CPU fan tries to start but does not spin

[Tom1]

My build is like my super pc today except no video card and one SSD. I turn everything off quickly. Everything seems to be connected properly. Since there is nothing connected but a monitor and keyboard I don't know how to troubleshoot. The case fan start ok.

[zburns]

CPU fan tries to start but does not spin Make sure the connector is fully plugged in. When it tries to start, give it a quick rotation like hit with a pencil eraser or a 'eraser', something firm but soft, to see it that helps. Assuming correct voltage going to the fan, that would indicate a defective fan. With the power off, the fan should spin freely and coast to a stop; if the fan stops very quickly with the power off, that tends to indicate bad fan. Is this the fan that came with the psu or not?

[Tom1]

I found that the cpu fan starting slowly is normal. I waited 10 seconds and the cpu fan started spinning. Intel made changes in 2012 using a new controller. Check out the following link for more information: http://www.intel.com/support/processors/sb/CS-033607.htm
Thanks again for your help.

[zburns]

That is pretty neat. At least one basic design of electric motors is that 'if the rotor is manually turned in one direction with power off' and voltage is applied to the motor while the rotor (motor shaft) is turning in the 'wrong direction', it will rev on up to full speed and continue to run in that direction.

What Intel may be doing is putting a 'system check' on rotation to be certain (1) the rotor is running and, (2), the motor is running at the right speed and in the right rotation direction. Running at correct speed is essential to 'properly' cooling the cpu.

Electric motors for normal operation, industrial, household or otherwise, are designed to start rotation in one direction only. When the voltage is applied, the motor 'kicks itself' (via the design) in the right direction. It is also possible, the Intel motor starts out slow as part of a 'system check' that the 'speed' is correct for the particular cpu temp because as the cpu temp increases, the fan speed has to increase -- it really matters that the fan speed is correct and can increase as cpu temp goes up.

Looking at the Intel link for more info, does state that the slow start is partially due to verifying direction of rotation. Anyhow, the main point is for a desktop computer to run for some years with perfect cpu performance, the fan that cools the cpu, has to be proven on each startup, that the fan is 'behaving normally' ! ! !.