Display issues

My other posts this evening talk about replacing electrolytic capacitors, particularly the power supply. My motivations for looking into this are basically (a) suspicions about my elderly capacitors just nearing the end of their lives, (b) trying to revive an old power supply that I have, and (c) some video problems I’ve seen on both of my Lisas. Although I suspect that at least one of these problems may be due to the power supply, I thought I should ask the much more knowledgeable people here and be certain.

On the Lisa 1: the display looks bright and crisp, with little evidence of waviness whatsoever. There is some very minor distortion: scanlines at the top of the screen are more widely spaced than those at the bottom (Example: https://goo.gl/photos/C4Cc7tecNMt5fRXv7). I can live with that, though.

The main problem is that the screen brightness occasionally goes haywire. It doesn’t flicker—instead, at random intervals, the brightness will ramp down smoothly, as if someone triggered the “privacy screen dimming” feature. Sometimes it won’t ramp down completely—it’ll just go partway. Other times, though, it smoothly fades to black, and then after just a second or two, it will POP back to full brightness.

Meanwhile…

On the Lisa 2: first of all, the screen is pretty dim and takes a while to “warm up”. When it does, the edges of the display and vertical lines have a very slight waviness to them. This waviness varies horizontally no more than a quarter millimeter, let’s say, and vertically the “period” is maybe 3mm or 4mm. The waviness will “roll” up the screen and will gradually go away the longer the Lisa is running.

I’ve also observed occasional positional flickering, where the picture will displace itself horizontally very briefly—barely a flash—before snapping back into place. (May be a video board issue here?)

Any ideas what could be causing these things?

Thanks,

—Tom

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