Computer shuts off randomly. Does not restart until power cord unplugged & replugged. +12V rail climbs to +14V...

Okay some context: About two months ago, the fan in my Corsair VS650 PSU started making a loud cackling sound. I replaced it with the Seasonic M12 II 620W. For a month, no problems. Two weeks ago, my computer started shutting down randomly, and would not turn on until I unplugged/replugged the power cord (or shut off the PSU long enough for the mobo power button to turn off). The next day, the computer fired up normally so I didn't look too much into it.

However, earlier today, the issue presented itself again so first thing, I decided to test the PSU. I tried out the old Corsair PSU (its fan no longer cackles oddly) and the computer worked for 10 minutes before shutting off. During the 10 seconds the computer turned on after that, I went into BIOS and noticed that the reading on the +12V rail begins increasing steadily and once it reaches the 14V mark, the computer shuts off. I tried the newer PSU, same thing. I assume the PSUs are both fine, and the motherboard is fried?

i5 3570K
Gigabyte Z77X UD3H
GTX 970
8GB Kingston RAM
Seasonic M12 II 620W
9 answers Last reply Best Answer
More about computer shuts randomly restart power cord unplugged replugged 12v rail climbs 14v
  1. What happens if you unplug your graphic card and run on integrated?

    Go into BIOS and see if 12V still go toward 14V. If so, then yes, your mobo probably has problems.
  2. Just tried doing that. For the first 3 minutes, fine. And then that slow ascension to 14V, and shut down.

    So I can be sure that it's the mobo, right? It would be saddening to get a new processor/mobo only to find out that both PSUs were faulty - but I suppose that would be too much of a coincidence.
  3. How confident are you with a volt metre? I'd measure the 12v voltage on a spare Molex plug. If the voltage is creeping up then its the PSU, if the voltage on the meter stays at 12v while the motherboard reports an increasing voltage Id say its a motherboard fault. The motherboard does not control the psu voltage, the psu regulates itself
  4. Not very. For starters, will need to get one. Will look into it and report back.
  5. Update: I got the voltmeter, turned on the computer, Hardware Monitor showed a slowly ascending voltage on the +12V rail, and then, finally the whole damn thing shut off before I could get the voltmeter ready. After that, it stopped POSTing altogether - mobo/fan lights flicker on and then turn off until the power is turned off and on.

    I used the paperclip test on the PSU and checked the voltages. All of them are in line.

    Does this finally confirm it's the mobo that's at fault? Or is there is a remote chance that the PSU cannot handle load? (But then, in that case, the computer should at least POST, right...?)
  6. not necessarily.

    How many storage do you have? Hard drives?

    Is there a memok or clr mos button/header you can use to clear cmos? to get the system to post again?

    At this point I suggest rebuilding your system from the ground up. Take everything out of the case. Then vacuum the empty case. Compressed air or something to shake the dust off from mobo. Clean/replace any dusty fans. Then rebuild dust free.

    It may help.
  7. I was going to do what you said but didn't have to (not yet). Came back from work, the computer POSTed and has been working normally for the last hour.

    This is frustrating. I know this computer will turn off on me again but I can't troubleshoot right now because whatever part is dying keeps sputtering back to life.

    Meanwhile I've hooked the voltmeter to one of the 12V rails. When and if Hardware Monitor registers the increase, I will keep an eye on the reading. Hopefully I can rule out the PSU being a cause of the computer failure, and isolate the mobo as the problem.
  8. Best answer
    It's actually in order of possible culprits.

    1. short circuit

    2. dust

    3. mobo cmos battery

    3. mobo
  9. Darthutos said:
    It's actually in order of possible culprits.

    1. short circuit

    2. dust

    3. mobo cmos battery

    3. mobo

    Thanks. Changed the battery and it worked for a day. Then stopped completely. Took it all apart, and still would shut off after being on for a second or two. RIP Mobo.
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