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Cleaning IBM PS/2 Type 30 PCB

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First post, by Jotschi

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I found an old IBM mainboard on a flea market tour. It was initially very dirty so I gave it a quick bath with some soap and warm water. I rinsed it off with IPA to displace the water. After drying it became very "milky". When I use q-tips with IPA on those areas the tip becomes very dirty.

I think it is dirt on the PCB. There is also a place where the speaker (SP1) got ripped off. At that area the PCB is clean. That leads me to the conclusion that the IPA did not harm the board. Otherwise the area should also be affected.
Has anyone encountered this before? Any suggestions on how to clean it?

The photo show the issue with some areas already being dry and milky.

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Reply 1 of 3, by Horun

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I saw the picture and think there was a film on the board that the IPA altered so when it dried it turned milky. Have seen similar before.
Use Q-Tips or paper towel with a bit of IPA or Windex and you should be able to get it off.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 2 of 3, by luckybob

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I've always washed boards in hot soapy water. Dawn I'd my go-to. I also will goto town on it with a stiff bristle hand brush. Standard rinse with distilled water to remove any minerals from the water, and a 2nd rinse of 99% ipa.

It is a mistake to think you can solve any major problems just with potatoes.

Reply 3 of 3, by Jotschi

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It might be a bit crazy but I just added oil to the surface of the PCB. That cleared up the milky surface. I know about oils being potentially conductive but I only used 4 drops of sewing machine oil for the whole surface.
I'll update this post when I have fixed and tested the board. There are still a few ripped traces I need to fix.

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