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SLI issue with 7950GX2 and the HX520W PSU


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I just bought the HX520W in order to fulfill the needs of my power hungry 7950GX2 card.

I used a noname PSU before and I sometimes experienced poor performance when running certain games.

The old PSU didn't have any information about amps on it, I only knew it was 450W so I really don't know if the performance problems I was experiencing had anything to do with power shortage but after reading about the power needs of the 7950gx2 I decided to upgrade anyway, just to be sure.


Before I decided on which PSU to get I used the "Power Supply Search"-function on the Corsair homepage and it recommended the HX520W for my system.


After installation everything seemed fine until I started a 3D application and this error message appeared: "d3derr_notavailable".

I ran the dxdiag tool and ran the direct 3d test app and it couldn't start any of the tests due to the same problem - no 3D support available.


After reinstalling drivers and pulling and pushing cables around in the cabinet for a while I tried disabling the SLI-mode in the Nvidia controlpanel and 3D-apps started working again.


Apparently my card won't run 3D apps in SLI with the HX520 but it works with my old PSU (with some poor performance under heavy load).

I reconnected the old PSU and tested SLI to be sure and it works so it's not the 3D card that's broken.


I suspect that the SLI problem is due to power shortage from the HX520 but the power supply search function on your homepage recommended this PSU for my system.


I can't return it to the store where I bought it and upgrade to a more powerful one since they only do returns if the box is unopened.


How should i proceed?


Thanks in advance


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I do not know the exact maximum power draw for that card but it looks like it has a single PCI-e connector which would mean the card could draw 150 watts max. Each 6-pin PCI-e connector can support 75 watts and the PCI-e slot itself can provide an additional 75 watts. Even with both cards running full blast that would be 300 watts for video, leaving you 220 watts for the rest of the system which should be plenty. If there is a problem relating to the PSU, it is unlikely that it is being caused due to lack of power. The HX520 is rated to deliver 520w at 50 degrees Celsius, which is hotter than your system should ever get, in real world conditions the PSU would be able to supply more than its rating.


I would suspect that since the old PSU works and ours does not that there may be a component going out of spec or overheating, and our PSU is detecting it while the older one is not.


At any rate if you would like to try getting the unit replaced we can do that for you. Please use the On Line RMA Request Form and we will be happy to replace it. Be sure to check the box that says “I've already spoken to Technical Support and/or RAM Guy.”

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Thanks for your quick reply!

(and yes, the 7950 gx2 only has one pci-e connector)


I've done some reading on this and from what I understand it's not only the watts that matter but also the amps.


"The minimum recommended power supply for a single GeForce 7950 GX2 is 400W (with 12V current rating of 27A)."(copied from Nvidia's home page)


So the HX520 can certainly provide the watts required, but can it provide the amps?


The HX520 has a max load of 18 amps per 12v rail and I can only connect one to the card - if the requirement is 27A for the 7950, is that enough?


I've tried to find info about this stuff but a lot of it is pretty hard to understand. Is it the combined amps of all three 12v rails that nvidia refers to or is it the amps of the single 12v rail that goes in the card..?

If you could help understand this a bit better I would greatly appreciate it!



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