Notes on the Troubleshooting and Repair of Computer and Video Monitors


  9.21) 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.

  9.22) 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.  To locate the vertical output circuitry without
a service manual, trace back from the deflection yoke connector.  The vertical
coils will be the ones with the higher resistance if they are not marked.

  9.23) 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.

Another 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.

If your AC power fluctuates, an inexpensive monitor may not be well enough
regulated and may pass the fluctuations on as jitter.  The video card is
unlikely to be the cause of this jitter unless it correlates with computer
(software) activity.

  9.24) 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 monitor 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 monitor 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.

  9.25) Horizontal output transistors blowing at random intervals

The HOT may last a few minutes, days, 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.

  9.26) 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.

  9.27) 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.

  9.28) Uncorrectable pincushion distortion with new monitor

"I just bought a new Sony 200SX 17" monitor and I just can't get the
 pin-cushion control to work right. If I get the outer edges straight
 then any window an inch or so from the edge will curve like crazy. The
 only way around this is to shrink my screen size so I'll have 3/4 in or
 so of black space. This is very irritating since I am not getting the
 15.9" viewable size as advertised. Is this normal?"

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

The distortion that you describe is called 'inside pincushion'.  Normally it
can be corrected by a dynamic S-correction circuit.  Maybe Sony didn't do a
too good job on this, or none at all.  It may also be that the correction is
optimized for certain horizontal scan frequencies only, as dynamic S-correction
is a resonant circuit. You might want to test at another frequency.

(From: markmtf@earthlink.net)).

You may have a monitor that is at the edge of the acceptance tolerance, (which
is a defined acceptable variation for cost and production yield reasons). A
typical worse case tolerance may be up to 3mm of a deviation from a straight
line for the edges. This applies for all monitors and all manufacturers. Of
course some companies actually control the variation better than others, (and
some just say they do).

For reference; try using the "Recall" function which will set the adjustments
to the original factory settings. (This assumes that your video timing matches
the preset timing used in the factory). Check the infamous user manual.

  9.29) Deflection yoke testing

A faulty deflection yoke can affect the geometry (size and shape) of the
raster, result in insufficient high voltage and/or other auxiliary power
problems, and blow various components in the low voltage power supply or

* A simple test to determine if the yoke is at fault for a major geometry
  problem (e.g., a keystone shaped picture) is to interchange the connections
  to the yoke for the axis that is not affected (i.e., the vertical coils if
  the width is varying from top to bottom).  If the raster/picture flips
  (indicating that you swapped the proper connections) but the shape of the
  raster remains the same - the geometry is unchanged, the problem is almost
  certainly in the deflection yoke.

* Where high voltage (and other flyback derived voltages) are reduced and
  other problems have been ruled out, unplugging the deflection yoke (assuming
  no interlock) may reveal whether it is likely at fault.  If this results in
  high voltage and a relatively clean deflection waveform or returns the power
  supply or deflection chip load to something reasonable, a defective yoke is
  quite possible.

  CAUTION: powering a TV or monitor with a disconnected yoke must be done with
  care for several reasons:

  - The CRT electron beam(s) will not be deflected.  If it turns out that the
    yoke is the problem, this may result in a very bright spot in the center
    of the screen (which will turn into a very dark permanent spot quite
    quickly) :-(.  Disconnecting only the winding that is suspect is better.
    Then, the other direction will still scan resulting in a very bright line
    instead of a super bright spot.  In any case, make sure the brightness is
    turned all the way down (using the screen/G2 control on the flyback if
    necessary).  Keep an eye on the front of the screen ready to kill power at
    the first sign of a spot or line.  Disconnecting the CRT heater as an
    added precaution would be even better unless you need to determine if
    there is a beam.

  - Removing the yoke (which is effectively in parallel with the flyback)
    increases the inductance and the peak flyback voltage on the HOT.  In the
    extreme, this may blow the HOT if run at full line voltage/normal B+.  It
    is better to perform these tests using a Variac at reduced line voltage if

  - The deflection system will be detuned since the yoke inductance plays a
    very significant role in setting the resonance point in most designs.
    Don't expect to see totally normal behavior with respect to high voltage.
    However, it should be much better than with the faulty yoke.

* If possible, compare all measurements with a known good identical deflection
  yoke.  Of course, if you have one, swapping is the fastest surest test of
  all!  In many cases, even a not quite identical yoke will be close enough to
  provide useful information for testing.  However, it must be from a similar
  piece of equipment with similar specifications - size and scan range.  Don't
  expect a color TV yoke to work in a high performance SVGA monitor!

