Question CPU fan turns on and quickly off

Jul 25, 2023
CPU: Ryzen 1700 with wraith cooler
Power supply: Gigabyte 850w
Mtherboard: B550 MSI Tomahawk

When I turn the PC on, the CPU fan (wraith cooler) turns on and quickly turns off and remains off. The CPU fan is plugged in the 4 pin fan header and has worked for about a month.

I plugged another 140mm fan in to the CPU fan header, the fan worked, the problem happens only when the CPU fan (wraith cooler) is plugged in, the CPU fan (wraith cooler) doesn't work.

The weird thing is, if I plug the CPU cooler in another fan header, the cpu fan (wraith cooler) works.

So the CPU fan header just doesn't like the CPU fan, I just can't understand why.

If it's the motherboard, then why does another fan work?
If it's the CPU wraith cooler fan, then why does it work on a different fan header?

I also tried a different power supply, and the same issue occurs.

Appreciate your help in advanced!


Mar 2, 2023
Does the computer stay on when you connect the 140mm fan to the CPU_FAN header on the mobo?

The BIOS probably checks the CPU fan speed (RPM) and if it's too slow, it powers down the CPU because it thinks the cooling is inadequate.

If the Wraith fan is faulty and running slow, it might trigger the minimum speed detector in the BIOS. If the 140mm fan runs faster than the Wraith (unlikely, but possible) it might satisfy the minimum speed requirement.