Question CPU fans randomly stop spinning.

Pytheus

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Oct 28, 2020
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Noticed my CPU fans just randomly stopped spinning. They try to starting up again but then stopped. Restarting the PC seems to have fixed the problem but this has made me nervous, can't leave the PC on unattended now. I want to know the cause so I can fix any future problems.
I have two fans in a push pull config on a Hyper212 heatsink. One fan is plugged into the CPU fan header, the other the CPU_OPT header, both stopped at the same time.
ASUS B-550F Mobo
5600x CPU
3060ti GPU
Seasonic 750W PSU
32GB RAM
 
Last edited:

Paperdoc

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Post back here with the maker and exact model of your mobo. I suspect you have the CPU_FAN header set to use a minimum speed that is so low it allows those fans to stall. When that happens, and automatic system detects the stall and re-starts the fans with a higher-speed power pulse. But then the normal system returns and causes it to stall again. etc., etc,.... By looking at your mobo's manual we can advise how to alter a BIOS setting to fix.
 

Pytheus

Prominent
Oct 28, 2020
82
19
545
4
Post back here with the maker and exact model of your mobo. I suspect you have the CPU_FAN header set to use a minimum speed that is so low it allows those fans to stall. When that happens, and automatic system detects the stall and re-starts the fans with a higher-speed power pulse. But then the normal system returns and causes it to stall again. etc., etc,.... By looking at your mobo's manual we can advise how to alter a BIOS setting to fix.
Its the ASUS ROG STRIX B550-F GAMING (WI-FI)
 

Paperdoc

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Thanks for that. Unfortunately the manual for that mobo shows no details on the options available in BIOS Setup for the CPU_FAN header. (The CPU_OPT header you are using for the second fan just mimics exactly what the CPU_FAN header does.) The only hint we get on the mobo web page is a list of options for Q-FAN Control. OR, you may be able to find these using the Fan Xpert utility.

Go to the CPU_FAN configuration screen. The options for general control strategy (often called Profile) usually include Standard, Silent, Turbo, Full Speed, and Manual or Custom. SOMETIMES there will be a place to set a fan minimum speed, but often there is not. Sometimes there is an option to allow or NOT allow the fan to be stopped by the automatic system. However, you CAN make this adjustment using the Manual or Custom option. That choice allows you to set up your own version of the "fan curve" which specifies what speed to run the fan for certain temperature readings. You simply adjust the low speed setting for the coolest (and maybe second-coolest) temperature points to be higher than you have them now. Try a few new settings to see what eliminates the fan stalling. When you make changes, remember to return to the Main Menu using the Esc key, then F10 to get to the Exit Menu. There choose SAVE and EXIT.
 

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