Is my CPU fan causing my other fans to run slowly?

[Filonzo]

Whenever I plug my CPU fan into to the correct connector on the mobo it causes all of the chassis fans to slow down and there seems to be this high pitched screeching sound when I have my PC running. I stopped it by switching the cpu connector with the chassis fan connector and it works fine but it means that the cpu fan is running at full speed. Does anyone know why this might be happening?

Thanks

 

[Karadjgne]

Sounds like a short in the mobo or mobo/case if the backplate is touching solder joints. Very surprised the pc is running, almost always the cpu_fan header must be populated or the cpu will initiate shutdown to prevent instant overheat.

 

[R0GG]

Most likely is a combination of speed curves of CPU-FAN / Motherboard SYST-FANs Bios or Windows settings.
Best is to keep your CPU-FAN connected to it's dedicated motherboard CPU-FAN header and adjust it's duty/curve in Bios, then in Windows preferably through your motherboard manufacturer dedicated FAN tuning utility or a third party tuning utility app, fans speed are supposed to adapt to CPU and motherboard key sensors temps (which you could monitor using Hwmonitor application) to keep system and CPU cool with minimum noise and RPM possible, and adjustable on demand as well.

What are your system specifications ? (motherboard brand and model, CPU, CPU cooler model, and your case fans models (3pin or 4 pin fans?)

 

[Filonzo]

Thank you for the tips. This build is a couple years old but I’ve got by with the cpu plugged into the chassis fan port. I fear now that it may be overheating as it shut down when I was playing games the other night. I replaced the thermal paste but haven’t got around to testing it again. The specs are as follows...
Mobo: ASUS M5A97 LE R2.0
CPU: AMD FX 6300
Case fans: Corsair Fans 3pin, can’t remember if they are AF or SP.
The CPU cooler is stock, was thinking of replacing it with an aftermarket one.

 

[R0GG]

Did you at some point get Bios error message at Bios Post " no CPU fan", it's safety measure in most motherboards ensuring CPU is cooled but could be overridden in some motherboards (did you override it at some point to get your system to boot with CPU FAN attached to SYST FAN header instead of CPU one?)
Could you upload screen capture Hwmonitor showing CPU temps, CPU Fan speed, System Temps and Syst fans speed at idle and while gaming , which by the way duty curves are strongly recommended to be adjusted accordingly through software or/and bios if overheating occurs.

 

[Karadjgne]

His board won't have that option it's a M5A97 LE and LE does not stand for Legendary Edition, more like Lame Excuse. It's basically the board you'd find under the bottom of the shelf. Sorry Op, but I have a LE too.

I'd do a thorough visual of the mobo, especially the cpu_fan header, make sure pins are straight, and the back where the solder joints are.

One other test you can try is just use the cpu_fan header, unplug all the case fans, see if that works. It might be a case of you have too much power being drawn on the Isa buss that runs the fans.

 

[Filonzo]

His board won't have that option it's a M5A97 LE and LE does not stand for Legendary Edition, more like Lame Excuse. It's basically the board you'd find under the bottom of the shelf. Sorry Op, but I have a LE too.

I'd do a thorough visual of the mobo, especially the cpu_fan header, make sure pins are straight, and the back where the solder joints are.

One other test you can try is just use the cpu_fan header, unplug all the case fans, see if that works. It might be a case of you have too much power being drawn on the Isa buss that runs the fans.

 

[Filonzo]

Hi guys thanks for the help but I’ve determined that it may be problem with mobo itself, you’re right in saying it’s a lame excuse haha. The cpu fan works fine on its own, the problem occurs when I plug in a third chassis fan, doesn’t matter which one. All the fans slow down, sometimes even stop and a high pitched whirring sound starts coming from what I think is the fan motors. Not sure if there is something in the BIOS that may be able to solve this. It might be that I a new motherboard.

 

[Filonzo]

Oh and I haven’t had any cpu fan error messages either, there was nothing to override. The mobo just lets me swap the fans around. Strange how all the fans work when the cpu fan is plugged into a chassis header.

 

[Filonzo]

Update: was monitoring the temps while gaming. Everything fine until the GPU hit 60c and the fans kicked in causing the other fans to slow down, the cpu temp goes up as a result and shuts off when it hits 90c. It’s like there’s is not enough power being shared between the fans.

 

[R0GG]

@Fiolonzo Quote " Update: was monitoring the temps while gaming. Everything fine until the GPU hit 60c " you probably mean CPU temp.

Your motherboard has 3x 4pin system fan headers and 4pin CPU fan header, and it's Bios has an extensive Fan control adjustment (similar to my motherboard Asus Crosshair formula V) when enabling Asus Q-fan control in Bios for CPU and/or Chassis Fans, you''ll have low RPM warning and lower/upper operating temp and Min/Max operating duty cycle for each fan, on top of the quick CPU/Chassis Fans quick profiles (accessible/adjustable also under Windows through Asus proprietary Fan Xpert application (standard, silent, turbo, manual) , in my humble experience chassis fans speeds are cross-influenced by CPU fan curve which could be painful to manage (at times it's tricky to get desirable low noise efficient RPM for chassis fans as they are group controlled and not very accurate but does the job well)

Your motherboard manual >> http://dlcdnet.asus.com/pub/ASUS/mb/SocketAM3+/M5A97_LE_R2.0/E8047_M5A97_LE_R20_V2_WEB.pdf

Asus Fan Xpert app: page 104
Asus Q-fan and fans settings page 76

 

[Karadjgne]

So with cpu fan in cpu header by itself, all sys fans unplugged, it works fine? And plugging in 2 out of the 3 sys fans for a total of 3 fans, it works fine. Just when the 4th fan is plugged in it goes nuts?

Mobo issue. It's pulling too much power on the buss feed. Or, your system/cpu fans are pulling too much power individually, which the boards are rated at @1A per header, should be @3A total available. Some older fans could pull 0.5A each or more, some pulled as much as 1A each, so if the buss feeding all the fans has gone bunk, with all 4 fans you are pulling too much power from the mobo. Which again is a mobo issue.

I'd contact Asus support directly, Asus boards (I have an Asus p8z77-v LE) have a security failsafe on the cpu header and will not allow the cpu to boot if there's no fan, or if it detects 0rpm will shutdown the pc. So even having the cpu fan in a sys_fan header, that leaves cpu_fan header blank and you should not be able to boot at all.

With qfan, that cpu warning is just that, a warning that shows up on screen that you set. It's independent of the security setting of unpopulated or 0rpm failsafe.

 

[Filonzo]

Yep it runs fine with two chassis fans and the cpu fan in the correct header. I’m monitoring temps with the one intake and they are fine when gaming. The fans don’t slow down when the graphics card fans start either. So yeah mobo issue. Will just have to make do with two case fans until I get an upgrade. The case fans I’m using are three pin so no speed control. Thanks for your help guys!

 

[R0GG]

I would try enabling Q-fan in Bios and playing with Asus Fan Xpert for a little bit, I know it could be a little tricky to get desired fan speeds especially with the lack of accuracy of chassis fan curve, lack of individual fan control (at least in the version I am running) and the "sensitivity" of chassis fan speed with CPU fan curve adjustment with Fan Xpert. It could be some Bios fan setting interference when third fan is added. I don't particularly like the buggy at times Fan Xpert but it gives decent and much simpler overall control over CPU/Chassis fan speeds without the need of third party app or a dedicated chassis fan controller add on.