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Picked up an old, very dusty Macintosh 7100/66 from a guy in Cincinnati about a year or so ago. Worked for a while but one day I heard some crackling noises coming from within the PSU. Unplugged it very quickly and cracked open the PSU to find the devastating scene in the attached photo. I noticed one of the IC's was fried pretty badly, so I bought a replacement and installed it. However, upon plugging in the power supply a second time, the IC fried in the same exact way it had before. I've circled it red in one of the attached photos. I really have no idea how this PSU works, but what might be frying that little chip? I'm OK at soldering, but still pretty bad at diagnosing component-level issues. I also have a lower-end fluke multi-meter so I can check diodes, capacitance, and that sort of thing. In fact, I checked the two larger caps and they were still functioning. Thanks to anyone who can give some advice!


Edit: Just realised I put this in the Apple II Category by mistake. Could a mod help me move it to the PowerPC category? Thanks.



Edited by twillkickers
Put into wrong forum

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Hi, I can't help you much with troubleshooting, but generally in electronics just become something burns doesn't really mean it was causing the problem, it just means that something went wrong, somewhere, and this part was the one that couldn't take it.


The most common type of component to fail is electrolytic capicitors. They're often used as filters, and as they get older they dry out and don't filter as well as they used to. I have heard of that causing other components to give out like this.


This board looks quite badly damaged, though, I'm not sure how much time I'd spend on it.

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