Is unlinking CPU/memory a problem?

TJM · 29 May 2008 at 16:23

I installed an Arctic Cooler Pro 7 today and I'm now able to get my E6750 to 3.6GHz stable (temp is 38 idle, 57-59 during Prime95 tests) on an EVGA 650i Ultra. But I've had to unlink the CPU and memory speeds because the system is completely unstable with the CPU at this speed and the RAM (Corsair PC6400) linked. Windows bluescreened while loading with the two linked even when I had the CPU at 'only' 3.1GHz.

I tried increasing the voltage to the RAM to the maximum allowed by BIOS (2.1v) and used conservative timings, but the system locked up during POST.

It seems my RAM wants me to leave it alone. Will having unlinked CPU and memory speeds make any difference to system performance?

TJM · 29 May 2008 at 16:50

That's what I thought, cheers.

TJM · 30 May 2008 at 00:04

Hit a snag. I ran Small FFTs tests in Orthos and Prime95 for over half an hour each without a problem and completed the 32MB test in SuperPi, but if I run any test in Orthos or Prime95 that involves RAM one of the cores (usually the second) will fail in less than 30 seconds. The other carries on merrily.

Any ideas what could be causing this? I scaled the OC back to 3.2GHz, increasing voltage to the CPU (1.5, as high as I'm willing to go), the nForce SPP to 1.5 and even tried slowing the RAM below its stock speeds. Made no difference.

TJM · 30 May 2008 at 01:05

I've upped the memory voltage to the maximum the mobo will allow (2.1v) and slowed the RAM even further below stock speed. No difference.

I don't think there is an option in the 650i's BIOS to change the volts to the Northbridge. The System Voltage menu lists CPU FSB, CPU Core, Memory and NForce SPP only.

Edit: I reverted everything to stock settings and it's still happening. Running Memtest86 tonight to see if the RAM is damaged.

TJM · 30 May 2008 at 10:21

Figured out the problem. My second memory stick is borked - Memtest86 stalled at 28% during Test 2 on Memory Slot 1 and counted 31 million errors over night. I guess running it at the higher frequencies must have burned it out.

TJM · 30 May 2008 at 14:05

Ok, turns out there's nothing wrong with the memory itself. I spent all morning testing my two sticks individually in different slots and had no problems in Memtest at all.

There's nothing wrong with the memory until I put a second stick in. It fails Memtest during Test 2 and locks up the computer. I tried moving the sticks around the slots, but the results are always the same when two sticks are in. It reaches Test 2 and the error count for Memory Slot 1 skyrockets. Any ideas about the cause? I've already pulled out the CMOS battery to shake off any weird settings, but it didn't help.

TJM · 30 May 2008 at 14:44

Greebo said:
Try upping the volts on the northbridge. Make sure you are running the ram at the required voltage.

Not sure I can increase the volts on the Northbridge with this mobo. No option to in BIOS anyway.

Increasing the volts to the RAM allows it to get through Test 2, but it fails early in Test 3 on any voltage setting.

Finally borrow a mates ram and try that. If that does the same and altering settings doesn't work, then maybe your mobo is fubared

I don't know anyone with a desktop computer where I live, so I'm just going to bite the bullet and buy a single 2GB stick to replace my 2x1GB sticks. I hope this problem is with the number of sticks and not the memory size.

Rroff said:
Also if your overclocking a 650i board then decent northbridge cooling is MANDATORY - just putting a simple fan on the stock cooler is enough for upto 460 or so FSB - but if you don't it won't overclock very far at all once you need to increase voltages to the buses/chipset.

I'll keep this in mind, although I've got everything back on stock settings until I get this figured out. Which fan would you recommend?

TJM · 30 May 2008 at 19:43

I got a 2GB PC6400 stick on the high street today and Memtest did two passes without any errors. Orthos is chugging away now on the blend test, while previously it failed in less than 30 seconds. System seems stable at 3.6GHz, with all voltages on their default settings except for the VCore (increased from 1.24 to 1.33).

Shame about having to replace RAM that isn't broken, but oh well. Looks like I'll just have to avoid using more than one stick in this computer.

TJM · 30 May 2008 at 23:55

Rroff said:
If its stable with one stick but not with two then it sounds like the northbridge isn't getting enough voltage then - you should be able to increase the voltage to it but I don't know the BIOS on the EVGA boards.

I've checked every menu in BIOS and there's no option to do it. The manual makes no mention of it either. Weird, considering that a few reviews of the board make reference to being able to change the northbridge voltage.

Anyway, I'm happy enough with my system as it is. Just completed eight hours of Orthos without a hitch at 3.6GHz, with idle temps at 34-36 and full load temps at 57-59.