# Overclock AMD Radeon HD 6950



## andrea1192 (Jul 1, 2011)

Hi, I have an unlocked Sapphire 6950 that I would like to overclock to 6970's frequencies (from 800/1250 to 880/1375).

After some tests with GPUTool and Furmark (the card performed without problems, no artifacts and the temperatures were around 60-70°C) i tried Crysis 2 and appeared a BSoD.

Then I did some other tests with:

- everything at default: no problems
- GPU @ 840, memory @ default: the first time I tried the framerate fell suddenly (to 1fps), then the game ran normally without other problems
- GPU @ 880, memory @ default: the first time I tried appeared a BSoD
- GPU @ 880, memory @ default and the original bios: another BSoD

Now everything is at default (also the bios):







What can I do? My card doesn't support the 6970's frequencies? Could it be a power problem? 

Thanks,
Andrea.


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## DiogoCDS19 (Jul 1, 2011)

You should fill your system specs so we can see what you got and find out what is the problem.


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## andrea1192 (Jul 1, 2011)

Asus P5Q Pro, Core 2 Duo E8400 (@default, 3Ghz), 4GB of DDR2 RAM, Corsair TX650W power supply.


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## DiogoCDS19 (Jul 1, 2011)

Do you remember whats the error message in the BSOD, also, what drivers are you using ?


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## arroyo (Jul 1, 2011)

@ andrea1192

You must bump GPU voltage from 1.1V to 1.175V. Your card does not want to work with 880MHz clock, because HD6970 uses 1.175V for this clock to be stable. Mine HD6950@HD6970 does the same.


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## andrea1192 (Jul 1, 2011)

@ DiogoCDS19

I don't remember the message of BSoDs, they disappear too quickly... however I'm using the Catalyst 11.6 drivers.

@ arroyo

Is that voltage safe for a 24/7 overclock? The two 6-pin connectors of the 6950 are enough? Have you increased the value of "power control settings" in the CCC?


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## arroyo (Jul 1, 2011)

It is safe for 24/7 as long you do not overclock memory on HD6950. Two 6-pin connectors will be enough. Leave "power control settings" at default level in CCC. Change voltage via MSI Afterburner (safe way) or by RBE (hard way, only if your card is reference model).


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## PopcornMachine (Jul 1, 2011)

arroyo said:


> @ andrea1192
> 
> You must bump GPU voltage from 1.1V to 1.175V. Your card does not want to work with 880MHz clock, because HD6970 uses 1.175V for this clock to be stable. Mine HD6950@HD6970 does the same.



I also have to set voltage to 1.175, and am then able to run mine at 900/1400.

Other overclocks with less voltage may work in 3DMark11, but will crash in Crysis 2.

Although it seems high to me, it appears safe for daily usage. I set the voltage and overclock using MSI Afterburner.


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## andrea1192 (Jul 1, 2011)

Ok, I'll try again Crysis 2 at 880/1250 with the 1.175 voltage. The overclocking of the memory brings many advantages? Why is less safe in 24/7 than the overclocking of the GPU?

EDIT: I'm doing my tests with Sapphire Trixx because I have a Sapphire-branded card...

EDIT2: Seems to be stable  The GPU temperature is around 70°C, but i see in GPU-Z that the "Vreg temperature" reaches 50°C. What is it?


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## PopcornMachine (Jul 1, 2011)

andrea1192 said:


> Ok, I'll try again Crysis 2 at 880/1250 with the 1.175 voltage. The overclocking of the memory brings many advantages? Why is less safe in 24/7 than the overclocking of the GPU?
> 
> EDIT: I'm doing my tests with Sapphire Trixx because I have a Sapphire-branded card...
> 
> EDIT2: Seems to be stable  The GPU temperature is around 70°C, but i see in GPU-Z that the "Vreg temperature" reaches 50°C. What is it?



My understanding is that Vreg is the voltage regulation module.  50C is not a problem for any component.

And I am unaware of any problem with overclock of the ram.  It does help performance.  Like I said, mine is at 1400MHz and is working fine.


