Change of case fan upsets overclock

sebjames · 3 Jun 2011 at 15:49

I have a Core i7 2.8 GHz on an Asus P6 motherboard, supplied as an OCUK overclocking bundle clocked up to 4GHz, cooled by a Noctua heatsink. I'm using a Corsair HX650W PSU, 6 GB of Corsair RAM, 4 regular SATA HDDs, a 3ware RAID card and some cruddy Asus gfx card which came from a Dell PC.

It's been running very stably (until a forced reboot, I had uptime of 193 days for a workload of software development - lots of software builds). I now need to change one of the case fans from a 5W server-type fan to a quieter 1W fan.

Oddly, with the less power hungry fan, the mobo refuses the overclocking settings (which I never changed from OCUK's set up).

I'm guessing the different fan is affecting the 12V rail in such a way that the mobo is unhappy.

I may try adding another fan to see if the mobo will allow the overclocking.

If I had to "back off" the overclocking - say to 3.8 GHz, how should I do that? Which is the best setting to pull back on for an i7?

Thanks for reading,

Seb James

spleenharvester · 3 Jun 2011 at 16:10

Might sound like a silly question, but what are the temps? If it's running hotter than it did with the old fan it could cause an overclock to fail.

sebjames · 3 Jun 2011 at 16:26

I'm fairly sure it's not a thermal issue. This happens after the machine has cooled down for some time and at no point will the motherboard allow me to boot with the overclocked parameters.

I think if I had a problem relating to reduced airflow with the lower power fan (there are about 4 other fans in the case) then I'd only notice this after a period of operation.

fleming222 · 4 Jun 2011 at 12:59

Does the PC run at default speeds with the new fan?

ScratchFive · 4 Jun 2011 at 17:32

what are the symptoms? do you get a post? if you don't its unlikely to be thermal.

the 1W fan will have a higher resistance than the 5w fan, so could potentially affect the 12v rail, however as the 12v rail is regulated in most (all?) PSUs I think we can rule out the possibility that your overclock has gone from fully stable to refusing to cooperate in basic tasks... the only way i can see this being an issue is if there is a short or fault with the fan and it is drawing A LOT of current. check if its getting hot.

if you can get into bios, save the oc profile (or write down the bios settings if you don't have the option to save) and load setup defaults, this will mean you can rule out the overclocking as a factor.

hope this helps

sebjames · 6 Jun 2011 at 09:49

Thanks for the replies folks.

I've decided the case fan is a red herring.

The motherboard does go through POST in all cases.

It seems that after a reboot and POST, the P6T motherboard will often say "overclock parameters failed" (or similar words to this effect; I forget the exact terms).

I mistakenly linked this to a change of the case fan, but I think it's unrelated. As ScratchFive notes, the 12V rail is regulated and unless something fairly serious was wrong, the different fans aren't going to make a lot of difference there.

I can resolve the issue by going into the P6T setup and reloading the OCUK-provided overclock settings.

I don't know why this works, but it seems ok. Once booted, the system is very stable.

So this isn't a case fan issue, it's more a "why does the P6T not like to reboot with OCUK settings?".