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3.16.1. My Lisa's video display is unstable, how do I fix it?

My Lisa seems to be having a problem with its video. When I power it up, it boots properly but the video jumps a lot. For example, the vertical height of the image may jump between normal size and very narrow with a large black border, or the video will roll like an old TV with the vertical hold misadjusted. When I first got the Lisa everything was fine but it's been moved around some and I think it might've jostled the video adjustments.

Original source of question: Clinton Yelvington / LisaList 2005.05.26



Try some contact cleaner on the pots at the top of the video board. HAVE THE SYSTEM OFF AND UNPLUGGED over night. High voltage danger!

First use a marker to mark where they are set.

Spray the pots with the contact cleaner then adjust them back and forth. Because you marked where they were set, you can put them back.

Answer Source: Jason Perkins / LisaList 2005.05.27


If the monitor's height jumps flickering, it possible will be a dirty pot on the video board. If I remember right it must be one of the two in the center of the six pots top on the board or the right one. Just try to adjust the a little and see, what happens. But beware of high voltage near the tube !! Or check the correct connection of the plug from the board to the tube deflection unit (sometimes the plugs connection to the board is faulty too)


if the height slides slowly from min. to max. and back again, then this could be wrong. Take a look at a vertical mounted coil in the center of the video board. I have seen several Lisas with overheated coils for deflection. Some of them were no more coils they have been a chaotic ball of wire, because the coils core has melted. But the Lisas still worked :-) Or check the perhaps afterwards mounted second coil (glued on the right vertical metal housing near the tube, which is connected serial between the two plugs of the board and the tube deflection unit. But I think you don't have such an additional coil, because you wrote you have a non modified Lisa 2...

Source: macmoni (Tom from Bavaria) / LisaList 2005.05.27


If the potentiometers are still sensitive after cleaning, they may need to be replaced. Suitable replacements are still available (ca. 2006). eg. Bourns 3352T series, available from DigiKey as part numbers:

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