Re: Ack! More IIGS monitor problems!

[Rubywand <rubywand@swbell.net>]

Jon H. wrote:
> 
> Hi folks,
> 
> I posted here a few days ago about my IIGS's monitor having jagged lines
> across the display.  I fixed that (thanks for the help, by the way) but I
> have another problem now.  My monitor has a nice sharp, clear picture, but
> every now and then the picture starts to shimmy.  It gets really annoying
> at times. Is there a way to fix this, or will I be needing a new monitor?
> ....

     This sounds like the same problem cropping up in another form.

     The jagged lines occurred when the monitor failed to lock onto the
Horizontal Sync pulse included in the video signal from the GS. The
lines of video (dot) information were showing up at skewed positions on
the display and wrapping around instead of all starting at the same
place on the extreme left and ending at the extreme right.

     Changing the Horizontal Hold setting let the monitor achieve lock
and the dots 'lined up' the way they are supposed to. Side-to-side
shimmy indicates that Horizontal lock is not entirely stable.

     An obvious fix try is to adjust Horizontal Hold (the "<- ->"
knob/stub) until the shimmy stops. This works fine unless  1- The HH
control is already at its extreme setting,  2- The HH control has
'dirty' or burn spots at the position which would, ordinarily, be the
correct setting,  3- The display stabilizes but ends up moved too far to
the left or right side of the screen.

     Maybe the control is already as far as it will go; or, you get
stability but the display is jammed against the left side with a large
blank space on the right. There is a chance you may be able to get some
extra Horizontal adjustment 'breathing space' by diddling the the other
two controls on the back (Vertical Hold and Vertical Size).  Monitor
controls interact somewhat; so, for example, a change in Vertical Size
can impact Horizontal Hold. 

     Something else to try is removing the monitor cable and cleaning
the plug and sockets with an alcohol swab.

     Beyond the above tries, you are most likely looking at 'biting the
bullet' and removing the case.

     If your HH control seems to abruptly lose/regain/lose lock as it is
turned, there is a good chance that it's 'dirty'. The usual cure is to
remove the case (following safety precautions such as those described
earlier-- unplug monitor, let it sit several hours, Wear Goggles, don't
stress CRT neck, etc.) and squirt some Control Cleaner into the control
(where the wiper touches the resistance element) while working the knob
back and forth.

     Once you go to the trouble of removing the case, be sure to give
all three back controls the Contol Cleaner treatment. Detatch and clean
the controls mounted to the side of the case, too; and, clean the case
thoroughly. 

     With the case removed, you will have access to some other controls
which may help solve the shimmy problem. Two are on the black High
Voltage module: one nub controls base Intensity; the other controls
Focus. There are also a couple small tab switches located near the back
edge of the main circuit board. One sets Horizontal position; the other
sets Vertical position.


     If you reconnect the side controls and power cord, you will be able
to experiment with adjustments.

     Working with monitor adjustments with the case removed requires
constant awareness of potential hazards. For example, you would connect
the AC power cord to the monitor _before_ plugging it into an AC socket.
The monitor needs to be on a plastic or wooden table with nearby clutter
removed. It may be easiest to support with the rear of the circuit board
resting on a thick magazine.

     You should have one or two plastic TV technician tools. These are
rods with ends for turning slotted controls.  (A whole set will cost a
few dollars at Radio Shack.)  Such tools are handy for adjusting the
controls on the back of the HV module, for flipping the tab switches,
for tapping components you suspect may be loose, etc.. 

     Avoid using long metal screwdrivers anywhere near the monitor; it
is too easy to catch an arc from a high voltage area or to bump against
something and get zapped. (By the way, getting zapped is seldom fatal in
itself. The usual shock hazards come from your response to the shock--
like slamming into the monitor, breaking the CRT, falling off your
stool, smashing through a window, etc..)  Naturally, if you leave the
exposed monitor work area, you need to be concerned about anyone who
might walk by and touch something.

     After connecting the monitor to the GS, arrange things so that all
controls are accessible and turn ON the monitor and GS. Get a Finder
display with an open folder listing files. This is a good general
purpose display for making monitor adjustments. Let the monitor warm up.

     The first thing to check for is a loose HV module. Using a plastic
rod, tap the black HV module. If nothing much happens, fine. If the
display jumps, flattens, or otherwise bombs, you probably have one or
more fractured solder connections where the module connects to the
circuit board. The cure is to turn everything OFF, pull the power cord,
let the monitor sit several hours, and re-solder the HV module
connections-- they are in a group on the bottom side of the board.
Although there is certain to be a high voltage charge on some of the
pins, the soldering need not be especially hazardous. The only things
touching the board or any part of the monitor are the solder (held by
one hand) and the tip of an insulated-handle soldering iron. (Never
touch two different electrically-conductive parts of a monitor at once.)

     The two in-case controls most likely to be helpful in correcting a
Horizontal problem are the Horizontal tab switch and the Intensity
control. (I don't remember exactly which tab switch sets Horizontal
position or which of the controls on the HV module is Intensity. You can
experiment and easily discover this for yourself.)

     Working with Horizontal Hold, the Horizontal tab switch, and the
Intensity control on the HV module, (and, maybe, the Focus control and
Vertical Size) you should be able to eliminate any shimmy and end up
with a properly sized and positioned display.

Note: On some monitors, you may have to trade-off Vertical Size in order
to get a stable display which retains good linearity. 

     Once the shimmy problem is cured and the display is the right size
and positioned correctly, work back and forth between the side controls
and Focus to get a sharp display. What you want is good brightness and
sharpness with the side controls near their middle positions. 


> PS - I doubt that there's any kind of interference between the monitor and
> other electrical devices, because I have been moving the IIGS all around my
> room, and the results have been the same.

     Right; interference does not, generally, cause shimmy. If your AC
power is subject to glitches and brief voltage drops, one result could
be shimmy. However, if you notice no drop in intensity or change in
size, whatever dips you're getting should not cause shimmy unless your
Horizontal Hold setting is borderline -- i.e. it is just on the edge of
losing sync (in which case the steps outlined above would be in order).

     If you have pretty 'dirty' AC power, it can cause all sorts of
problems. An Uninterruptible Power Supply will provide de-glitching,
stabilize voltage supplied to your monitor and computer, and guard
against data loss/ hard disk crashing should AC line power suddenly
cease during a disk write. At around $120, a UPS is one of the best
investments a computer user can make.

     One form of interference which used to plague microcomputer
experimenters is AC hum. Our "TV Typewriter" and other home-brew monitor
setups sometimes picked up 60-cycle hum which usually showed as an
up-down sliding area of brightness or swelling. Sometimes, the
horizontal would be affected and we'ed get wavy edges on each side.
Unless a GS monitor cable develops a break in a ground or shield lead,
such interference should not be a problem on the GS monitor.
  


Rubywand