I think 3 5970 is too much of a power draw on the PCIE bus. the limit is 300w per. Overclocking to 900 uses to much power.
Each PCIe slot can pull 75W however AMD has designed their cards to reduce the draw on the PCIe bus (in favor of PCIe connectors). This is because the connectors are more reliable source of power.
8pin = 150W
6pin = 75W
bus = 75W
I have never had a 5970 pull >300W. The 294W is AMD TDP spec (as in the max heat the card can handle without a dangerous failure). That doesn't mean the card draws 294W. At 100% load I measured (using kill-a-watt) 248W draw.
I have GUIminer
1075V
830 clock
500 mem clock
cool master pro PSU 1200watts
What is your power draw @ the wall? I guarantee you it is no where near 1200W. Probably somewhere around 900W - 1000W.
I am using this power supply.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817153148
Maybe I was wrong about 850W. I am going off memory. Once I got the system solid I removed the kill-a-watt to use on my desktop (which I am also fiddling with). I will recheck the wattage tomorrow but I am sure it isn't 1200W+.
Bringing your mem clock down to 300 will reduce heat & power output significantly. The difference between mem @ 500 and mem @ 300 is probably 20W a card. When I setup this rig I couldn't go below 300 but I haven't check recently and I saw a thread where someone was running 5970s @ 200 Mhz memory. I may need to revist my settings.
If you can't push the system further heat is likely your problem not power draw. The only way to know for sure is measure it all the wall with a meter like "kill-a-watt". In computer bios turn off everything you aren't using. Onboard sound, EIDE controller, etc. They may not be much but each pulls some power and likely is doing nothing. If your motherboard has onboard video make sure that is disabled too. Your CPU should be lowest power model you can find. For AMD Sempron runs @ 45W max and idles at half that. You can underclock/undervolt it (depends on MB BIOS options) and cut another 10W right there. Using linux distro and usb drive saves some power too. Windows loves to use swap file for no reason and HDD is going to pull 5W or so. It may seem like nickles and dimes but all those watts add up.
If you do nothing else work on getting mem frequency down. Running @ 500MHz is just burning up cash and limiting your overclock potential.
If the voltage regulator gets too hot it will lock up the system. Usually when GPU core is too high it results in artifacts, and bad results but if Voltage regulator overheats it is hard lock without warning.
Your right.....My power draw is 980-1020watts
Also, i am using data 2.5" HD. these use minimum wattage.
I will try to disable everything on MOB that i do not use.
How do I down clock the mem to 300? I am using afterburner and only can bring it down to 500.
Do you think by adding extenders with molex, I can over clock it some more? these cards should be able to handle OC at 900. (all three together) right?
Also, how much did you increase the voltage to?
thanks