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Hi, i have a rig of x5 5850, custom case, so all the GPU are realy separated from each other and all with risers....To power is suplied by 2 x CL SP 700w, and the temperature never never go more than 52c. The fact is that i cant overclok the rig more than 850/300 so im onl getting 340mhs wich is realy bad for a 5850.
When i try to go more than 850 it fails. The OS (BAMT) stops responding so i have to reboot manualy the rig. Dont know wich the problem could be.

Im using:
OS: BAMT 0.4b
All the 5850 are Saphire Xtreme.
Driver 11.6.
Miner Phoenix.

What OS are you using? Which brand/model 5850's are you using?

If your using windows 7 I recently built a 5x5850(sapphire) rig and the screen would freeze if I pushed it too far or tried downgrading the memory to below 500 mhz. Upgrading to 11.7 drivers and using trixx in staid of afterburner fixed all my problems.

What software are you using to OC?

Im using:
OS: BAMT 0.4b
All the 5850 are Saphire Xtreme.
Driver 11.6.
Miner Phoenix.

Some 5850 don't like having their memclocks downclocked too much.  Took me a while to figure this out, since I was used to setting memclock on my 5830s to 325.  My 5850s don't like anything less than 550.

I have the same problem. But with 865mhz+ on coreclock, i got driver stop and reboot. With Sapphire Extreme and XFX, both 5850.

Would like to increase coreclock, without changing the voltage.

 :-\

Give the details of that rig so we can discard posible erros.

It's also possible that you just got a bum card.  Do you have another box you could put it in as a test?  That would rule out a bunch of possible issues.

I'm also using BAMT 0.4b on a 5x 5850 open rig with a mix of card brands. I had one card that could not sustain anything over 875/300 and it would bring down the whole rig after a couple of hours. However, one 5850 with an aftermarket Sycthe SCVSG-1000 cooler is doing a stable 920/300 and might do a little more. BAMT is excellent for troubleshooting single cards, just set each GPUx setting in bamt.conf to disable=1 except for the card you are testing. When you find that specific card's OC limit, back off 5 or 10 MH/z. Then go to the next card, ect. until you have all five set to a stable OC. Works great. Stability rules over max OC IMO.

Try using TRIXX, it might solve your problem.

one of my gpgpu open rigs has a bunch of sapphire extreme running bamt, overclocked to 950/300 on stock voltage, but that is no guarantee that any of your chips should reach this as well.

If your system hardlocks to the point where you are unable to nothing when you try and overclock any of the cards past 850 I would expect PSU to be issue.
Are you overclocking using bamt.conf or do you do it manually? if manually, which program?

Keep an eye on dmesg for errors.

Do you have a single core CPU?

I have 3x 5850 (2 Xfx, 1 Sapphire extreme) on a motherboard (ecs a890gxm-a), and core/mem configured (865/320) with AMD Gpu Clock Tool, and fan set manual in 60%, temp are in 65-70°.

But if I try set more 5mhz to coreclock (870), after 5-10min i got blue screen.  >:(

OS: Windows 7 Ultimate
Driver: 11.7
Voltage: stock

What you say? =/