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Bad mobo or PSU?

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i upgraded to an ASUS M4A79 Deluxe a few weeks ago and couldn't be happier. until now that is. i woke up yesterday and went to turn on my computer like always but it wouldn't go. it had been functioning completely normal before. shut down fine the night before. PSU is connected and on. everything is connected right. no changes were made from previous successful boot. btw PSU is an 850W Rosewill.

when i press the power button, both graphics cards' lights flash like they should, the fans light up and spin for about a second before turning off again, PSU fires up. basically everything works as it should for one second. this happens when when i use the case button and the button on the motherboard. after this initial power burst neither button does any thing until the PSU is reset. this leads me to believe the PSU is bad.

i tried the paper clip jumper trick on the PSU and it works. the fan i connected to it turned on and stayed on. this leads me to believe the motherboard is bad.

so do i call ASUS and try to replace the motherboard or is there some simple fix i am overlooking? thanks for the help!

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Motherboard Authority

Does the cpu cooler fan spin "for one second" before shutting off? Rapid shutdown can occur if the mobo detects a fan failure.

There are several failure modes for a psu, and its ability to run a single fan doesn't necessarily mean it can provide the clean power the mobo needs. When you say you "reset the psu" to get the system to pulse on, what do you mean?

You don't have onboard video, so reducing the system's power requirements to see if the psu will get it running isn't an option. (Although you could try booting it without the vid card.) The only other simple fix left to try is clearing CMOS which is 99% guaranteed to change nothing.

So the next step would be to swap in another psu and see what happens.

As you know your problem could be either mobo or psu. The general odds favor it being a psu problem.

by reset the PSU i mean flip the main power switch off and back on.

the power supply is over a year old (maybe closer to 2 years) but it worked fine for the 2 weeks i had this system running. like i said its an 850W PSU. the only other PSU i have access to is a 500W and i calculated my power requirements to be in the low 700W range.

so we are sure about this being a PSU issue? i just find it strange that this same PSU worked for over 2 weeks on this system. PSU's do fail though. and this one's getting older. i guess if you guys are sure i will order up another PSU.

here's my system. tell me how much juice you think i need. 850 should be big enough right?
ASUS M4A79 Deluxe
AMD Phenom II X4 940
8GB Kingston HyperX DDR2 800
2 ATi 4870 1GB in CrossfireX
2 500GB WD Caviar Black in RAID0
1TB WD Caviar Black
LG DVD burner
2 80mm case fanse
5 120mm case fans
2 140mm case fans

[EDIT] im looking at this Corsair 850W http://www.newegg.com/Product/Product.aspx?Item=N82E168...
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kojo87 said:
the only other PSU i have access to is a 500W and i calculated my power requirements to be in the low 700W range.


PERFECT! Pop that puppy in and power up - just don't run any 3D graphics. If you don't have the right PCIe connectors, pull one of the graphics cards. It doesn't matter. If the system powers up, we have identified the culprit, the psu.

kojo87 said:
so we are sure about this being a PSU issue? i just find it strange that this same PSU worked for over 2 weeks on this system. PSU's do fail though. and this one's getting older. i guess if you guys are sure i will order up another PSU.


Yes, these parts fail when they fail, not a moment earlier or later lol. No, there's no way we can be 100% sure it's the psu. Theoretically, a graphics card could have failed due to a thunder storm while you were asleep and shorted out the 12V on the PCIe bus lol.

But the test above is going to give us enough confidence to say you gotta write a check for the Corsair.

i guess the better question is are we sure its not the motherboard? im pretty confident that this board would not fail in that short of a time period. i've never had a bad experience with and ASUS product. the only board i've ever had fail on me was an MSI that was over two years old. when it failed i experienced much different symptoms.

i will try the other PSU (also a Rosewill and currently installed in another build) as big of a pain in the ass as that will be to rewire that build again. i feel pretty confident that this is a PSU issue though. it was my first instinct but i tend to assume the worst.
Motherboard Authority

If a four-legged creature has knocked down the corral fence, suspect a horse before hunting for zebras.

Sure, it could be the mobo, or several other things lol. But no need or reason to suspect those until we eliminate the most likely suspect, the psu.

i tend to assume its a zebra. my BIOS was acting strange and i thought my keyboard was going to hell when i realized the kpb jumper on my mobo was off. :p 

i plan on open benching it. i just meant its going to be a pain in the ass to take it out and back into the other PC it was in. its a smaller cheap Rosewill case (you'd think i'd learn but no) with the PSU mounting at the top. my main desktop case is a NZXT Tempest which mounts the PSU at the bottom and is quite easy to manage
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