CPU Fan not working

liamkoni · December 12, 2019

Hi there,

This is the first PC I have built by myself, and everything is working great but I can't get the CPU fan header to power my fans.

I have a ROG STRIX B450-F with a Ryzen 3600. The motherboard has several fan headers (CPU_Fan, CPU_Opt, CHA_Fan1,2,3, and AIO_Pump). I have 6 fans in total. The three with the case (corsair LL120), I have connected to the chassis fans headers, and am using them for my AIO radiator (coolermaster Ml360r). The three fans that came with the radiator I am using as chassis fans. The radiator came with a fan splitter, so first I had the three of them connected all to the CPU_Fan header, but they wouldn't spin and on boot the motherboard was detecting a CPU fan error and refusing to boot. I then tried various swaps and plugging different fans into different headers etc. Results were that: the coolermaster (CM) fans all worked fine when plugged in individually or with the splitter into the CHA_FAN1 header. The CM fans would not work when plugged individually into the CPU_FAN and CPU_OPT headers. The LL120 fans work fine when plugged individually into the CPU_FAN header. Also, when the CM fans were plugged into the CPU_FAN header either individually or with the splitter, when powering the PC on or off, the fans that were connected would all jerk a little bit.

This leads me to believe that there is some issue with the CM fans with the CPU_FAN and CPU_OPT headers, but I cant for the life of me figure out why that would be the case.

Cheers,

Liam

The Spectator · December 12, 2019

Only thing i can think of is a faulty port, maybe flash the BIOS or CMOS?

Good Luck!

Pharr Carnell · December 14, 2019

it could be an issue with the motherboard headers having the capacity to deliver enough power to supply all the fans that you want powered. I'd be very wary of trying to power 6 fans from just the motherboard headers...yes you can buy splitters to enable multiple fans to be powered by a single fan header; but you run the risk of 'demanding too much power' from the 1 fan header which could damage the motherboard itself.

My suggestion would be to source a quality Fan Controller of the 5.25" variety that fit into a spare optical bay slot; they're usually powered by a sata or molex connection that does provide sufficient power, but if your case does not have optical drive port, then you're limited to the type of 'multi'split' connectors which usually attach to the case somewhere using double sided velcro or tape...the type you see in eBay adds for RGB fans with remote controls; do some research there to understand they type of multi-connectors that are available...then decide your best course of action. I have a Coolermaster Cosmos II case that runs about 9 fans; but they're all powered by connections from the case itself...none of the motherboard fan headers are used except my CPU fan which has my AIO pump connected to it.

Just be very careful to not overload any motherboard headers...