Monitor Repair Mini-Manual

by Jeff Hurlburt

(This mostly came from COMPUTIST articles. There have been some valuable
contributions by csa2 readers, too.)

Mainly, this mini-manual relates to fixes which involve removing the case. Before
removing the case, check to see that the your problems are not due to a poorly
connected monitor cable.

Also, try diddling the side and back controls. Sometimes, these become dirty or
develop bad spots. If diddling a control cures an unstable, jumping, etc.
display, you can be fairly sure that a squirt of Control Cleaner will help. (You
will still need to remove the case; but, at least, you will know what to do.)


Basically: unplug the monitor and let sit for a day, wear goggles, work on a
non-conductive table surface, do not stress CRT neck.

Unplugging the monitor and letting it sit for a few hours reduces the danger of
shock from stored charges; it does not eliminate it. The usual warning for this
kind of work is AVOID touching two different circuit points at the same time.
Like, don't touch the metal chassis and the conductive surface of the CRT at the
same time.

WEAR protective GOGGLES. If you should, somehow, bump or stress the CRT neck-- as
in jumping when you get shocked-- it may break. The result may be a peaceful
THOOP! or the CRT may implode in a spray of glass. (Avoid using the CRT's neck to
support the monitor in any position.)

Work on a wooden or plastic-topped table with plenty of space. Try to position
yourself, tools, and the monitor so that when you get 'stung', the chances of
breaking something are reduced.

As much as posible, avoid using heavy tools of any kind. An inadvertant tap from
a mini-screwdriver is much less likely to crack the CRT than a bonk from a
full-sized screwdriver or pair of pliers.

Rubber gloves are probably a good idea so long as they do not get in the way. Of
course, pointy connections and components can puncture gloves.

It's a good idea to clip a wire to the chassis and touch the other end to the
conductive surface of the CRT a few times before doing any work in order to drain
off any charge there.

Note: Several places in a monitor or TV carry high enough voltages to deliver an
uncomfortable shock. Draining the charge from one point does not guarantee that
other points have been discharged.

Joe Walters contributed some info on Discharging the HV anode ...

The HV charge (20,000+ volts) might not be much reduced by just waiting a few
hours (or days), especially if you are in a low humidity location and the tube,
etc., are all of good quality.

1. There is a long wire (called the anode) that goes from the high
voltage power supply to the top of the tube where it is snapped into a hole. You
can't see the hole because there is a rubber shield built onto the wire. The end
of the wire goes to a metal clip which, without the rubber shield, looks somewhat
as below. One squeezes the clip so the end slips into the hole in the tube.

--- ---
== \ / ===== back of CRT
\ / <-- metal clip (This is what your grounded
| screwdriver needs to touch.)
[|] insulated Anode lead going to HV module [|]

Needless to say, UNPLUG the monitor before beginning. Simply turning it off isn't
good enough.

2. Get a clip lead and clip one end to a long slender screwdriver

3. Clip the other end to the metal chassis of the TV (i.e the metal frame parts)

4. Carefully! slip the screwdriver tip under the rubber flap on the
top of the tube until it touches the internal wire that both holds the anode wire
in place and conducts electricity.

Step 4 may result in a somewhat loud "SNAP" as the tube is discharged. Be
prepared so you don't jump and break something.


Opening the Case ...

Whatever it is you plan to fix, if you remove the monitor case, you will probably
need to unplug the cable running from the circuit board to the Controls/Switch
Module on the side of the case. Use 'whiteout', nail polish, etc. to mark the
position of the plug. In more detail ...

1. Unplug everything from the monitor & let it sit for a day.

2. Put on protective GOGGLES. Place the unit face down on a wooden or
plastic-topped surface with lots of space and good lighting. Remove the the
screws. Place the unit in nomal position.

3. Have a fat magazine ready. Slide the case off until you are able to see the
control leads plugged into the main board on the right side of the case. Mark the
plug position with 'white-out', nail polish, etc.. Unplug the connector.

4. Slide off the case while supporting the monitor and slide the fat magazine
under the circuit board to prop up the monitor from behind.

5. Discharge the HV (optional, but, generally, but a good idea).

6. <Do adjustments, fixes on Monitor>

7. When done, reinstall the control assembly.

8. Still wearing GOGGLES, support the monitor, remove the magazine, slide on the
case, reconnect the plug, finish sliding on the case, replace screws.



For any soldering use a good quality pencil-style iron rated at 25-40 watts with
a holder. Use high quality (60/40 or better) rosin core solder (e.g. Kester "44"
20 gauge).


Flickering, Jumping, ...

If the monitor exhibits major flickering, periodic collapse of the display to a
line, etc., then it may help to know that a common source of such problems is one
or more bad connections where the High Voltage module is joined to the main
circuit board. (This module is the black thing with a HV lead running to the
CRT-- it's near the left, back. The slotted nub controls in its case set Focus
and base Intensity.) Often these connections look okay because it is hard to see
the small fractures in the solder surrounding the pins.