  Note: the substitute yoke doesn't have to be mounted on the CRT which would
  disturb purity and convergence adjustments but see the caution above about
  drilling holes in the CRT face plate!

The deflection yoke consists of the horizontal coils and vertical coils (wound
on a ferrite core), and mounting structure.  Little magnets or rubber/ferrite
strips may be glued in strategic locations.  DO NOT disturb them!  In rare
instances, there may be additional coils or other components mounted on the
same assembly.  The following deals only with the actual deflection coils
themselves - the other components (if any) can be tested in a similar manner.

Where the test procedure below requires removal of the yoke, see the section:
"Removing and replacing the deflection yoke" first.

* Horizontal - the horizontal section consists of an even number of windings
  hooked up in parallel/interleaved with half of the windings on each of the
  two ferrite core pieces.

  The horizontal windings will be oriented with the coil's axis vertical and
  mounted on the inside of the yoke (against the CRT neck/funnel).  It may be
  wound with thicker wire than that used for the vertical windings.

  - Resistance check - This may be possible without removing the yoke from
    the CRT if the terminal block is accessible.  Disconnect the individual
    windings from each another and determine if the resistances are nearly
    equal.  Check for shorts between windings and between the horizontal and
    vertical windings as well.

    Typical resistance of the intact windings (at the yoke connector assuming
    no other components): TV or NTSC/PAL monitor - a few ohms (3 ohms typical),
    SVGA monitor - less than an ohm (.5 ohms typical).

  - Inspection - Look for charring or other evidence of insulation breakdown
    due to arcing or overheating.  For the horizontal windings, this will
    require removing the yoke from the CRT since little if any of the windings
    are visible from the outside.  However, even then, most of the windings
    are hidden under layers of wire or behind the ferrite core.

  - Ring test.  See the document "Testing of flyback (LOPT) transformers".
    This deals with flyback transformers but the principles are the same.
    Disconnecting the windings may help isolate the location of a fault.
    However, for windings wound on the same core, the inductive coupling
    will result in a short anywhere on that core reducing the Q.

* Vertical - The vertical section is usually manufactured as a pair of windings
  wired in parallel (or maybe in series) though for high vertical scan rate
  monitors, multiple parallel/interleaved windings are also possible.

  The vertical windings will be oriented with the coil's axis horizontal and
  wound on the outside of the yoke.  The wire used for the vertical winding
  may be thinner than that used for the horizontal windings.

  - Resistance check - This may be possible without removing the yoke from
    the CRT if the terminal block is accessible.  Disconnect the individual
    windings from each other and determine if the resistances are nearly
    equal.  Check for shorts between windings and between the horizontal
    and vertical windings as well.

    Typical resistance of the intact windings (at the yoke connector assuming
    no other components): TV or NTSC/PAL monitor - more than 10 ohms (15 ohms
    typical), SVGA monitor - at least a few ohms (5 ohms typical).

  - Inspection - Look for charring or other evidence of insulation breakdown
    due to arcing or overheating.  The accessible portions of the vertical
    windings are mostly visible without removing the yoke from the CRT.
    However, most of the windings are hidden under layers of wire or behind
    the ferrite core.

  - Ring test - Since the vertical windings have significant resistance and
    very low Q, a ring test may be of limited value.

  9.30) Deflection yoke repair

So you found a big black charred area in/on one of the yoke windings.  What
can be done?  Is it possible to repair it?  What about using it for testing
to confirm that there are no other problems before ordering a new yoke?

If the damage is minor - only a few wires are involved, it may be possible to
separate them from each other and the rest of the winding, thoroughly clean
the area, and then insulate the wires with high temperature varnish.  Then,
check the resistances of each of the parallel/interleaved windings to make
sure that you caught all the damage.

Simple plastic electrical tape can probably be used for as insulation for
testing purposes - it has worked for me - but would not likely survive very
long as a permanent repair due to the possible high temperatures involved.
A new yoke will almost certainly be needed.

  9.31) Testing of flyback (LOPT) transformers

How and why do flyback transformers fail?

Flybacks fail in several ways:

1. 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).

2. 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.

3. 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.

4. Internal short circuits in the windings.

5. 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.

  9.32) Picture size suddenly becomes larger (or smaller)

You are playing your favorite game (read: addiction) and suddenly, the
picture size increases by 20% and the brightness may have changed as
well.  What part should I replace?  I only used my phasers on the #3

Unfortunately, I do not have a crystal ball.  There are a number of parts
that could be faulty and no way of know for your monitor and your symptoms
which it is.  Sorry, you will almost certainly have to have it professionally
repaired or replaced.

