[SOLVED] Power supply works on one motherboard but not the other, but the other motherboard works

Nov 1, 2018
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I've run into a pretty bizarre situation and am not sure what to make of it, so hopefully, someone here can help:

My friend's computer isn't powering on. I troubleshooted it, using my computer to help. His motherboard wasn't getting power (checked using the motherboard USB ports). I made sure everything was plugged in correctly, and it appeared to be, so I then plugged his motherboard into my power supply, and the motherboard became powered. After checking with the original power supply one last time (still didn't work), I recommended a replacement power supply as I was sure that was the issue. However, the new power supply also does not power the motherboard, and after some additional experimentation, we discovered something quite interesting:

  • His original power supply powers my motherboard, but not his
  • His new power supply powers my motherboard, but not his
  • My power supply powers both motherboards
You can see where the confusion arises: we can't seem to find a consistent point of failure. Both motherboards are capable of receiving power and all power supplies are capable of giving it.

What could we be missing? We're honestly pretty stumped. (It's not the outlet or the power cables, we checked those; and we are using each power supply's respective motherboard cable, not mixing and matching)
 
The real test is if the motherboard will boot into the bios.

How are you trying to start the motherboard?
Some will have a pwr button that you can use.
Otherwise, you need to use the case power on button.
Possibly there is something wrong with that connection.
Alternatively, you can momentarily short the two pwr pins on the motherboard front panel header.

Of course, you could simply swap power supplies and get both of you running again.
(Not such a good deal for the Seasonic owner)
 
Reactions: stubbsnc
Nov 1, 2018
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His old one: EVGA SuperNova NEX650G1
His new one: Thermaltake Smart BX1 RGB 650W
Mine: Seasonic Focus Plus 850 Gold (SSR-850FX)

Also, I realized I failed to mention something in my original post - his power supply has been successfully powering his computer for years, this isn't a freshly built machine. It was unused over the summer while he was traveling and didn't turn on when he got back.
 

gn842a

Respectable
Oct 10, 2016
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Testing power through the USBs may not be an adequate test. Perhaps you should test what actually boots. You may have stumbled across some bizarre failure mode which allows his mobo to meet the USB test with your Seasonic. Try an actual boot all the way into the OS. That puts more strain on the psu. Greg N
 
The real test is if the motherboard will boot into the bios.

How are you trying to start the motherboard?
Some will have a pwr button that you can use.
Otherwise, you need to use the case power on button.
Possibly there is something wrong with that connection.
Alternatively, you can momentarily short the two pwr pins on the motherboard front panel header.

Of course, you could simply swap power supplies and get both of you running again.
(Not such a good deal for the Seasonic owner)
 
Reactions: stubbsnc
Nov 1, 2018
6
0
10
0
After further testing it wouldn't boot up even with my power supply attached, so we concluded it was the motherboard. We replaced that and it now works, so yay
 

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