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Overclocking and Prime95 - my first major overclock - need help please

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Zithras

Registered
Joined
Jun 1, 2008
Computer I'm making:

CPU Q6600 G0 SLACR (lapped)
MB: Gigabyte GA-X48-DQ6 (unfortunately, it's so new that its hard to find info on)
cooler: TRUE (also lapped) with scythe 120mm 100+ cfm fan, on tight with 'penny' (well...dollar coin) mod
PSU: PC Power and Cooling S75Qb 750W
video: Zotac GeForce 8800GT 512 MB
ram: G.Skill 4 GB (2x2gb) DDR2 1066 (mfr. specified voltage is 2.1, with 5-5-5-15 timings, when the motherboard is set to autodetect timings, it gets 5-7-7-20, right now I have it dialed in to the recommended 5-5-5-15 timings, but running at 800 instead of 1066 for a 1:1 ratio)
fans: 5x Thermaltake A2016 80mm variable case fan

I posted earlier about a heating problem, and later figured out that the Xigmatek heat sink was not clamping hard enough onto the processor, and two pushpins refused to hold. So, I got a TRUE, and that problem's solved - no more overheating :D. On to the next problem!

Since the BIOS only lets me set ram timings corresponding to 2.4, 3.0 and 3.6 GHz CPU FSB speeds, I'm trying for a 3.6 overclock, which should be more than doable with this board and cooling setup - but it's not working (I'd be happy with 3.4, but the board doesn't support it, and I don't want to go as low as 3.0).

I set the stock voltage rather high, at about 1.481, (stock for the 6600 is 1.3, with Intel stated max of 1.55) and started up the computer, with the intention of slowly working my way down voltage-wise until the computer became unstable. The board posted with no problem, but I started getting errors when running Prime95 (large FFTs, 4 threads). I assumed the voltage was still too low and adjusted higher. Same story when I upped the voltage to the low 1.49s. Once I hit 1.50, however, instead of giving me an eventual rounding error, the computer just started locking up after about 2 minutes! No error message, no warnings, just a lockup. I raised the voltage again to 1.51 and the same thing happened.

At no time did the CPU core temperature go above 68C, so I doubt its overheating.

Any ideas as to what I'm doing wrong? Are my voltages too high? Too low? (Is it even safe to put a Q6600 at/above 1.5V even if it's not overheating?)

How can I tell if my voltages are too high or too low?

Anyone with a similar setup have an idea on what voltages I should try?
Any other information I should post?

Thanks for your help!
Zithras
 
Welcome to the world of overclocking :)

Every cpu is unique in terms of its OC-ability, and what it will take voltage-wise to get there. Someone correct me if I'm wrong, but I think most Q6600s, if they're going to hit 3.6 stable, will do it with less than 1.5 Vcore. IMO 1.5 is a bit high.

From my limited experience, a good Q6600 will do 3.6 with about 1.45 Vcore. If it doesn't do it with 1.5, I'd say it either won't do it at all, or the problem lies elsewhere. For example I'd be running MemTest to see if memory errors are to blame.

Your temps, if accurate, are within reason. I've done P95 testing and have seen temps up to 85 C and my rig has remained stable. Not ideal temps at all, but the point being that under 70 is good IMO.
 
Memtest86+ ran 8 clean passes, so that's not the problem. I've messed with settings for awhile, with no luck. I guess this particular CPU just won't hit 3.6.

I'm thinking I'll set it at 3.4, and unlock the memory ratio/set the memory to 1066 dual channel.

Does anyone know how to enable asynchronous memory multipliers (i.e. get them to show up) in the AWARD BIOS used in the X48-DQ6? I.e. I want the RAM linked but unsynched to the FSB. (The default synch settings only apply to 266, 333, and 400 FSB)
 
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