What it sounds like is happening is that the circuitry that selects internal
components depending on scan rate have failed in some way.  They could be
making an incorrect selection or the power supply could be faulty and applying
an incorrect voltage to the horizontal and vertical deflection circuits.  The
brightness changes since it is not compensated for properly.

  9.33) Burning up of various size or centering resistors

Check the capacitors that couple the yoke to to ground.  If they become
reduced in value or develop a high ESR, the current will be diverted to other
components with unfortunate and rapid consequences.

  9.34) Picture shifted horizontally

The first thing to determine is if this is a position or phase problem:

* A fault with horizontal position means that the entire raster is shifted
  left or right.  This is almost certainly a monitor problem.  If you turn
  up the brightness control, the edges of the scan lines will probably be
  visible on one side.

  - Assuming the position or centering controls do not work at or or have
    insufficient range, check for a defective centering pot and bad centering
    diodes and other components in their vicinity.  If digitally controlled,
    you will probably need a schematic to find the cause.

  - If the monitor was dropped, the yoke or other assembly on the CRT neck
    may have shifted (though there would probably be other symptoms as well).

  - Monochrome monitors have centering rings on the CRT neck which may have
    be knocked out of adjustment.  Color monitors adjust the centering
    electronically since magnetic rings would mess up the purity and/or

* A fault with horizontal phase means that the raster is still centered on
  the screen but the picture itself is shifted (and may have some wrap-around)
  within the raster.  This could be a fault in the monitor or video card or
  incorrect settings in the software setup for the video card.

  - If this happened while trying out this monitor on a different or modified
    computer, just after you have done a software upgrade, or just after
    something strange happened (like your PC's CMOS settings got corrupted -
    monitor settings are generally not in the CMOS setup but may have been
    affected at the same time), reset the monitor's controls to their default
    or middle position and then use the software setup or install program that
    came with your video card to set scan rates, size, position, and sync

  - Some monitors have a user accessible horizontal phase control in addition
    to horizontal position.  This adjusts the delay in the sync circuits so
    check that area of the electronics if the control doesn't work or have
    enough range.

* There could also be a problem with base drive to the HOT.  This may result
  in position, phase, size, and linearity errors as the scan being initiated
  too soon or too late.

  - Weak drive to the HOT due to faulty components in the base circuit or
    driver stage might result in the HOT coming out of saturation early.  The
    picture would be shifted to the right and the HOT might run excessively
    hot and blow.

    WARNING: The case of the HOT has >1,000 V spikes and B+ when off - don't
    touch with power on or until you confirm no voltage is present after
    pulling plug.

  - If marginal, a drift of position, phase, size, and linearity with warmup
    is also likely.  Check for dried up electrolytic capacitors and use cold
    spray to isolate other bad components.  If the drive becomes too weak,
    the HOT may blow after after being on for a while.

Chapter 10) High Voltage Power Supply Problems

  10.1) HV power supply fundamentals

Most, monitors derive the high voltage for the CRT second anode (THE high
voltage, 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.
Of course, if the vertical deflection dies....

Some high end monitors utilize a separate high voltage supply.  One reason
for this approach is to decouple the horizontal deflection from the HV
in auto-scan monitors thus simplifying the design.

Usually it is a self contained inverter module.  It if can be opened, then
repair may be possible.  With a separate HV supply, there is no need for a
HV flyback transformer on the mainboard.  Some designs may use a separate HV
supply including a flyback which is part of the mainboard but is self
contained and independent of the horizontal deflection system.

Most TV and monitor (flyback) high voltage supplies operate as follows:

1. 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 than transformer as far as the primary drive is concerned.

2. 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

3. 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.

4, The capacitance of the CRT envelope provides the needed filtering to
   adequately smooth the HV pulses into a DC voltage.  Sometimes there is
   a separate HV capacitor as well.

5, 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.
   The focus and screen are generally the top and bottom knobs, respectively.
   Sometimes they are mounted separately.  This or a similar divider may
   also provide feedback to control high voltage regulation.

  10.2) What is a tripler?

In some TVs and monitors, 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 and monitors 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 monitor 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?  For example, has it suddenly gotten brighter
than normal or has the size decreased? 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).

If the horizontal frequency is not correct (probably low) due to a faulty
horizontal oscillator or sync circuit or bad horizontal hold control (should
one exist!), HV may increase and trigger shutdown.  Of course, the picture
won't be worth much either!  With a multiscan monitor, this could happen if the
mode switching is faulty resulting in incorrect component settings for a
given scan rate.  A symptom might be HV shutdown when switching into scan

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.
See the section: "Apple/Sony monitor dies after variable length of time".

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