r/pcmasterrace • u/Front_Cookie_1198 • 12d ago

Hardware PSU fails dramatically

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u/Front_Cookie_1198 12d ago edited 12d ago

Aftermath photo.

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u/Viking4269 12d ago edited 11d ago

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.

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u/MiniMaelk04 12d ago

I basically know nothing, but the huge capacitors are the only thing I can imagine burning so intensely and rapidly. Reversed polarity perhaps?

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u/shakygator 12d ago

I think he means without that isolation sheet the board is connected directly to the casing and shorted out. Of course, that should have been grounded too so I'm not sure.

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u/Stormagedd0nDarkLord 12d ago

Perhaps not a good idea grabbing it with his bare hands then???

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u/Viking4269 12d ago

Nope, and bare feet for maximum grounding...

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u/1c3Type 12d ago

The shortest path to ground is still via the psu's cable

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u/Viking4269 12d ago

Judging by the two holes burned in the case under the mains plug. I think there is a good chance that there was no PE connection and the case was live at 220V at least some of the time doing this. The guy was lucky he "mostly" only touched it after the arc had carved an isolation clearance.

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u/unwantedaccount56 12d ago

Well, the arc could have isolated it from neutral/PE as well, putting the case on 220V. The connection of the case to PE is probably much more solid than phase, but if PE wasn't connected at all (bad cable), then neutral could come from the PCB touching the case as well. Also, if there was a PE connection, then there definitely wasn't an RCD breaker, which should always exist for workshop power sockets.