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Author Topic: Why won't my 6950 overclock past ~900 mhz core?  (Read 1512 times)
gregr507
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June 21, 2011, 09:01:59 PM
 #1

Wish I could post this in the section it belongs in since I'm not really a newbie but oh well...

I just got a sapphire 6950 1gb version, and have been trying to overclock it (for bitcoin mining at the moment). I've tried using different programs (CCC, afterburner, trixx) to overclock, and can get the core up to 900, but once I go much past this the card immediately throttles down. I've tried increasing the power control in CCC, but it doesn't seem to do anything. Is there any way around this?? Thanks in advance
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Bitslizer
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June 21, 2011, 09:17:59 PM
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what temp...? does the card throttle down only when you are mining? or immediately after you try to set the >900mhz core?
gregr507
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June 21, 2011, 09:23:13 PM
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The temps go up to a little over 80 degrees C. Fairly hot, but I don't think that's hot enough to automatically throttle down? It's weird, I'm at 880 core right now and getting just under 350 Mhash/s. But if I bump it up to 910 or 920 it throttles down and I'm at 200-something. This is while I'm mining.
Bitslizer
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June 21, 2011, 09:26:01 PM
 #4

try pointing more fans at the GPU, set the GPU fan to manual @ 100%, and if the case is closed, open it up and see if that help.  Then at least you would know if its overheating problem or not
gregr507
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June 21, 2011, 09:27:11 PM
 #5

Yeah I did try setting that fan at 100% manually before doing this, and it still did the same thing. I've tried adjusting the power control in CCC but it doesn't seem to do anything
a1phanumrc
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June 21, 2011, 09:29:20 PM
 #6

Have you tried unlocking the shaders and flashing the 6970 BIOS on?  I'm having great success on mine, both clocked to 920 and stable.

http://www.techpowerup.com/articles/overclocking/vidcard/159

BC tips: BA1phaSEpCN7jiSS33SSWXf3Bs1rP9SKir
gregr507
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June 21, 2011, 09:31:46 PM
 #7

Yep I tried unlocking the shaders and flashing the bios, but I have a non-reference 6950, and it's the 1gb model. And the flashing/unlocking on those cards doesn't seem to always work, and it hasn't for me so far
a1phanumrc
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June 21, 2011, 09:33:15 PM
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I don't remember where exactly, but somewhere on this forum someone mentioned successfully doing so on the 1gb model, but you can't use the GUI - must be done via command line.

Just a thought.

BC tips: BA1phaSEpCN7jiSS33SSWXf3Bs1rP9SKir
gregr507
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June 21, 2011, 09:35:31 PM
 #9

Yeah I saw that, I may give that a shot but I feel like I've been wasting time trying to squeeze performance out of this card while I should just leave it up mining lol. Also the bios that I would flash to wouldn't be the 6970 bios, it'd be a modified 6950 with the shaders unlocked. So I'm worried I may still have the throttling problem if I try to overclock it after I unlock the shaders (if that's even possible on this card)
genkido
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June 21, 2011, 10:59:13 PM
 #10

I'm running 2 6950's at 925Mhz, no overvoltage, using Afterburner. Going past the 925 marks creates great inestability for the driver (most likely insufficient power) and crashes. Over 975 means BSOD. Got about 40MHs extra. Shaders are unlocked by the way.
gregr507
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June 21, 2011, 11:23:24 PM
 #11

I'm running 2 6950's at 925Mhz, no overvoltage, using Afterburner. Going past the 925 marks creates great inestability for the driver (most likely insufficient power) and crashes. Over 975 means BSOD. Got about 40MHs extra. Shaders are unlocked by the way.

What happens when you start pushing it up past 925? Does it downclock? Because once I get to 900ish it starts wavering back and forth between 880 or so and 900. If I push it higher it just downclocks even more. Do you have a 2gb or 1gb card? Also what kind of power supply? I have a 600W psu, and nothing is overclocked besides the 6950. Also what version of CCC are you using? Sorry for all the questions lol
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