CPU fan stuck on full throttle at power-up

Equilateral · Post by **Equilateral** » Thu Jul 01, 2010 6:42 pm

For the last month or so my previously-silent system has had an intermittent problem where the CPU fan is stuck on full throttle at power-up. I've had the system for about two years now and it's only just started happening, generally if I leave it to run for about 15s, power it down again, and then restart it everything is back to normal (meaning the fan sits at 0 rpm most of the time, occasionally spinning up to 300 rpm and then stopping again - it's a pretty efficiently-cooled system, and not under much load). The MB is a Gigabyte P35-chipset one and the cooler is a Xigmatek 1283 with PWM control.

Does anyone have an ideas what could be causing this, and how to resolve it? It's intermittent (only happens about 50% of the time when starting the system), can be resolved by a restart or two, and has only cropped up in the last month or so. It'd be nice to be able to fix it, both because the multi-stage startup is a pain and because repeatedly power-cycling the system to get a clean start won't be good for it.

Equilateral · Post by **Equilateral** » Wed Jul 07, 2010 9:48 pm

In case this provides more information, it seems to be something controlled by the BIOS at power-up, if I manage to get into the BIOS setup before the boot process continues and then, changing nothing, select "Save and exit", the system restarts with the fan running at the correct speed (which in this case is 0 rpm). If anyone has an suggestions (apart from the obvious "reflash the BIOS"), I'd be interested in hearing them...

Post by **MikeC** » Thu Jul 08, 2010 11:19 am

Equilateral wrote: If anyone has an suggestions (apart from the obvious "reflash the BIOS"), I'd be interested in hearing them...

I can only think of the obvious...

Equilateral · Post by **Equilateral** » Sun Jul 11, 2010 10:46 pm

MikeC wrote:
Equilateral wrote: If anyone has an suggestions (apart from the obvious "reflash the BIOS"), I'd be interested in hearing them...
I can only think of the obvious...

The downside is the nonzero chance of bricking the MB... I'll see how desperate I get, by trial and error I've found that just going into the setup and exiting without saving is enough to fix it, my guess is that at some point fairly early in the BIOS init stage it's getting the fan speed setting wrong, and a restart is enough to fix it.

Redzo · Post by **Redzo** » Sun Jul 11, 2010 11:30 pm

flashed tens of motherboards (if not hundreds) never "bricked" anything...

chienpourri · Post by **chienpourri** » Mon Jul 12, 2010 4:51 am

Yeah - the risk is pretty minimal unless you download the wrong bios (in most case you can see it before actually chossing "yes") or unless of course you lose power (if you try to flash your bios during a thunderstorm for example - nothing a good APC unit won't handle). I always keep my BIOS / firmware for SSD and Burners up to date to have the latest fixes / improvements. Never had a failure in over 20 years! Only thing is wait at least 2-4 weeks after a FW has been released so you won't be a guinea pig.

themaster1 · Post by **themaster1** » Mon Jul 12, 2010 5:37 am

Yep the obvious is the Bios settings here. Disable / re enable "smart-fan" in my case. Then there is the Vbat (bios battery) to consider, generally it last several years but you never know.
Mine gets old (4 y.o.) it only deliver about 1.98V (should be 3V) at the moment, the pc still boot up / store the settings but for how long i don't know, Anyway i just bought 2 new today.