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Prime95 FATAL ERROR Rounding Question

post #1 of 11
3/26/08 at 12:03am
Thread Starter 
I've been experimenting with different FSB and multi settings and found that the best benchmark score in 3DMark06 so far is when I set FSB to 420MHz, multi 9, although I haven't yet gone over 430MHz. The highest I have had my CPU running is with 390MHz FSB, multi 10.

So I decided it was time to check stability at different settings. And I get the message below; at 430MHz FSB this occurs after 6 minutes and at 420MHz after 28 minutes and its always on core 3.

FATAL ERROR: Rounding was 0.5, expected less than 0.4 Hardware failure detected, consult stress .txt file. Etc, etc......

When running Prime96 my CPU is within Intels recommended thermal specification but there is a difference in core temps, these seem to range as follows:

CPU: between 50 and 62
Core1:between 44 and 56
Core2:between 44 and 56
Core3:between 50 and 60
Core4:between 50 and 60

My Vcore is set at 1.3625v, memory to CPU ratio is 1:1.

I haven't had time yet but I'm going to run Prime96 at stock setting to see what results I get.

Have I got a CPU with a bad core or is this quite common when overclocking, have I just got to find the sweet spot?
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post #2 of 11
3/26/08 at 1:18am
You could try to go over 430 on your FSB.
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post #3 of 11
3/26/08 at 3:36am
when you get rounding errors it an unstable o/c. your chip is probably fine, you need to bump up the vcore a notch or 2. i'm not sure what the max volts are for that QX9650, look it up, and make sure you dont go over it, you'll be fine.
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post #4 of 11
3/26/08 at 3:37am
don't be alarmed. It just means your cpu isn't stable.

Try other settings.
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post #5 of 11
3/26/08 at 2:43pm
Yup, bump vcore. Make sure RAM is getting enough voltage, along with north bridge to try things as well. Also, if you run the small FFT succesfully, it leans towards the cpu being stable. If you then failed the blend test, it suggests RAM and/or northbridge are involved.
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post #6 of 11
3/26/08 at 2:54pm
Quote:
Originally Posted by Abilor View Post
Yup, bump vcore. Make sure RAM is getting enough voltage, along with north bridge to try things as well. Also, if you run the small FFT succesfully, it leans towards the cpu being stable. If you then failed the blend test, it suggests RAM and/or northbridge are involved.
^What he said. While OC'ing I found out that 95% of the time it was my RAM settings causing the instability.
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post #7 of 11
3/26/08 at 3:09pm
rounding error means you need more vcore
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post #8 of 11
3/26/08 at 8:56pm
It also could be the ram voltage or the northbridge voltage. It usually helps to increase the NB to 1.4v or 1.55v when o/c'ing. Also try 2.1v ram voltage. You can always drop these back down if it turns out the cpu voltage that is too low. The maximum cpu voltage is 1.3625v on these, although you could set the bios at 1.4v and you may see 1.36v in reality (CPU-Z) with vDrop.
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post #9 of 11
3/26/08 at 11:55pm
Thread Starter 
Thanks everyone for the feedback, there are some useful tips here.

Last night I experimented with different Vcore settings; I started at 1.3625v went into windows and loaded cpuz and noticed that the mobo undervolts a bit. So went back to BIOS and raised the voltage a couple of settings and repeated this process until I got to a point where cpuz was reporting 1.362v.

I notice that this board seems to overvolt the ram voltage a bit so I set my RAM voltage at 2.1v and went through the same process until Everest was reporting DIMM volts at 2.1v.

My NB and SB voltages are set in BIOS at auto, Everest reports that these are 1.63v and 1.07v.

I haven't run Prime95 for a great length of time yet as I went out last night and I don't like the idea of leaving the PC running without monitoring it. However, I did manage Prime95 for 1 hour without any errors.

The cpu core temps seem a bit odd though, Everest reports that cores 1 and 2 are always runing at least 10 degs C lower than cores 3 and 4.

Thanks again everyone for the good feedback, I'm gonna try running Prime95 for 8 hours and I'll report back in a couple of weeks as I'm off on holiday to do a spot of scuba diving.
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post #10 of 11
3/27/08 at 11:42pm
Thread Starter 
I managed to get a bit of Prime95 testing in last night while packing up to go on my scuba trip and managed just over 4 hours without any errors so things are looking better.

+reps for the advice.

Sniffs .............
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