CPU or Motherboard fault?

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Hi. Hoping somebody could give me any pointers...

I'm trying to rescue a dead pc, and by swapping compatible parts around with
another pc - including the psu - I'm left with the cpu or motherboard being
the problem.

I'm now trying to narrow it down further so that I can replace the relevent
faulty part but this is where my 'expertise' fails me.


When the pc is switched on the cpu fan spins for about half a full turn and
then stops. I get no beep codes and there's no activity anywhere else on the

However, if the ATX 12v power connecter to the cpu is not connected, the
cpu/case fans spin into life and the graphic card and case lights switch on.

I guess my question is...Is this a typical symptom of a dead cpu or could I
still be looking at a motherboard fault?

Thanks in advance.


Re: CPU or Motherboard fault?

Lee Coleman wrote:
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For the fan to stop that fast, would be one of two things. Either the
PSU has detected an overload, and switched off. Or the THERMTRIP signal
from the processor, has triggered, and switched off the PS_ON# signal.

Have you checked that:

1) The CPU has thermal paste on it.
2) The CPU heatsink clip is applying pressure.
3) If the processor is an AthlonXP S462, that the heatsink is turned the right
    way. One of the two possible orientations, leaves part of the processor
    silicon die, exposed to the air, and uncooled.

If you had a clamp-on DC ammeter, with "peak hold" readout, then you
could check the ATX12V cable for peak current consumption. That would
tell you if this was a Vcore problem. Most people will not have test
gear like that to use, meaning just try more component swaps until it
is fixed.


Re: CPU or Motherboard fault?

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Thanks for your reply Paul,

I didn't put my specs as it was more of a general question but if it helps
it's a:-
Core2Duo E6600 cpu, A gigabyte GA965p-D3 motherboard, and a Coolermaster
650wt power supply.

It's a fairly new self-build pc that was working fine for a while.

Since I wrote my original message, I've also tried a different heatsink
(with paste) and a different psu. I'm still getting the same problem.
Unfortunately, I don't have any of the tools that can test for currents.

When the system was actually working I did keep an eye on the cpu
temperature and it never went above 35 degrees - so unless something strange
happened when I wasn't looking, I don't think it's a heat issue.

Normally I'd be fairly confident this is a motherboard problem, but it's the
fans and lights coming on when the cpu power lead is disconnected that's
throwing me.

Thanks again for your help.

Re: CPU or Motherboard fault?

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Its very rarely the cpu unless you have been
doing some very gung ho overclocking.

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Thats usually due to the power supply deciding that the motherboard
is loading a supply rail too much so it shuts down immediately.

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Then likely the high load is on that connector.

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Nope, they dont die very often and they dont produce that set of
symptoms when they do. If its a dead cpu the fans should all run
and the hard drives spin up, but you dont get any sign of life from
the cpu at all, no evidence that its running, no attempt to POST etc.

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Yep, its almost certainly that if you have eliminated the power supply.

Check for visible bad caps on the motherboard.

Re: CPU or Motherboard fault?

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Thank you Rod. That's a great help :-)

Re: CPU or Motherboard fault?

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Indeed. You can check this by looking to the bigger caps around the cpu. The
top shoul be flat. If they are bold, you found the problem. And actually,
this happens oftenly, since a Chinese manufacturer has sold many thousands
of out-spec caps to mainboard manufacturers, including the best. If your
board is out of warranty, you could try to replace all those bigger caps
(about 10 to 12).

Re: CPU or Motherboard fault?

Thanks to everyone for their help......

After having it checked out by my local pc shop it turns out that it is
indeed the motherboard that's gone .... unfortunately, it's also taken the
cpu along with it.

They couldn't confirm what caused the problem in the first place (the psu
was fine and the heatsink was aligned correctly) but luckily I'm still under
guarantee so replacement parts are on their way.

Thanks again.

Re: CPU or Motherboard fault?

On Sat, 25 Nov 2006 19:14:30 -0000, "Lee Coleman"

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Be cautious, it's very unlikely to have a board kill the
CPU.  I suspect the shop is either incompetent (and has
either killed your CPU or misdiagnosed it), or has decided
they can sell you a new CPU.  Don't get me wrong it's not
impossible to kill a CPU but the vast majority of the time a
board fails the CPU doesn't.

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