r/pcmasterrace • u/Front_Cookie_1198 • 1d ago

Hardware PSU fails dramatically

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u/SoulWager 19h ago

Not this time. You can hear the mains frequency in the arc, and the only output that should be powered is 5vsb.

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u/7orque 16h ago

So you’re saying this is on the input stage prior to the rectifiers?

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u/SoulWager 16h ago

Probably. I think if this was after the rectifier, the rectifier would have acted like a fuse, getting you a single loud pop instead of a few seconds of arcing.

It's definitely somewhere on the primary side though.

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u/ReaperAteMyPrawnsuit 8h ago

This thread is too electrical smart for me to understand what’s going on

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u/4236W 8h ago

Something between the power switch and the thing that makes the wall power into PC power wasn't made right, and wall power got somewhere it shouldn't go

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u/Flying_Dutchman92 4h ago

Thank you for that translation

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u/OutlandishnessHour63 2h ago

That isn't a bad translation. I like it 😊 To make it a wee more complicated but more comprehendable when reading the raw jargon.

A rectifier takes AC, or alternating current, (ie; electricity out of an outlet) and concerts it to DC, Direct Current. (is; power from a battery)

What was being plaused upon earlier: The theory for the short is that the power moved from AC and before it hit the rectifier, it shorted to the case of the power supply due to a missing piece of insulation.

Comments back and forth were discussing whether it was pre-rectified or not based on how the arc sounded and occured and based on the fact that the circuit breaker for the outlet (AC power) was not tripped.

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u/Flying_Dutchman92 1h ago

Today I learned about circuitry, thank you for expositioning:D

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u/SoulWager 8h ago edited 8h ago

What happened is pretty simple, mains wires poked through the board, weren't trimmed after soldering, weren't blocked by an insulating sheet, and touched the case: https://i.imgur.com/SLsQmmu.gif

The discussion above is about why other possible failure modes are unlikely. After getting on to the board, the power goes through some filtering and protection circuitry, then through a rectifier(4 diodes in a single package) that turns the high voltage AC into high voltage DC. Then the high voltage DC gets chopped up into much higher frequency AC, before going through a transformer to drop it down to low voltage high frequency AC. This then gets rectified to 12v DC before getting converted to the other voltages. Usually anyway, there are other ways to design a power supply, and there will be a separate similar power supply just for 5vsb(this is always on, so your computer can turn itself on when you press the power button).

Anyway, back to the rectifier, semiconductors often have relatively thin bond wires connecting the silicon die to the rest of the package, that would get vaporized in a few milliseconds if you tried to push this much current through them. This board also has an actual fuse, but the short happened before the power got that far.

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u/shakygator 7h ago

Nice overlay

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u/stuck_in_the_desert 1h ago

There was too many pixies, which caused it to stop choochin’

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u/SoulWager 8h ago

I found a review with PCB photos, the burn holes are right under where the mains enters the board. Probably wasn't trimmed after soldering, and missing insulation sheet between pcb and case.

https://i.imgur.com/SLsQmmu.gif

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u/Inaniae 18h ago

Correct.

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u/Good_Background_243 5h ago

Oh shit yeah I hadn't noticed it but on a second watch yeah that's definitely high-frequency AC, the arc sounds fuzzy.