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From: rubywand@aol.com (RUBYWAND)
Newsgroups: comp.sys.apple2
Subject: Re: Repair Apple IIGS RGB, info wanted
Date: 21 Mar 1996 14:56:34 -0500
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Monitor Repair Mini-Manual (mostly from stuff in COMPUTIST)
First, be safe. (See safety stuff at end.) Mainly, unplug the monitor
and let sit for a day, wear goggles, work on non-conductive table surface,
do not stress CRT neck.
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.
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.
For all 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).
Arcing from the metal brace to the HV module can cause the display to
momentarily shrink and flick out of focus. 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 is 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.
_____
Safety
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. 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.
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.
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.
Rubywand