I can't OC my Saphire 5850 Xtreme cards GPUs higher than 850-875MHz

[Unclegogi]

Hello, guys!

I have some mining hardware, including 8 x 5850, 1 x 5770 and 1 x 5750.

There are some people, who use same cards with GPU OC up to 950-975MHz with stock voltage (for example in this topic: https://bitcointalk.org/index.php?topic=34434.20 ).

I have six Saphire 5850 Xtreme cards, max stable OC clocks are 875, 875, 850, 850, 850 and 800MHz. Two reference 5850s (powercolor and xfx) work stable with GPU@890MHz.
All the cards can't work at 900MHz or higher, I can set up core clock at 950MHz for example, but the PC freezes after i start phoenix and only reboot helps. If I set up 900Mhz clock, it may work some minutes, and then the driver throws an error and switches to default clocks.

I'm using windows 7 x64 on all my mining PCs.
I have tried different hardware combinations, different PSUs, no changes.
Should I try another OS (Win XP, Linux) for better OC?

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[Kermee]

Which cards on which PSU's are they on? That's the first step...

Cheers,
Kermee

[Unclegogi]

FSP SPI-600 (600Wt) for 2 x 5850 cards.
FSP SPI-600 (600Wt) for 2 x 5850 cards.
Delta GPS-550AB-A(550Wt) for 5850+5770+5750 cards.
Thermaltake Litepower 450 (450Wt) for one 5850.
etc

I have tried to use only one 5850 with FSP SPI-600, and I see no changes.
Also I have switched the cards, and no changes in their max stable clocks.

I have tried to run 3 x 5850 on FSP SPI-600, it worked with gpu underclock (600MHz), 600Wt PSU can't run 3 x 5850 on stock clocks on with OC for sure, but it is more than enough for 2 x 5850.

PS 5750 work well @ 850/300 and 5770 work @ 925/300, the question is - if it is possible to make 5850s somehow work with better clocks, than 850/300 with stock voltage...

[Callius]

It's possible you're just unlucky and have got cards that won't run that far above the stated spec. Your problem might be keeping them at stock voltages but I assume you're doing this because you've tested with raising it and the Power supplys won't be sufficent to support that?

Have you checked that your temperatures are ok? I also run 3 sapphire extreme HD 5850s and the two which run in the same rig tend to heat up significantly more than the solo one, to the point that 800Mhz is the best I can get out of the core clock.

[Unclegogi]

Callius, it's quite warm in the room with mining PCs, and temperatures on GPUs are 75-80C while mining.
Increasing voltage increases temperatures drammatically, so I haven't even tried to increase voltage on theese Saphire cards.

[Hotdog453]

Personally, I wouldn't worry about the temperature that much. 80-85-90-95 just doesn't bother me that much.

I'm personally running a mix of 5830s and 5850s, and they're all running at 85+ degrees, all overvolted. The cards are 'designed' to work that hot; it looks terrifying, but I haven't had any issues thus far.

FWIW, my 5850s, over volted, are running at anywhere from 775mhz to 850mhz; it's a crap shoot. Some will go farther, some simply won't. I'm striving for 100% stability though, obviously.

[jh1523]

Get some decent coolers for the cards - obviously the stock ones can't do too good a job. My 5850 is a MSI twin-frozer, runs nice and cool at 65 degrees, stock voltage, core clock to 930MHz, very stable, getting about 380Mhash/s out of it. In tests that I've done it worked up to 960MHz stable but hotter, and I decided to not push it to the limit.