Strange i5 750 Overclocking

liquidex

liquidex

liquidex

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15 Dec 2008
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Hey all,

Hope someone can help me with these characteristics but I am baffled.

Have been running my i5 750 with the specs in my sig at 4ghz (20x200) with 20 runs Linx stable (with the newest linpack) and a couple hours of prime. This is normally good enough for me as I do not do anything that stressful and I haven't had any problems since using this overclock a few months ago.

Since last week I have been trying to get it stable at 3.8ghz as it was quite warm. Did get it stable but when using the Dynamic Vid feature on my Gigabyte board however, it enters an infinite loop when exiting sleep and I have to clear the cmos to get it to boot. So I tried different multipliers to see if it behaved any better, as I heard that these chips prefer odd ones, and I cannot even get to the bios screen without having to recover the bios. Any ideas on what could be causing this behaviour would be appreciated, as I remember when I did try 3.8ghz when I just got the chip with the combinations listed below they were fine.

4ghz (21x191) Vcore: 1.33V, Qpi/Vtt: 1.26V, PCH: 1.1V
Stable using the method above

4ghz (20x200) Vcore: 1.33V, Qpi/Vtt: 1.26V, PCH: 1.1V
Stable using the method above

3.8ghz (21x181) Vcore: 1.26V - 1.33V, Qpi/Vtt: 1.26V, PCH: 1.1V
Cannot get to bios

3.8ghz (20x190) Vcore: 1.26V - 1.33V, Qpi/Vtt: 1.26V, PCH: 1.1V
Cannot get to bios

3.8ghz (19x200) Vcore: 1.26V, Qpi/Vtt: 1.24V, PCH: 1.1V
Using Dynamic Vid stable with the method above but goes into an infinite loop when exiting sleep

I know I could just run 19x200 without Dynamic Vid as the Vid probably drops too low to get the chip to boot but I would like to know if possible why my chip behaves as it does.

Thanks
 
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What multiplier are you using for the RAM and what speed is your RAM rated at?

Every time you increase the Base Clock you're increasing the speed of the RAM. Push it too far and your RAM won't be able to cope.

Edit:

That's probably irrelevant.

I should read the whole post :o
 
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ok well first: Your Vtt is fairly high, if your running this 24/7 Intel says max 1.155V.

do you have C1E enabled in bios, if you do this lowers the voltage and the clock and could cause instability in sleep mode (maybe this in combination with your Dynamic voltage is messing with you?). I'm not 100% on why it would then go into an "infinite loop" but its worth turning this of if its on.

http://www.hardwaresecrets.com/article/611

hope this helps
 
I thought the Intel max from the datasheet had been changed to 1.4V?

From looking at the bit-tech guide and some overclocks on here I thought 1.26V was quite conservative and would need to pump more vcore through the chip to compensate if vtt was lowered.

Have disabled the C3/C6 states but going to tinker with C1E and report back. Thanks :)
 
you are somewhat correct, the absolute maximum has been changed from 1.21 to 1.4, but to quote Intel:

"If a device is returned to conditions within functional operation limits after having been subjected to conditions outside these limits (but within the absolute maximum and minimum ratings) the device may be functional, but with its lifetime degraded depending on exposure to conditions exceeding the functional operation condition limits."

http://download.intel.com/design/processor/datashts/322164.pdf

section 7.8 paragraph 1

take it with a pinch of salt, most people overclocking 1156 still think that the max is 1.21... Just letting you know, in case your someone who worries about these things like me :)
 
Thanks have lowered it to 1.22V and with a quick and dirty linx test its ok.

Using 3.8ghz (19x200) atm and it seems fine, but again other combinations still cannot even get to the bios screen before restarting. Hmmmm.

Might just put it back to 4ghz and leave it.
 
Quick update.

Got 3.8ghz working with both 21x181 and 20x190 by dropping the memory multiplier from 10x to 8x even though my Ram is specced at 2133mhz. On a positive note the pc can now exit sleep properly with Dynamic Vid on for 20x190.

Bit strange that at 4ghz I can use the memory multi at 10x fine with no problems whatever combination I use but oh well.

Thanks for all your help.
 
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