Need help for repair of Apple IIgs Monitor!

Need help for repair of Apple IIgs Monitor!

Post by Guido Mock » Tue, 10 Dec 1996 04:00:00



Hi everyone,

the monitor of my old Apple IIgs just died, and I would greatly
appreciate some hints on how to fix it.

The monitor is labelled "Apple Color RGB Monitor". The screen diagonal
is 11" (estimated). It's the one that was usually bundled with an Apple
IIgs.

The symptoms are the following:

For over a year, the monitor occasionally went black, but always came
back to life when given a gentle hit on its right side. Now, it no
longer does.
When I turn it on, I can hear the "degauss procedure" being done. The
normal hiss of the power supply can also be heard. The power LED stays
dark however.

I have already checked as many plugs and cables as possible (also inside
the monitor), but without success. When I turn the brightness to maximum
(using the "screen" control inside the monitor), I can see a horizontal
white line in the middle of the screen. I guess this means that the high
voltage supply and the horizontal deflection unit are still working but
the vertical deflection unit is not. Unfortunately, I have no idea how
to fix it ... it's probably only a minor problem, because for such a
long time, a hit on the side was enough to _temporally_ fix it. But I
have no idea _what_ part is failing.

Any suggestions?

        Guido

 
 
 

Need help for repair of Apple IIgs Monitor!

Post by rubyw.. » Wed, 11 Dec 1996 04:00:00



Quote:Mocken) writes:

>the monitor of my old Apple IIgs just died, and I would greatly
>appreciate some hints on how to fix it.

>The monitor is labelled "Apple Color RGB Monitor". The screen diagonal
>is 11" (estimated). It's the one that was usually bundled with an Apple
>IIgs.

>The symptoms are the following:

>For over a year, the monitor occasionally went black, but always came
>back to life when given a gentle hit on its right side. Now, it no
>longer does.
>When I turn it on, I can hear the "degauss procedure" being done. The
>normal hiss of the power supply can also be heard. The power LED stays
>dark however.

>I have already checked as many plugs and cables as possible (also inside
>the monitor), but without success. When I turn the brightness to maximum
>(using the "screen" control inside the monitor), I can see a horizontal
>white line in the middle of the screen. I guess this means that the high
>voltage supply and the horizontal deflection unit are still working but
>the vertical deflection unit is not. Unfortunately, I have no idea how
>to fix it ... it's probably only a minor problem, because for such a
>long time, a hit on the side was enough to _temporally_ fix it. But I
>have no idea _what_ part is failing.

>Any suggestions?

     Yes. The symptoms you describe fit the infamous Bad HV Module
Connection(s) problem. Most likely, the cure is to resolder all module
contacts. More details, including important safety tips, are below ...

Monitor Repair Mini-Manual  12/96 version

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

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

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.

    * 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 *
   shield built onto the wire. The end of the wire goes to a metal
   clip which, without the * 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 * 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.

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

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).

==========================
<<

     Okay; here is the part which, specifically,
addresses the symptoms you mention ...

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.
<<

     Our GS monitor had the same problem (plus some others-- it has been a
great 'learning laboratory'!).  The cure was discovered by nudging the HV
module with a plastic rod (monitor ON with the case off) and noticing that
the display flicked between collapse and okay.

     Later, continuity tests (with everything OFF and discharged) showed
that some of the HV module's pins were loose, although surrounded by
solder.

    The cause of the problem is having circuit board holes which are too
large for the HV module pins. With standard automated soldering, you end
up with too much of a solder bridge. Eventually, the solder fractures and
all sorts of symptoms crop up. Hand re-soldering of each HV module contact
with good quality solder fixes the problem.

Rubywand

 
 
 

Need help for repair of Apple IIgs Monitor!

Post by Guido Mock » Sat, 14 Dec 1996 04:00:00



>     The cure is to resolder all of the pins coming from the HV module

Yippeah! That was the cure, indeed! Now it's working again.

Thank you very, very, very, very, very, very, very, very, very much!

        Guido

--
Guido Mocken             ** "In nur vier Zeilen was zu sagen,


physik.uni-kl.de for PGP **  die meisten "signatures" brauchen mehr!"

 
 
 

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