Apple //c "Doing the wave"

[jlevenso@Rosie.UH.EDU (jonathan levenson)]

I have a "Unidisk" //c (ie, no ram expander connector, but can
accept unidisk drives, fast modems)

I have connected two different NTSC type monochrome monitors
to the composite output port on the //c and get strange "waving"
behavior.  Specifically, about 15 scanlines at a time gradually
shift approx 15-20 pixels to the left, then they realign to center.
The problem is usually minor upon powerup, but gradually worsens
as the computer heats up.  I've taken a brief look "under the
hood" and have found no obvious problems, aside from some dust.
I have removed as much of the dust as possible, and also reseated
all of the socketed chips.  Still, the problem persists.

Is this a common //c problem that can be solved relatively easily?
Could I fix it by swapping out a logic board of some kind?
Or is it just easier to go buy a new //c?
(I would like to get this one working however..)

Thanks for help in advance,
JML


Note: I have connected the same monitors to my //GS composite out
and do not get the "waving" behavior, so I'm pretty convinced
it's the //c.