16.014 Suddenly my GS monitor exhibits a serious case of display shimmy which sometimes degenerates into jagged lines. How can I fix this problem?
Description
This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
16.014 Suddenly my GS monitor exhibits a serious case of display shimmy which sometimes degenerates into jagged lines. How can I fix this problem?
Side-to-side shimmy indicates that Horizontal lock is not stable.
A good fix try is to adjust Horizontal Hold (the "<- ->" knob/stub) until
the shimmy stops. This usually works 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.
If, adjusting Horizontal Hold does not fix the problem, you will probably
need to remove the case. For starters, this will let you squirt some Control
Cleaner into the HH control.
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..
Note: If the HH control seems to have serious burn spots-- e.g. you notice a
crunchy feel when turning the knob-- you may have to get it replaced in order
to achieve a correct setting. Replacing such a control is a job for someone
with experience in working with monitors or TV's. If you decide to do it, be
sure to check safety and setup suggestions listed earlier. De-solder the
control, remove it, and take it to an electronics parts seller to get a
replacement.
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.
======= End of Monitor Repair Mini-Manual =========
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