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Overclock intel i5-2500K

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June 24, 2011 8:21:32 AM

Hi, I want to ask for an advice on how to overclock intel core i5-2500k.

I am a newbie in this field. My MB is ASRock z68-Pro3-m. I just want to do some mild overclock on my intel since I don't have any after market HSF. I plan to overclock to 3.7 GHz. The problem is the core voltage. There are 2 choices (instead of auto) which are Offset and Fixed voltage. Which one is better for overclocking? Offset or fixed?

I tried both method, but gave me different results.

Fixed Vcore=1.175V
Prime95 for 4 hours without any problems. Benchmarking on some variety of games with no problem.

Offset Vcore= -0.005V
Prime95 never last for more than 15 minutes and BSOD
Benchmarking on games never succeed, always auto restarting my computer.

I read in some forum said that offset -0.005V means= default Vcore-0.005V
default Vcore for i5-2500K is 1.300V so after substracted by the offset voltage is equal to 1.295V which is higher than 1.175V (in fixed mode). However, why did 1.295V always gave me BSOD? In my understanding on overclocking, higher voltage means more stability, but this is not so likely.

Is this MB (Mobo) problem? or CPU Problem?
Please advice me. Thanks in advance. :-)

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a c 107 V Motherboard
a b K Overclocking
June 24, 2011 2:20:58 PM
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Default Vcore for Sandy Bridge CPUs is 1.2v, not 1.3v

And Offset isn't "default voltage plus or minus the offset", it's "some mainboard-specific value plus or minus the offset."

The mainboard-specific value is likely well below the default Vcore, which is why it is giving errors during testing. The best way to find out what the voltage is, is to go into the hardware monitoring section of the BIOS and see what the value is. Then change the offset value and save and exit, and go back into the hardware monitoring section again to see how it changed.

You shouldn't use fixed voltage, as that keeps the same voltage even when the CPU is down-clocked to 1.6GHz for idle mode. Offset mode allows you to set the peak load voltage while still allowing the voltage to go lower when the CPU idles.
June 24, 2011 4:24:31 PM

Leaps-from-Shadows said:
Default Vcore for Sandy Bridge CPUs is 1.2v, not 1.3v

And Offset isn't "default voltage plus or minus the offset", it's "some mainboard-specific value plus or minus the offset."

The mainboard-specific value is likely well below the default Vcore, which is why it is giving errors during testing. The best way to find out what the voltage is, is to go into the hardware monitoring section of the BIOS and see what the value is. Then change the offset value and save and exit, and go back into the hardware monitoring section again to see how it changed.

You shouldn't use fixed voltage, as that keeps the same voltage even when the CPU is down-clocked to 1.6GHz for idle mode. Offset mode allows you to set the peak load voltage while still allowing the voltage to go lower when the CPU idles.



Hi Leaps-from-Shadows, thanks for the info on default Vcore. I thought it was 1.3v since the default Vcore on my Mobo is 1.3v

I just did like you said. When I select fixed 1.175v the Vcore is stable on 1.175v, there was no voltage throttling at all. Then I changed to offset -0.005v, the maximum voltage according to the BIOS is 1.295v but it throttled down when idle.

The problem now is even with offset -0.005v, I kept experiencing BSOD or automatically restart when running Prime95 blend mode, but the problem was gone when I use fixed 1.175v.

Any Idea of what should I do next?
Thanks in advance.
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a c 107 V Motherboard
a b K Overclocking
June 24, 2011 11:14:11 PM

Maybe it's because you're giving it too much voltage? Change the offset to -0.120v then save and exit and see what the voltage is in the BIOS. It should be near 1.175v like you had it in fixed mode. Then test it with Prime95 again.
June 25, 2011 3:15:44 PM

still no luck :-(. It always failed prime95 and benchmarking test using offset voltage :'( .
a c 107 V Motherboard
a b K Overclocking
June 25, 2011 3:27:16 PM

That's weird -- it should work with no problems. Evidently offset mode isn't perfected yet on that board, or your CPU just doesn't like it.

What happens when you leave the voltage at Auto? Unless you get failures, that mode should be better than fixed mode.
June 25, 2011 4:13:19 PM

tried auto mode too and it failed. My system is fine without any OC.
I've searched some forums and found out that there are 2 other people who were experiencing the same problem as I do and guess what? Both of them are using ASRock Mobo (which is also my Mobo) T_T. I think I will try to RMA this Mobo and hope that they are willing to replace it.
June 25, 2011 7:41:08 PM

Hi Leaps-from-Shadows,
I think I find the culprit behind all of this mess.
At first, I tried to disable LLC by setting Vdrop to 0V but still not working.
Then I disable Turbo, and still not working.
Then I disable All C-states, and it worked. Every thing runs normally.

Now, I have another question, which one is better: using fixed Vcore but enable all the C-states, or Using offset Vcore but disable all the C-states?
June 26, 2011 6:41:40 PM

Best answer selected by hasappra.
a c 107 V Motherboard
a b K Overclocking
June 26, 2011 9:26:08 PM

The C-States are basically the power-saving features of the CPU, so that might make the choice for you if you're concerned with that kind of thing. I guess if I had that choice I'd use Offset mode and disable the C-States.
June 28, 2011 4:55:59 PM

Leaps-from-Shadows said:
The C-States are basically the power-saving features of the CPU, so that might make the choice for you if you're concerned with that kind of thing. I guess if I had that choice I'd use Offset mode and disable the C-States.


Thanks a lot for all your help. :-)
!