Intermittent Power Supply

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Joined: Jul 30 2011
Posts: 86


I have a problem with an Apple II power supply. It started after running the machine for about an hour with a buzz or rattle (possibly the transformer?). I removed the supply and switched it on again, observing the board. It ran ok so this fault obviously only comes to light under load. I plugged it back into the motherboard and ran it again. After a few minutes it rattled again but after a little prod around it seemed that R4 had a dry joint as a slight movement stopped the noise. I resoldered the joints but noticed that there was evidence of over heating around the resistor pads. Powered up again and ran for a while but another gentle tap on R4 re-created the problem. Thinking R4 was failing, I replaced it with a 7w version as i could not get a 2w. Ran it again but still the intermittent rattle.

Would any other components cause this problem that I need to look at, or could this be a general dry joint issue and R4 was just a red herring?
(Although the overheating evidence suggests otherwise)

I need to fix this really as this is the only one I have at the moment! (I have just bought a 120v one from ebay but may take a while to ship to the UK, and yes - I do have a step down transformer!

Thanks in advance.