
brightness so the line is just barely visible.  If the user controls do not
have enough range, you will have to locate and adjust the master brightness or
screen/G2 pots.

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:

1. 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.

2. 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.

3. 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.

4. Other bad parts in vertical deflection circuit though there are not
   that many parts that would kill the deflection entirely.

5. Loss of power to vertical deflection circuits.  Check for blown
   fusable resistors/fuses and bad connections.

6. Loss of vertical oscillator or vertical drive signals.

The most likely possibilities are in the deflection output stage or
bad connections to the yoke.

  23.12) Keystone shaped picture

This means that the size of the picture is not constant from top to bottom
(width changes) or left to right (height changes).  Note that some slight
amount of keystoning is probably just within the manufacturing tolerance of
the deflection yoke and factory setup (geometry magnet placement, if any).  On
a TV, this is only noticeable with scenes having straight edges (e.g., video
games) in relationship to the CRT bezel.

However, a sudden increase (and it will usually be rather substantial in a
TV) may indicate a problem with the deflection yoke.

An open or short in a winding (or any associated components mounted on the yoke
assembly) will result in the beam being deflected less strongly on the side
where that winding is located.  Typical TV yokes have fewer individual windings
in parallel than high scan rate monitors so the effects of one such fault are
more dramatic.  See the section: "Deflection yoke testing".

If the set has been dropped off a 20 story building, the yoke may have shifted
its position on the neck, of the CRT resulting in all sorts of geometry and
convergence problems (at the very least).

  23.13) 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.

  23.14) 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.

  23.15) Horizontal output transistors keep blowing (or excessively hot)

Unfortunately, these sorts of problems are often difficult to definitively
diagnose and repair and will often involve expensive component swapping.

You have just replaced an obviously blown (shorted) horizontal output
transistor (HOT) and an hour (or a minute) later the same symptoms
appear.  Or, you notice that the new HOT is hotter than expected:

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:

1. Improper drive to horizontal output transistor (HOT).  A weak drive might
   cause the HOT to turn on or (more likely) shut off too slowly (greatly
   increasing heat dissipation.  Check driver and HOT base circuit components.
   Dried up capacitors, open resistors or chokes, bad connections, or a driver
   transformer with shorted windings can all affect drive waveforms.

2. Excessive voltage on HOT collector - check LV regulator (and line
   voltage if this is a field repair), if any.

3. Defective safety capacitors or damper diode around HOT.  (Though
   this usually results in instant destruction with little heating).

4. New transistor not mounted properly to heat sink - probably needs mica
   washer and heat sink compound.

5. 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 if properly mounted to the heat sink (using
heatsink compound).  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.

  23.16) Horizontal output transistors blowing at random intervals

The HOT may last a few months or years but then blow again.

These are among the hardest problems to locate. It could even be some peculiar
combination of user cockpit error - customer abuse - that you will never
identify.  Yes, this should not happen with a properly designed monitor.
However, a combination of mode switching, loss of sync during bootup, running
on the edge of acceptable scan rates, and frequent power cycles, could test
the monitor in ways never dreamed of by the designers.  It may take only one
scan line that is too long to blow the HOT.

  23.17) Vertical foldover

The picture is squashed vertically and a part of it may be flipped over and

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.

  23.18) Comments on vertical problems

(From: Bert Christensen (bert.christensen@rose.com)).

As a general rule, vertical faults can be divided into two types: ones that
cause geometric distortion (a circle will not be round) and those that simply
black out a portion of the screen. The former are faults in the vertical
oscillator, drive, or output stages. The latter are blanking faults. Blanking
faults are almost always caused by electrolytic capacitors changing value and
thereby changing the timing of the pulses which blank the screen during
vertical retrace. In other words, the pulses are turning off the video signals
at the wrong time.

The most common true vertical fault is geometric distortion and a foldover of
white lines at the top of the screen. This is almost always caused by the
electrolytic capacitor on or near the collector of the vertical output
transistor or part of the IC which has the supply voltage (B+) on it. In the
old tube days, the general rule was that bottom distortion was in the cathode
of the output tube and distortion at the top was caused by a fault in the
drive circuit.

  23.19) Excessive width/pincushioning problems

This would mean that the left and right sides of the picture are 'bowed' and
the screen looks something like the diagram below (or the opposite - barrel

However, the obvious symptoms may just be excess width as the curved sides may
be cut off by the CRT bezel.

 \                                          /
  \                                        /
   \                                      /
    \                                    /
     \                                  /
      \                               /
       |                              |
       |                              |
       |                              |
      /                                \
     /                                  \
    /                                    \
   /                                      \
  /                                        \
 /                                          \

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.
For example, if the pincushion correction driver transistor is shorted,
it will have no effect and the picture will be too wide and distorted as
shown above.

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.

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]