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Overclocking HD 6950

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blade52x

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Sep 9, 2006
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I recently got a HD 6950 2gb Twin Frozr II, which has this giant custom cooler on it, so I figured, why not? I didn't overclock my previous crossfired 6850s because they ran too hot (my p182 isn't ideal for cooling anymore).

1) FurMark
I managed to unlock the extra shaders, and then I decided to use MSI Afterburner to increase the clocks. The stock clocks of this card are 800/1250. I pushed them up to 875/1350, and I ran FurMark full-screen burn-in for 30 minutes without any crashes. However, during general desktop use, my screen just froze. This has happened twice now, but does not happen at stock clocks, so it seems my overclock is unstable. I can probably push the VCore from 1.1V (stock hd 6950) to 1.175V (stock hd 6970), but that's not the point I'm trying to get at here. Basically, FurMark failed to tell me the overclock was unstable... it simply does not crash. I've had to push the core clock to 925+ before I started getting system locks using FurMark. I think this is because of the clocks going up/down during FurMark (I've read this is common) and that his has something to do with the power control setting. Is there anything I can use as a good test for stability?


2) CCC Power Control settings
So I've read up on what this is, but to hell with AMD drivers, because everything keeps defaulting on me when I change things around in MSI Afterburner. Basically, when I try to set +10% power control, and then change the clocks in Afterburner, when I reload CCC, all of my clocks and power control settings reset. So is there any way to set power control and higher clocks than CCC will allow for? if I set +10% in CCC, and go change clocks in MSI Afterburner, but then never open CCC again, does the +10% power control setting stick?

That's about it for now. Thanks in advance.
 
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Some interesting tidbits here. I'll give you advice from my own experiences.

First, congrats on the shaders. 1536 is definitely an awesome freebee with the 6950s. Also having such a good cooler to tame them is a plus also.

Furmark/Kombuster and OCCT are the most demanding and should be an accurate stability test if done right. Other factors and system bugs cam come into play here.



The first thing I would do is up the voltage to 1.175 and see how far you can go in furmark without losing stability. Use the extreme preset that gives you the ugly scary disclaimer message, that makes it sound like your rig will explode. Make sure to set everything to it's highest value, including AA and set DX11 etc... Also use the max resolution of your display/s

Kombuster is the same thing as furmark only it's available by msi to complement afterburner. That's what the K launches on the afterburner screen (if kombuster is installed)

OCCT is equally demanding and stands for over clock checking tool. Helpful tool to check for stability.

**************

On a separate note, What I recommend you do is to set afterburner to defaults by clicking reset. Then apply. Close afterburner with the X and then open CCC. Enable AMD overdrive and set the +20 powertune for your card/s and apply. Don't touch anything else there. Close CCC and then launch afterburner via the .exe file. Set you clocks or load your saved preset e.g. (click on 1 or whatever # assigned) hit apply to apply your clock etc..

**************

I have found that if you enable amd overdrive while afterburner is already administering clocks and tweaks that it is overriding the amd driver to do and you then enable amd overdrive, make any changes and apply that you create a conflict. You may even notice that since the clock in AMD overdrive are default that your clocks change to default and then the next minute they change back to what afterburner has set, almost as if the 2 programs are playing tug of war.

Follow the steps between the asterisks and you should be fine. That's how I finally tamed that nuisance
 
Ive had the same problems with Furmark/Kombuster and my Twin Frozr II's with unlocked shaders. Though mine doesn't lockup during general desktop use, but will in game. I can run stable at 880/1375 and 1.181 voltage (Afterburner doesnt like 1.175 and my card)

I solved the other issue of CCC reseting by doing a registry hack and allowing a higher OC in CCC.

Link for hack is here.
 
Unlocking the shaders limits the maximum overclock you can achieve. You may want to check if you get better performance with 6950 shader count + possibly higher overclock.
 
Furmark/Kombuster has not been a good stability tester for me the newer cards like my 6950 or GTX 580. I have had better luck looping the Heaven demo, running the Metro2033 benchmark 15-20 times, running 3dMark11 and of course playing a gpu demanding game like Crysis 2 for 20+ minutes. I can run Furmark/Kombuster with substantially higher clocks with no stability issues than I can those other methods.

I personally like the Sapphire Trixx for overclocking my AMD cards and have had good luck with it.
 
Thanks for the tips. The registry hack worked nicely. I think flashing to a 6970 upped my Vcore, as it's always at 1.172V as reported by GPU-Z. The only thing is that is not drop down when idle, but whatever. I'm now running 900/1375 through CCC, which is nice because now I don't have to worry about my power control resetting. :D
 
Is AMD making their new drivers harder to O/C with or something? I'm running a reference 6950 with unlocked shaders. I recently formatted my comp and my old method of using Asus smartdoctor to up the CCC limits wouldn't work right. As soon as the comp rebooted the CCC limits were back to normal (840/1325 or whatever). I ended up having to use that registry hack, but even then I don't have voltage control in Afterburner now (even after checking the box for voltage control). It's not THAT important as the bios I'm using sets voltage to 1.175, but still. My initial 6950 o/c procedure seems to just not work right anymore.

I thought I'd pose the question, any ideas?
 
What happens when you try and change voltage in afterburner? Afterburner was super finicky for me, if I set a voltage it didn't like it went back to default. It didn't like 1.175, but likes 1.181......
 
apehangers said:
What happens when you try and change voltage in afterburner? Afterburner was super finicky for me, if I set a voltage it didn't like it went back to default. It didn't like 1.175, but likes 1.181......
Click to expand...

Well it appears to be fixed now. Man I love it when things fix themselves :p
 
good thread, I always found the interaction between CCC and afterburner maddening also

does that registry hack do the same thing as smartdoctor?
 
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