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IBM PS/1 VGA color monitor with double images -- how to troubleshoot?

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First post, by biggieshellz

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Hi all -- I recently picked up an IBM PS/1 2121. It's one of those odd ones with the PSU for the computer inside the monitor. I have the computer working when powered from the monitor but displaying on another monitor, but the monitor itself is not working quite right -- see attached photo. There are two copies of the image displayed -- one at the top where it's supposed to be, and one about halfway down the screen.

Any ideas on how to troubleshoot something like this? Are there particular capacitors I should be looking at replacing here? Is this one where I might get lucky by taking the cover off and adjusting the vertical hold trimpot?

Thanks!

Reply 1 of 2, by mkarcher

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biggieshellz wrote on 2026-04-13, 19:54:

Any ideas on how to troubleshoot something like this? Are there particular capacitors I should be looking at replacing here? Is this one where I might get lucky by taking the cover off and adjusting the vertical hold trimpot?

Trying to adjust the vertical hold is definitely the correct first step. It seems the moinot syncs to 2/3 or 3/2 of the correct vertical refresh rate, so it is "way off". Nevertheless, it clearly syncs, which means a sync signal is arriving at the monitor, otherwise you would get a rolling image, not a double image. This can be caused if the vhold trimpot lost contact, so twiddling that pot should absolutely be the first thing you do. Only if you can't get the monitor to capture the correct vertical sync with that pot, it starts to make sense to dig deeper.

Reply 2 of 2, by biggieshellz

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That ended up being it! I opened up the monitor and moved around the vertical hold, and now I have a good image! Thank you!

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