Hashrate starts out high, then drops.

[Wolf0]

NaN.

[Waramp22]

Its normal for a cards hashrate to drop as it heats up. You are overclocking a card. Its like feeding an engine nitrous. They can handle some but there's a fine line to where they just get too hot with too much load.

Are you using auto-fan? I'd set the fan to 60-80 and tweak the temps/hashrates until they are solid, then leave it for 24 hours and see if it crashes.

[Kluge]

If it isn't a heat issue on the cards (I'm assuming you checked), it could be the PSU failing to meet demand. 750W output for what you're powering is cutting it pretty close.

PSU output decreases when hot. Maybe just give it a thorough dusting?

[fenican]

I had the same issue with one of my 7970's where it was slowing back to 680 kh/s instead of 760 kh/s after it got warm.  Setting gpu-powertune to +5 on my miner solved the issue

[fenican]

I had the same issue with one of my 7970's where it was slowing back to 680 kh/s instead of 760 kh/s after it got warm.  Setting gpu-powertune to +5 on my miner solved the issue

I have powertune at 20.

Guessing then it is the PSU failing to meet peak demand.  The strange thing is I'm running two 7970's nearly full speed (1080/1500) off a Corsair 650W PSU with no issues so I'm surprised 7950's would cause a problem with a 750W PSU.

I think I may have lucked out in the sense that Corsair tends to underrate their PSU's it can probably crank out 850W peak

[computerparts]

Try lowering the intensity or grab a cheap gpu and run the monitor off of that. I noticed some video cards running the monitor do not like high intensity.

[Malawi]

If it isn't a heat issue on the cards (I'm assuming you checked), it could be the PSU failing to meet demand. 750W output for what you're powering is cutting it pretty close.

PSU output decreases when hot. Maybe just give it a thorough dusting?

Actually, one of my 7870's runs at 102C and it's happy to pump out the kh/s.

Methink that sounds dangerously high.

AFAIK - It will work for some time, but the card will have severely reduced lifespan.