ATI CrossFire instability and horizontal bands?

Solution 1:

This was a tough one.

After many hours of trial and error, someone mentioned to me that overclocking could be the issue:

overclocking can create issues with dual card setups (both CrossFireX and SLI.) You have to be careful about PCIe timings.

I thought overclocking couldn't possibly be it, since this system has been ultra stable for MONTHS with the current settings.

But setting BCLK to 100 (default) from the "auto extreme overclocker" override of 103 and not overclocking does seem to have worked. I was able to play several BF2:BC rounds with no issues, though I did see a hint of the horizontal banding at one point, it went away by itself.

So, watch out for any PCI Express overclocks when running an ATI CrossFire video card setup!

edit: additionally, I was seeing some other .. oddities .. that were resolved by setting the two video cards to the exact same clock and memory timings in the Catalyst Control Center AMD Overdrive section (although they are both 5780 cards, obviously, they came from the manufacturer with slightly different clock and memory timings). Thus, I also strongly recommend making sure both cards in Crossfire have the same settings.