CGMiner freezing on anything above intensity 16

Question

I have 2 x Sapphire 7950 Boost cards running on Windows. I can only get them running stable on intensity 16 using CGMiner. Anything above that and the whole system freezes up (screen stays on but everything else is unresponsive).

Previously I had them on linux running BAMT, and I could get them running fine on intensity 18/19 for longer.

So I'm positive the cards should be able to handle greater than intensity 16, and I have two more PC's with just a single card in running around 600 KH/s, so I know they can.

What could be causing the system to freeze? Is it the cards or could it be drivers etc? Theyr'e only clocked at 1000/1250, with 24768 for thread-concurrency. Nothing over the top, and settings which are fine on the two single card PC's.

Here's my config file:

"kernel"            : "scrypt",
"scrypt"            : true,
"no-submit-stale"   : true,
"temp-cutoff"       : "85,85",
"temp-overheat"     : "80,80",
"temp-target"       : "70,70",
"auto-fan"          : true,

"api-listen"        : true,
"api-port"          : "4028,4028",

"intensity"         : "16,16",
"vectors"           : "1,1",
"worksize"          : "256,256",

"lookup-gap"        : "2,2",
"thread-concurrency": "24768,24768",
"gpu-engine"        : "1000,1000",
"gpu-fan"           : "0-90,0-90",
"gpu-memclock"      : "1250,1250",
"gpu-memdiff"       : "0,0",
"gpu-powertune"     : "0,0",
"gpu-vddc"          : "0.000,0.000",

"expiry"            : "30",
"gpu-dyninterval"   : "7",
"gpu-thread"        : "1",
"sharethreads"      : "32",
"log"               : "5",
"queue"             : "1",
"retry-pause"       : "5",
"scan-time"         : "30",
"temp-hysteresis"   : "3",
"shares"            : "0",

"kernel-path" : "/usr/local/bin"

Answer 1

I eventually figured out this problem, and it was solved by lowering the voltage on the cards to 1100 or 1150.

Stock Sapphire 7950 boost cards are volted at 1250, and when running both cards concurrently it was making the system unstable and thus it would crash. Even so, I would have expected a Corsair CX750 to still be able to handle them both, but it seems not.

Lowering the voltage through Sapphire Trixx makes the whole rig stable, and I can now run at 18/19 intensity without any problems. Heck I might even try 20 soon ;)

Hope this helps anybody out in the same situation.

Answer 2

Your question "fixed" my problem. I have a computer with 4 X Saphire HD 7950 and I am dealing with the same problem. I think it's power related issue but I have a 1300 gold rated unit... I used to just have it sit at 13 intensity while I figured out this but now I can sit it at 16! Anyways I don't want Munch to get angry at me so I'll add a bounty on the "if" someone could resolve this $5 of BTC will be heading their way.