General Category > LisaList2
Apple Lisa Scrolling and Jumpy Display
AlexTheCat123:
I bought a Lisa late last year and got it fixed up with the help of the members of this community (see the topic "Does anyone have a spare Lisa motherboard?" for details), but it has unfortunetely started having problems again. The image on the CRT started scrolling a few months ago, but it was still somewhat usable because the scrolling was so slow. A few days ago, however, the problem got worse. Now the picture's vertical height is very jumpy and it randomly changes height while the Lisa is running.
Most of the time, there is only a single horizontal line on the display, but it will occasionally enlarge for a few seconds before returning to the horizontal line again. You can see the scrolling issue and some slight vertical jumping (although not nearly as bad as it is now) at about 4:58 in this YouTube video that I made about the computer: https://www.youtube.com/watch?v=6hStH5EwmfY. Do you have any ideas about what may be causing this issue? I have already tried playing with the potentiometers on the video board and they don't seem to be helping at all.
stepleton:
It seems likely that there is a fault on the video board. I suppose this is obvious...
I don't know the answer here, but for problems like these, you may benefit from reviewing the video diagnostics advice for compact Macs in The Dead Mac Scrolls. This book isn't about the Lisa, but generally the parts and problems that it talks about have direct analogues on Lisa video boards. You may need to look at schematics to identify which Lisa components are the same as the Mac ones, but since the book calls out specific components and explains what the components do, it may not require too much detective work.
rayarachelian:
So that sounds like the vertical hold pot on the power supply, gently wiggle that guy while the Lisa is off it might help clean it. If not it might be some other thing on the analog video board behind the CRT such as the two trimpots in the FAQ answer or the coil in the middle.
see:
* https://lisafaq.sunder.net/single.html#lisafaq-hw-vid_jumpy
* https://lisalist2.com/lisalist1/3505.html and associated replies in the LisaList1 thread
8088mph:
I had a similar problem, the picture was bouncing up and down but it was not scrolling like yours. I had to change three 16V 10uF capacitors on the analog video board. Take a look at the video board, if you can see corrosion from leaking capacitors, you should definitely change them. The potentiometers are another common problem, you can use contact cleaner on them or change them.
AlexTheCat123:
--- Quote from: 8088mph on April 20, 2020, 07:51:12 pm ---I had to change three 16V 10uF capacitors on the analog video board. Take a look at the video board, if you can see corrosion from leaking capacitors, you should definitely change them. The potentiometers are another common problem, you can use contact cleaner on them or change them.
--- End quote ---
Thanks for mentioning this! After looking at the capacitors, I noticed that they are bulging and probably need to be changed. I'll buy replacements in the next few days. I accidentally broke the vertical hold potentiomenter when reflowing the board (reflowing it didn't fix the problem) so I'll need to order a new one. Can anyone recommend a good replacement potentiometer that will fit in the board?
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