Very strange issue.

[Rick]

So i've got 2x 6950's running on an Asrock m3a770de motherboard. Windows XP sp3, 11.7 drivers and using Guiminer. I've used both these cards and motherboard in the past without issue with the same power supply.

I have a seperate guiminer tab for each gpu, as well as seperate workers on my pool and using 2 monitors. I start one card, 360mh/s. All is normal, but then I start the second card and it begins "leeching" from the 1st card's mhash/s. Suddenly I'm getting about 100mh/s from one card, and 260mh/s from the other. It appears the cards are sharing the total power of one of them :\

I have everything overclocked in afterburner, but when I check CCC and GPU-Z it shows one of the cards is stuck clocked at 500mhz. This is "2D" mode as far as I know. I have several other 6950's, and have tried them, no matter what card I put in this rig one of them will be forced into 2D mode and I get these weird results when trying to mine.

I've messed around in the bios to no avail, ran the cards on their own and all works fine.. i'm stumped..

[TalkingAntColony]

Try:
- Booting to LinuxCoin (https://en.bitcoin.it/wiki/LinuxCoin) and mining from there
    If this fixes the problem, then your issue lies within Windows
- Ensure no crossfire settings are enabled. Both cards should run independently.
- Run without overclocks and see if same symptoms occur.

[Rick]

Thanks, I've tried with stock clocks, and i've also made sure no crossfire settings are enabled. I'l boot into linuxcoin like you said.