CPU fan speed at 100%

[tigersty1e]

So I've had my cpu fan set at pwm in my bios and it has worked perfectly. 1500 rpms with ~30C and ramps up to 2700 rpms under load.

But lately, every 1 out of 3 times I turn on my computer, my cpu fan will be spinning at 100%. A reboot fixes it, but I want to fix this thing.

When it does ramp up, 1 other fan connected to my psu also ramps up. (but the other 5 fans don't change)

 

[Paperdoc]

So the system worked perfectly from the start, but recently has become intermittent. This suggests the fans and the BIOS are not the problem. The most likely source is a poor connection at a plug. You could test for this by running software (or use your BIOS screens) to look for what the BIOS believes is the actual speeds of the fans involved. My suspicion is that it's getting a poor signal and believes the fans are running slower than full speed, so it is trying to speed them up by supplying full voltage to them. See if the fan speeds are shown as less than full speed. If that's the problem, there may be a simple fix. Shut down, disconnect the power cord, and open the case. Look for the two mobo connectors for the CPU Fan and PSU fan. At each, just pull the connector off and then re-insert it, two or three times. This action will "scrub" the contacts of any light oxidation. Close up, connect the power cord and start up. That just may stop your problem.