No power up... is mobo dead?


I have a KV7 with AMD XP 3200+, nvidia 6800ultra. The machine was running fine, then suddenly powered down itself. Now when I try to switch it on, I can see the PSU fan, 6800 fan, and the Northbridge fan start up for about half a second, but then it goes completely dead. (If I don't dis/re-connect the mains lead, I get no attempt to power up at all.) Sometimes, but not always, I hear a brief beep as it tries to start.
I've tried clearing the CMOS, and I've tried disconnecting everything but the 2 ATX power leads.

I did add some RAM a few days ago, but it has been running perfectly. (I've tried all the ram in another machine and it's OK, and I've tried starting without the new ram.)

Is this most likely the motherboard?
Could a dead CPU cause these symptoms?
I wouldn't have thought it was the Power supply as it's a farly new Akasa 460, and the leds and fan seem to try and come on. But who knows.

I could buy another KV7, but thought I'd ask around first in case I'm barking up the wrong tree?

Any clues appreciated.

5 answers Last reply
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  1. I'd try a different power supply first. But more than likely it's the motherboard. I had the same thing happen to me with a refurb board after 4 days.
  2. Thanks for the feedback. Yes, I guess it's cheaper to try a new power supply first. Interesting that you had a similar experience though.

  3. You might also take the board out of the case, and do a bare bones post on a phonebook. Just one stick of memory, video, and cpu/heatsink. This will almost confirm the problem. I've never had a cpu fail completely unless the heatsink came off. I had a barton 2500 overheat and pop some of the internal leads. Now the multiplier setting is lower (from 11.5 to 8.5) and the L2 cache dropped from 512 to 256, but the cpu still runs fine at 1700. Cpu-z reads it as a thornton instead of barton.
  4. No, I've never had a dead CPU either, so I guess it's the least likely culprit.
    I tried what you suggested, and the symptoms remain the same.
    (BTW, I don't have to have a video card connected do I, to at least confirm powering up?)

    I've ordered a Seasonic S12 500w, which has very good press. If it turns out to be the mobo, at least I'll have a worthwhile PSU upgrade.
  5. ** UPDATE **

    Fitted the new Seasonic 500w PSU... the mobo fan, cpu fan and PSU fan all powered up and stayed on. (This was with the board isolated, 1 chip ram, nothing else connected.)

    BUT. The mobo immediately caught fire! (To be precise: a small black plastic component on the edge of the board nearest the PSU, about 6mm square labelled 'Q1' caught fire)

    So the mobo's almost certainly fried, right? But the fact that the PSU stays on makes me think the old PSU must have been dead anyway.

    My guess is that a fault on the board fried the old PSU, and connecting a new PSU has somehow exasabated the existing fault and blew the board.

    Any speculation about what might be going on is welcomed.

    I have no choice but to buy another board, but the question is:
    1) Is this a vicious circle... might I have damaged the new PSU in such a way that it might damage a new board?

    2) Is the CPU likely to be a gonner? If so I might as well abandon the Socket-A board/CPU and just upgrade to a more modern system.

    3) Anyone know what the 'Q1' is?

    4) Why is the mobo normally grounded to the case... and was it therefore safe to unground it?

    Thanks for any clues.

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