VOGONS

Horizontal Jitter/Flickering on Macintosh Color Display CRT

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First post, by oceangazer

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Hey all,

I have a Macintosh Color Display I picked up in a bundle of computers last year (came with a Power Macintosh 7200/120). Recently pulled it off the shelf and set it up as I'm intending to sell it, cool machine but I'm not much of a Mac person.

However, I did notice an issue with the display. After running for about 15 to 20 minutes, a horizontal "jitter" appears towards the top of the screen. I ran the monitor for about 2 hours, playing some Marathon 2 and generally poking around. The jitter didn't seem to get worse, but it certainly didn't get better.

I've tried to capture a video of what's going on, but be warned there's flickering/flashing images. The monitor runs at 67Hz, and the Nikon D800 I used could only get the shutter speed to 1/60. It does, at least, showcase the issue (second half of video zooms-in to better show the jitter):

https://vimeo.com/1162252132?share=copy&fl=sv&fe=ci

I'm curious if anyone here knows what might be going on?

Thanks much.

Reply 3 of 6, by Tiido

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This looks like something that a failing capacitor can cause, but there's also room for some bad solder joints or just being too dirty in the wrong place, the HV parts suck in all sort of things from the air. Going inside is inevitable regardless, a number of precautions are necessary when such a process is to be undertaken since a level of lethality is possible in several areas of the insides...and of course right tools and supplies are necessary too. This is something that is better done by someone with experience in these things.

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Reply 4 of 6, by oceangazer

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Tiido wrote on 2026-02-06, 22:35:

This looks like something that a failing capacitor can cause, but there's also room for some bad solder joints or just being too dirty in the wrong place, the HV parts suck in all sort of things from the air. Going inside is inevitable regardless, a number of precautions are necessary when such a process is to be undertaken since a level of lethality is possible in several areas of the insides...and of course right tools and supplies are necessary too. This is something that is better done by someone with experience in these things.

Thank you for the insights, I appreciate them.

Given the nature of CRTs and my limited experience, the best idea is for me to leave it alone and be transparent about the issue when selling it. Perhaps the next owner will be able to resolve the issue. Thanks again for your help.

Reply 5 of 6, by wierd_w

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Dirty / oily POT giving inconsistent values is another remote possibility.

A good cleaning and inspection is step 1 here, pretty much...

Reply 6 of 6, by oceangazer

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wierd_w wrote on 2026-02-11, 17:38:

Dirty / oily POT giving inconsistent values is another remote possibility.

A good cleaning and inspection is step 1 here, pretty much...

Thank you for the additional context, it is appreciated. This particular monitor had indeed been stored in a relatively dirty environment when I purchased it. So, no doubt there's some amount of grunge there.

I had a brief thought of cracking the case open, but my lack of experience combined with the potential danger put me off the idea. The best course in this case, I believe, is to inform potential buyers of the issue rather than trying to fix it myself (and possibly making things worse).

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