GS Monitor Repair (was GS monitor about to give up ghost)

[rubywand@swbell.net]

pubpc1@library.ucla.edu writes ...

> .... it was a horizontal line.  That was a couple of days ago,
> now the screen sometimes splits into two, with the bottom half
> a mirror image of the top.  I may just try to find an Amiga
> VGA to 15kHz analog scan rate converter box and dig up a VGA
> monitor for the GS if all else fails.  :(
> 
> -Scott G.


     Email bounced; so, I'll re-post the Monitor MM. The info below may 
help you fix your monitor's problems.
__________________________________
 

Monitor Repair Mini-Manual  2/97 version

Rubywand to A2-WUG,1wsw, GS.WorldView


 (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.)


Safety

    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, 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.

==========================

Soldering

    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 children.)

==========================

Identity of flyback transistor in Applecolor monitor

From: "John F. Reeves" and Sam Goldwasser

     A user asked about the identity of  ...

"the smoked flyback transistor in my Applecolor monitor. The part bears no 
manufacturer's mark, just two lines of text:

 D1650
    7A

.... The transistor is part Q502 on the PCB of the Applecolor RGB monitor, 
manufactured in 1987. This is the only power transistor in the HV section, 
the only one which is on a heat sink. ...."

D1650 is a 2SD1650 which crosses to an ECG2331. You should be able to
pick one up at your local electronics shop. Try MCM Electronics, Dalbani, 
etc.


==========================

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 small.

    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 sharpness. 

=========================

R/\/\/