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| Lisa 2/10 Video Issue - Vertical Linearity Issue |
Posted by: Zhinü on 2024-04-11 17:26:17
I’m having a weird vertical linearity issue with my Lisa after replacing the potentiometers in both the PSU (the brightness and focus) and also the video board 5 pots. The tube has also been swapped but switching back to original does not fix it.
No amount of adjusting the vertical linearity seems to bring it back, only collapse it into a line if I go too far. I’ve noticed that I accidentally put a 200kohm potentiometer for the height (when the original was 100kohm), but the schematics say to put a 200kohm. Prior to replacing the potentiometers, the linearity was mostly fine. I don’t have the originals unfortunately anymore.
Would anyone have any ideas on what could be happening? |
Posted by: Callan on 2024-04-11 17:33:30
I'm not a lisa expert, but that looks like you have bad caps on your monitor chassis. Your probably gonna have to cap the monitor. That or go through the chassis with an esr meter and see if you can find the bad caps/cap. I'd start in the vertical deflection section. |
Posted by: Zhinü on 2024-04-11 17:48:41
I'm not a lisa expert, but that looks like you have bad caps on your monitor chassis. You’re probably gonna have to cap the monitor. That or go through the chassis with an esr meter and see if you can find the bad caps/cap. I'd start in the vertical deflection section. I was kinda thinking bad caps, but it appeared after I put in new potentiometers. When I first got the Lisa, the linearity was fine. Though, that was a few months back, and I kinda procrastinated on replacing the potentiometers in the PSU AND Video board. |
Posted by: Callan on 2024-04-11 19:38:30
Foldover and vertical compression like that is usually indicative of a cap out of tolerance. It could just be coincidence, but since your problem didn't appear until you replaced the pots I would check their resistence first. Problems always have a funny way of being at the last place we 'fixed' something. |
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