Both of my 7900GT's work fine by them selves but not in SLI WHY?

I have 2 XFX 7900GT's that I'm trying to run in SLI but when ever I try and load a game I get artefacts all over the screen and I have to alt + tab in and out of the game and that fixes the problem most of the time but I am getting poor performance. I initially thought that one of the cards had failed so I took one of the cards out and used one card which gave me better performance and no problems. Being methodical I tried that card in the other x16 PCI-E slot and again it worked fine. I then swapped the cards and low and behold the other card worked fine as well by its self.

This really confused and annoyed me as I was sure one of the cards was faulty. I reinstalled both of the cards but Intentional left out the link bridge between the two cards as this was the only component I hadn’t tested but I got the original problem I installed the link bridge but it hasn't helped.

I have pics of my Rig and the error but I don’t have any web space to load them to so if some one would be kind enough to host the pics I'd be very grateful.

My system specs are as follows

Asus A8N32-SLi
AMD X2 4400
2GB Corsair RAM
Seasonic 600W PSU
2 XFX 7900GT
Creative X-Fi Platinum
2 Pioneer 111 DVDRW

Thanks for the help Dan

 

Drop me a PM, can host images.
Did you run a single card/have windows and/or drivers installed before adding the second card?
Also, run 3dmark 2006 on both cards individually. See if you get any artifacts in the "deep freeze" test (its the last one)

 

Have you tried a new SLi bridge? It could be knackered if the above come up strangely.

 

I doubt it... I've accidentally run SLI without the bridge attached - there were some screen sync issues, but no artifacting.

My bet is that there's a heat-related issue coming up with both cards installed and cooking away in SLI.

 

Yar, it was mentioned in the post that the artifacting still occured even without the link bridge attached (if i read it correctly)
If this IS the case, then the issue must be caused by the top card/one with video output connected as the other card would be sat doing jack all if the SLI bridge wasnt present.

 

Hi guys thanks for the replys. Like I said in my origional post by them selves the cards work fine put them together and they wont play games at all. Windows works fine but if you push them with a game nothing.

 

PSU issue? Have you tried another?

 

Can you confirm, putting both cards in the PC WITHOUT the SLI bridge still gives you the same issue please?

 

To confirm I get the same problem with or without the SLI Bridge. I havent tried a different PSU might be worth a look although I do have a decent PSU and I dont get the feeling its faulty

 

Have you checked temps and BIOS updates?

 

By decent PSU you mean?? Does sound like a PSU or heat problem tbh. Could be a board problem: got the latest BIOS/latest forceware??

 

Check the first post, he's running a 600w seasonic. Wouldnt think its a power issue, doesnt sound like one either.
There's good spacing between the top card and the soundcard below, doesnt look like a heat problem tbh. With the SLI bridge removed, can you plug a monitor into the lower of the 2 cards and have a look at the output from there?

As suggested, also worth checking bios versions etc are up to date.

 

Sorry it was buried in the specs I didn't see it

 

I'm still really confussed about this problem its my making my head hurt.

 

Can you act on the suggestions people have made mate. Might help us get to the bottom of things

 

Sorry I have the latest bios for my Motherboard and I have the latest forceware. My temps are fine I dont have numbers to hand but I have checked them.

 

Note that 12V molex connector on your motherboard? Right next to your 20-pin motherboard power connector? The one that has NOTHING plugged in?

That's called the EZ-Plug. Its job (amongst others) is to feed your SLi cards with sufficient juice to operate together. If you use only one card, there is no problem. But unless you already have a line plugged into the square 4-pin connector in the top left corner of your mobo, you need to have a 12V line plugged in the EZ-Plug if you want to use two cards in SLi mode.

 

How did I not notice that Good one nexxo

 

I do have the 12V square plug connected to the mobo that’s why I didn’t connect the molex up. That was my understanding from the mobo manual. I would like to clarify as I am concerned that ill fry something by connecting that as well.

Also when I connect the monitor to the lower card I get the same problem.