MB fans come when atx power is turned on, and dont turn off!

Posted on 2005-04-22
Last Modified: 2010-04-26
I've just got another case for my Asus A8N-SLI, with a GTR 550w PSU, I've pugged everything in, and when I turn on the power to the PSU at the back, the motherboard/chipset/graphics card fans come immediatly on, although the computer is not booted up yet.  Pressing the on switch boots up the computer (WinX Pro), shutting down the computer shuts down windows, but the fans remain on until I switch off the power to the PSU.

Any ideas?

I've reset the BIOS settings to default, and still no joy.

Many thanks.
Question by:FalconUK
    LVL 69

    Accepted Solution

    Check the PSU manual to see if it has a feature that some power cables are always on, which I doubt.  I think your PSU is faulty, and it being part of a new case, you should exchange it.

    Author Comment

    Thanks Callandor, the new case and psu didn't come with any manuals, so I'll call the place I bought it from on Tuesday (mon being a bank holiday in Oz).

    The fans come on for a split second (which I recall from other PSU's I've had) then power seams to fluctuate for another second or so, where the fans spin up and down, then they come on fully.
    I was speaking to an IT friend of mine and he mentioned that some motherboards try to return to the last state they were in after a power fail, and that might be the reason its turning the fans on when it gets power. Does this sound possible?
    LVL 69

    Expert Comment

    Yes, that setting is in the BIOS, but it only happens immediately after a power failure.  It should not happen the next time after you shut down properly.

    Author Comment

    Just got back from town, they tried two other GTR 550w power supplies and they did the same thing.  They tried another type and that fixed it. Not too sure what type it was tho.

    Thanks for the help.

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