The cure is to resolder all of the pins coming from the module (on the under-side
of the circuit board). Before doing the soldering, clip a wire to the metal
chassis and touch the other end to each HV module pin and other points in the
area. While soldering, avoid touching anything conductive on the monitor with
anything but the iron and solder.


All-blue, all-red, etc. screen?

You probably have a blown choke on the little chroma board mounted to the back of
the CRT. The choke will be connected to one of the larger, R/G/B output
transistors. Use an Ohmmeter to find the open choke. Replace the bad choke with
'one like it' or brew your own: wind about 25-30 turns of #30 wire on a small
ferrite core.

A more detailed procedure is presented below ....

1. The part that causes the problem when it fails is a "choke" or "inductor" , it
is mounted on a small circuit board attached to the back of the monitor tube
itself. This part looks like a small blue ceramic ball with two leads coming out
the bottom, and is color coded for 10 microhenries.

2. There are three of these items on that circuit board, and if any one of them
fails, the symptom is a screen all of one color, with total loss of any controls
of the monitor. The parts are identified by number, and what color the screen is
will tell you which one to replace.

L6R2 for a Red screen
L6G2 for a Green screen
L6B2 for a Blue screen

3. You can probably get a 10 microhenry choke at Radio Shack, or it is available
for $1.28 (plus a $5 Handling charge) from Digikey Corporation
at (800) 344-4539. They take Mastercard, Visa, and C.O.D.

The Digikey part number is M8025-ND.

4. After replacing this part, the monitor colors may need to be readjusted via
the small color trimpots on the same circuit board.


RGB Adjustments Info

This is what some of the RGB pots are:

R13 RGB Intensity
C86 Horizontal Position on RGB
C85 NTSC Color Hue Adjustment
C45 NTSC Frequency Adjustment


Centering Adjustments (from James Poore)

Color monitors do vertical and horzontal centering differently than do monochrome
monitors. Almost all color monitors have either a jumper arrangement or actual
centering controls, sometimes both. Centering adjustments are usually located on
the PCB with no access holes, so the back will most likely have to be removed to
get to them.

If your monitor uses jumpers, there should be 3 tabs that each jumper can
be connected to. For vertical adjustment the tabs should be marked as 'up',
'down', and center. If your pix is too high, then you would connect the jumper to
the down tab. For horizontal adjustment the three tabs should be marked 'left',
'center', and 'right'.

If your monitor has centering controls, then adjust for best centering.

Many GS monitors use small tab switches to adjust centering. These are located
near the back of the main circuit board. ______________

Adjustment of Vertical Size, etc. via shafts on back of GS monitor can affect
centering. For small changes, these adjustments may get the job done.

Adjustment of Intensity and Focus (see below) can affect centering.


Adjusting Focus and Intensity on a blurry GS RGB Monitor.

These adjustments may also help cure display "bowing", etc..

Intensity and Focus controls are on the High Votage Module (black module near
back of circuit board) inside the case.

Follow procedure outlined earlier for safety (e.g. unplug, wait, wear goggles,
...) and removing the case.

Note the position of the two controls on the HV Module (at the left, back). Mark
the back of the cover where handy access hole should be.

Take the case cover to another area (i.e. away from the exposed CRT neck).

Remove the control assembly from the right side of the case.

Using a Dremel tool, hole saw, ... cut an approx. 1" diameter hole in the back of
the case. Use this opportunity to give the case interior a good cleaning. (If you
wash it, be very sure it's dry before continuing.)

Reinstall the control assembly.

Put everything back.

Reconnect cable and AC cord. Turn on the computer & monitor. Let it sit 10-20
minutes. Use the normal side of case controls to get the brightest,
'decent-focus' picture you can obtain.

Using a plastic TV technician's tool (and flashlight if necessary) adjust the
Intensity and Focus controls (through the hole in back on the HV module) to get a
good looking display.

Work back and forth between the back and side controls. What you're aiming for is
a display with good brightness and sharp focus when the side controls are near
their middle positions.

Cover the back hole using a piece of duct tape, a large sticker, etc.. (The
opening is a potential shock hazard, especially if the monitor is within reach of


Shrinking, Flicking in-out of Focus, ...

Arcing from the metal brace to the HV module can cause the display to momentarily
shrink and flick out of focus.

Follow safety and setup procedures outlined earlier.

The cure is to bend the brace up enough to increase the arc path and clean the
surfaces involved. Apply HV dope to the brace and module where distances are

If the case interior seems pretty clogged with dust and gunk, it's a good idea to
remove the side-mounted Controls/Switch Module and give the case a good washing.
(Be very sure it is well dried before replacing.) You should also clean the two
controls on the C/S Module with spray-in Control Cleaner.

Before putting the case back, this may be a good time to adjust base Intensity
and Focus (the two nub controls on the HV module). Position the monitor so that
screen is easy to see and the nub controls are accessible. Plug in the the C/S
Module. Adjust the C/S Module controls to center positions. Plug in the monitor
to the computer. Get a Desktop display with some text and icons. Use an insulated
tool to adjust the nub Intensity and Focus controls for maximum sharpness at
'normal' viewing intensity. A magnifying glass is helpful to obtain max pixel

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