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Not enough power to my 2 9600GTs in SLI

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May 11, 2008 4:08:06 AM

I posted this on the eVGA and CoolerMaster Forums, but have gotten no help. I use this sight extensively for research, so I'm here to gather a bit more knowledge :) 

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Alright... I've been fighting with this all day and getting no where. I spoke to an eVGA rep on the phone a little while ago, but we decided I should post here.

I got in the components for a new system today and have put it together. Basic components are as follows, running under XP Home:

XFX nForce 780i SLI 3-way SLI Motherboard
Pentium e8400 3.0GHz C2D Proc
Corsair XMS2 4gig (4x1gig) DDR2-800 5-5-5-12
2x eVGA GeForce 9600GT 512Mb in SLI
CoolerMaster Real Power Pro 750W PSU w/ 4 12V 19A rails (SLI Certified)

So... when I boot, I get an error that says that it has been detected that my graphics card is not receiving enough power and that it's performance will be rolled back to protect the hardware (or something to that effect). The PSU comes with 2 6-pin PCIe connectors, and each is going into a GPU. I have one optical drive and one hard drive at the moment, so I don't think 750W is too little.

When I run SpeedFan, I'm told I have 9.9V on the 12V rails. Everest tells me I have 8.3V. My BIOS tells me I have 12.2V. When I use ATI Tools, it says that my gpu clocks are at 650MHz and my memory clock is at 900MHz (so double that is the correct 1800MHz, since it's DDR3). I originally thought that it was just griping because it has incorrect voltage readings and that the fact that ATI tools was showing the correct frequencies must mean that it's not actually downclocking.

Then I ran 3dMark06 and got a whopping 1780. It was miserable. I pulled out one GPU completely and ran it again and was over the 10k mark... so something is definitely going on. My only guess is that it actually IS throtting back the GPUs under load, perhaps, and that I'm just not seeing it because I'm idling. Or maybe my PSU is bad... I just don't know where to start. To answer one easy question, no, I don't have another 750W+ PSU sitting around :(  that'd be too convenient.

Any ideas?

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Update: I checked the performance of the SLI setup in game and it sucked. I also took a multimeter to the psu and it confirms 12.2V on the 12V rail. I'm at a loss.

More about : power 9600gts sli

May 11, 2008 4:15:28 AM

if your 12v was falling that low, it would crash

did you try each card on its own in both slots?

you could try buying a new PSU at a place with a generous return policy.

my gut instinct says it power managment on the motherboard
May 11, 2008 4:18:14 AM

Hm... I didn't check both cards in both slots. I can definitely check that... would clarify if a card or the mobo was having issues. Will check. :)  Thanks!
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May 11, 2008 4:25:33 AM

i'm plannin on gettin the same motherboard and PSU, so let us know what happens lol. hope it isnt somethin a simple RMA cant fix
May 11, 2008 5:26:09 AM

Thanks for the advice, groo. Turns out, the PSU and Mobo seem to be ok, but one of the cards' auxilary power receptor is dead. It can't get any extra juice from the PSU, so the system was downclocking it for safety. The other is working fine alone, so I'll "limp" along one just one for a while :) 
May 11, 2008 5:30:15 AM

glad you figured it out. there are so many possible causes for everything.

the "limp" shouldnt be too bad with a 9600gt
!