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## LordJummy (Jul 1, 2011)

Just a quick note: in my personal experience with now four (4) 6950 2GB's that putting the memory over 1375MHz makes almost zero difference in performance gains. The core clock is by far the most important thing you can increase to gain real performance.

My main 6950 is a modded 6950 bios with unlocked shaders, voltage unlocked, etc. 

Gaming clocks: 1000Mhz core / 1375Mhz memory
Benchmarking & Tests: 1075Mhz core / 1400Mhz memory

I have tested it at 1075Mhz core with 1250, 1300, 1350, 1375, 1400, 1425, 1450, and 1500 Mhz memory and the performance difference is almost nill.

That's just my experience though with my cards. Try it out your self 

Be warned though, once I go too far over 1500Mhz memory these things tend to die. I've had a couple of them artifact permanently after benching at 1550Mhz+


*Oh, and all of mine are reference 6950 2GB's. So if you have better cooling for the memory you could possibly get it higher, but in my opinion there's no point in going over 1400Mhz


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## andrea1192 (Jul 2, 2011)

Thank you for your replies, now the card is stable also at 6970's frequencies.

But I'd like to know more about the "power control settings" in CCC, because I read it's important to set this parameter to prevent damage... Have you ever used it?

I'm a fearful man


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## Leito360 (Jul 7, 2011)

arroyo said:


> It is safe for 24/7 as long you do not overclock memory on HD6950.



I own 2 6950 Twin Frozr III. I was unable to unlock any of them, but I was thinking to OC to reach frequencies of a 6970.
So far I played DNF, FEAR3 and BC2. With the first two there was no problem, but with BC2 the system froze. It could be because the OC?
I didn't touch the voltage. Should I give them 1.175?
Why isn't safe to OC the memories?

BTW: I'm using a XFX BE 850W PSU... Will be enough to support the 1.175 on each card?


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## ChristTheGreat (Jul 15, 2011)

XFX PSU (Black Edition and Pro series) are Seasonic M12D if I am right. It will be enought for HD6950 overclocked and CPU overclocked..


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## Pestilence (Jul 15, 2011)

My 6870 went to 1.1Ghz core. The 6950's should easily hit 1Ghz


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## cadaveca (Jul 15, 2011)

andrea1192 said:


> Thank you for your replies, now the card is stable also at 6970's frequencies.
> 
> But I'd like to know more about the "power control settings" in CCC, because I read it's important to set this parameter to prevent damage... Have you ever used it?
> 
> I'm a fearful man



The power control settings are usualyl fine @ "0" for most games. 

You want to see it at work? Open up GPU-Z, then fire up Furmark. Watch Core clocks in GPU-Z. See them bouncing around? That's the power control kicking in.


My 6950's behave as your does. However, I recently put a waterblock over the GPU of one of them. Now 900 MHz is 100% stable, where on the stock cooler it wasn't, without a votlage increase.

Unlike Lord Jummy above, I did find that ram speed made a signifigant difference in perforamnce. 1250 MHz mem is for 1408 shaders @ 800 MHz. 1375 MHz mem for 1536 shaders @ 880 MHz. That 125 MHz seems to matter a bit, keeping the GPU fast and efficient.

However, like Lord Jummy, much more didn't make much difference.



Pestilence said:


> My 6870 went to 1.1Ghz core. The 6950's should easily hit 1Ghz




Sure, but no. the silicon is capable, for sure, but the core design is much different, so just because your 6870 does it, doesn't mean a 69xx will. The larger die size is harder to cool, and heat buildup will prevent mayn cards from hitting 1000 MHz, unless on water or better cooling.


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## Pestilence (Jul 15, 2011)

cadaveca said:


> Sure, but no. the silicon is capable, for sure, but the core design is much different, so just because your 6870 does it, doesn't mean a 69xx will. The larger die size is harder to cool, and heat buildup will prevent mayn cards from hitting 1000 MHz, unless on water or better cooling.



So glad i didn't buy a 6970 like i had planned then.


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