I posted this in one of the other unrelated 6850 threads, but figured I'd start a new thread to see if anyone can help me.
I'm having some bad issues crossfiring my HiS 6850's. For instance, here's a vid I took of the title screen of Far Cry 2. http://www.youtube.com/watch?v=nL8tnQtP6AE Notice the pixelated "blocks." When I turn off Crossfire and just use my card in the first slot, it runs fine.
Other bad things happen in other games. While crossfiring in LFD2, I get screen flickering effects, as well as bright green spots built into the textures. BF:BC2 also has the same particle effects as Far Cry 2 does. Again, when turning off Crossfire, all these problems go away. I'm pretty disappointed that I bought two cards and can't even get the performance I want out of them. Ah well, my first build. You live and learn, I suppose.
However, any advice would be greatly appreciated.
Intel Core i5-2500K Sandy Bridge 3.3GHz
2 - HIS H685F1GD Radeon HD 6850 1GB 256-bit GDDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX
MB ASROCK|P67 EXTREME6 (B3) P67 R
You can turn on triple buffering and vsync, but who wants to run with vsync on? This is what everyone told me to do to clear up the flickering issue with my AMD cards in crossfire. While this cleared it up for the most part, vsync introduces just enough response lag into a first person shooter that it's maddening especially in multi-player mode with first-person shooters like BFBC2 (my favorite game).
With the exception of the pixelation, although I never tried farcry 2, I had the same flickering issues you're having with my crossfire setup (and more). I couldn't stand that I poured that much money into it (for three cards) and got the results you describe above and then some. I kept waiting (for over a year) for the latest monthly driver to clear it all up. Through my expensive life lesson, I came to the conclusion that AMD cards run better as single cards.
PSU is 750 watts. Don't think that's the issue. Ran a stress test last night as well using FurMark. Didn't see any problems there either. Also tried a new crossfire bridge. I'll try switching the card slots after work today.
Just know when you switch the cards/slots, you'll probably have to re-install the drivers to get everything working. I tried all that when I had my crossfire set up too. Each time I added a card or while I was going through the troubleshooting as you are and changing the slot positioning, I had to re-install catalyst drivers or they wouldn't recognize all the cards properly. All my cards worked just fine by themselves though at lower single-card framerates.