Unstable hashrate 7970's - goes up and down

[Spetznaaz]

Hi, i was wondering if someone may be able to help me.

The hashrate on one of my 7970's is stable (GPU 0) without a monitor, but the other goes up and down a lot (GPU 1), and when i switch the monitor over to GPU 0, it becomes unstable a bit, but not as much as GPU 1 and GPU 1 is still unstable without a monitor just slightly less... - i fixed it once just by increasing voltage, but it seems to be happening again.

Anyone know what it may be?

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[AzureEngineer]

You're probably using high intensity on the GPU that is outputting to your monitor. An idle desktop can still take up a noticeable amount of processing power and thus your hash rate will fluctuate. Lower intensity can resolve it.

You can also use a program such as MSI Afterburner to monitor your clockspeeds. If you've overclocked the card too much with too little power, the clockspeed will not be stable.

[bobsmoke]

I have 1 7970 and after some testing it looks like the best intensity is 7 using cgminer.
Other than that I normally use 85% Fan and 1180Mhz Clock plus 1000Mhz Memory

[Spetznaaz]

Intensity 7 put me down to 17 Kh/s from 730Kh/s lol.

My current intensity is 13, 12 gives 420 Kh/s, both a lot lower than i'm getting with -I13 and the unstableness.

As i say, when i swap the monitor over, GPU 1 hashrate is still unstable. It will go up to 730, then hang there for a bit then suddenly jump down to 660 etc.. But GPU 0 is completely stable when no monitor is plugged in to it.

[AzureEngineer]

That happens to just about all cards (in my experience). You'll have to run the card for at least five or so minutes to get a marginally accurate reading of hash rate.

[Spetznaaz]

Hmm but the thing is, they are identical cards, and one of them is completely stable without monitor plugged in, the other is very unstable (varying by about 50-100 Kh/s) monitor plugged in or not..

Edit - No idea what i've done but i've been playing around with setting and now they are both stable at 710.. weird.