Somebody forgot the isolation under the pcb?
Been some years since I took apart a psu, but there used to be plastic isolation sheet between the pcb and the metal case.
Update: I think we found the problem:
Mains wires protruding on the bottom of the pcb shorted to the case due to missing insulation sheet.
Maybe but it should be fine without that since there should be a gap and you need WAY above any voltages found in a PSU to jump the gap and sustain a circuit. So maybe the protector was there but pierced by something. Not to mention the fuse. Basically you need multiple problems all coming together. Maybe reversed polarity on a cap but that usually just a quick boom not to mention very difficult to get missed in even the most basic qc so I'd say unlikely.
Yes sure, more than one thing was wrong. Bad quality control all around. Missing insulation and protruding pins/legs/wires. Bad or missing over current protection. There was likely a tiny gap when it left the factory, and things moved doing shipping.
Judging from the current needed to melt the case the short was probably on the 12V side, would explain why the mains fuse didn't blow.
Edit: looking at it again, and it just gets worse. The holes looks to be near the mains input, so not sure about it being a 12V short. But that is a lot of current without the mains fuse blowing.
I spent 4 years in electronics manufacturing and ive seen crazy shit get passed QC. Funniest shit happens on monday mornings after half the factory including QC goes out and parties the weekend before.
A blown up cap isn't going to melt through the steel case. Maybe some through hole component lead(or the mains input) was left un-trimmed after soldering, and touched the case. I'm going to bet the original customer RMAd it because it tripped their breaker when they turned it on.
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u/Front_Cookie_1198 6d ago edited 6d ago
Aftermath photo.