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Is this problem the motherboard or PSU?

Last response: in Motherboards
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February 23, 2010 7:28:43 PM

Hello, I have built a PC and there is a problem. When I flip the PSU switch at the bottom my LED fans light up and start spinning, and the lights on my ASUS Crosshair III mobo light up as well. The fans are connected to molex adapters directly into the PSU, however the CPU fan is connected to a fan header on the motherboard and it does not spin.

When I turn the PC power on my video card starts up at full blast, but there is no POST.

I did a test where I disconnected the PSU from everything except the molex fans, flipped the PSU switch and nothing happened. Then, when I plugged in the 24 pin power cord to the motherboard all of a sudden everything lights up and the fans start turning.

Is this due to a faulty 24 pin cord from the PSU, or is the motherboard somehow telling the PSU to leak power while it is supposed to be "off".

I even made a video to illustrate my point:
http://www.youtube.com/watch?v=zIKiwTGEXUk

I am leaning towards the motherboard being the problem, because if it was the PSU shouldn't my PC still POST?

Best solution

February 23, 2010 7:40:06 PM

This is definatly a problem with your motherboard...

check your bios settings....

Check to make sure all 6 pin/24 pin connectors on your mobo are plugged in....

Not posting is usually a hardware issue or lack of power issue.. however everything that is directly plugged into the powersupply works than most likely the problem is with the mobo (as it is not supplying the power in turn to the cpu fan)

so either a defective motherboard, or something simple as a cable not plugged in

some motherbaords need an extra 6 pin or 4 pin on top of the 20+4 pin connector.
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February 23, 2010 7:46:08 PM

Or maybe your powersupply is not strong enough please post your specs so i can better assist you....
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Related resources
February 23, 2010 9:03:16 PM

Seasonic M12D 850 watt

Radeon 5850

4 Gigs of RAM OCZ black edition 1600

Phenom II 965

Anyway, how do I change BIOS settings when nothing will even come on the screen?
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February 23, 2010 9:10:23 PM



sorry i wrot that before i watched your video....
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February 23, 2010 9:15:19 PM

im definatly leaning towars it being either a faulty mobo or you do not have the extra 4 pin plugged in.... please verify you have both the 24 pin and the extra 4 pin plugged in.. the extra 4 pin is on the other side of the processor...
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February 23, 2010 9:18:59 PM

Its not a four pin, its actually 8. Yes, they are plugged in.

Lets not even worry about posting for a second. My fans should not be spinning until the PC power is turned on, ever, right? Is this right here not proof that it is a faulty component?

I can always bring this to a computer store, but I am quite confident that after an hour of testing the guy will tell me my mobo's screwed and charge me 60 bucks.
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February 23, 2010 10:02:23 PM

yea if you have all power pins connected then yes your problem is indeed the motherboard!
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February 24, 2010 9:34:13 PM

Best answer selected by bootlegusher.
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February 24, 2010 9:35:03 PM

It turns out I had a front panel USB connector plugged into my sound card, no faulty equipment after all!
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