Question BIOS reads 0RPM for system fan, they always go 100% speed

May 25, 2022
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Hello everyone!

I have a new case (Genesis Irid 505) and a Gigabyte MB (B450M DS3H). I've connected the Fan HUB, which holds 4 RGB fans to the MB's Sys_fan 1 (PWM) pin's. The cable has only two connection on the left and right side, so the two in the middle are missing. I am not sure if that is how a PWM supposed to look like. The system can't read the speed on the fans. When I go into BIOS and set the Sys_fan to PWM it suddenly calms down and I can controll the speed of the fans even tho it says 0RPM. The problem is when I exit the BIOS they return to their full speed. I have the latest stable BIOS version as well.

Can anyone please help? This is driving me insane :<
 

kanewolf

Titan
Moderator
Hello everyone!

I have a new case (Genesis Irid 505) and a Gigabyte MB (B450M DS3H). I've connected the Fan HUB, which holds 4 RGB fans to the MB's Sys_fan 1 (PWM) pin's. The cable has only two connection on the left and right side, so the two in the middle are missing. I am not sure if that is how a PWM supposed to look like. The system can't read the speed on the fans. When I go into BIOS and set the Sys_fan to PWM it suddenly calms down and I can controll the speed of the fans even tho it says 0RPM. The problem is when I exit the BIOS they return to their full speed. I have the latest stable BIOS version as well.

Can anyone please help? This is driving me insane :<
With only two wires, there is no wire to send RPM info back to the motherboard. That is why the zero RPM.
 
May 25, 2022
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I have a Fan Hub which connects to my MB with a 2 pin PWM so there is sadly no read on how fast the fans are going. In my BIOS I can control the fan speed blindly, but when I exit BIOS they just go full speed. Is there any software or anything I can use to manually send out blind feedbackless PWM signals to slow the fans down?

I have a:
Case - Genesis IRID 505 ARGB with factory fan hub
MB - Gigabyte B450M DS3H
 

Paperdoc

Polypheme
Ambassador
You may not need a new Hub. Let me explain how it is supposed to work.

The mobo system for controlling a fan speed does NOT need to know the speed of a fan. Its actions are based ONLY on a Temperature measured at a sensor on the mobo. The only thing a mobo fan header uses the speed signal for is to monitor that for fan FAILURE so it can warn you. So the header will alter the PWM signal it send on Pin #4 to the fan to change its speed, but it doe no need the speed signal coming back to it via Pin #3.

The cable connection you describe from the Hub the the mobo SYS_FAN header does not carry any fan speed signal back to the mobo, so you will never :see: and of the fan speeds anywhere. But it does send the PWM control signal to all the fans from the SYS_FAN header. You probably missed a small step in trying to set it. You have been using BIOS Setup to adjust settings on that mobo SYS_FAN header and that works for you. But once you have made a setting, use the Esc key back to the Main Menu (manual p. 20), then the F10 key to get to the Exit Menu (p. 35). There you must use the SAVE and EXIT option to save your new setting and reboot. This will ensure the BIOS remembers that and uses it in all operations from now on, not just within Setup.

Becasue this system cannot monitor a fan speed signal for failure, YOU should check your fans from time to time to verify they all are still working.
 
May 25, 2022
6
0
10
0
You may not need a new Hub. Let me explain how it is supposed to work.

The mobo system for controlling a fan speed does NOT need to know the speed of a fan. Its actions are based ONLY on a Temperature measured at a sensor on the mobo. The only thing a mobo fan header uses the speed signal for is to monitor that for fan FAILURE so it can warn you. So the header will alter the PWM signal it send on Pin #4 to the fan to change its speed, but it doe no need the speed signal coming back to it via Pin #3.

The cable connection you describe from the Hub the the mobo SYS_FAN header does not carry any fan speed signal back to the mobo, so you will never :see: and of the fan speeds anywhere. But it does send the PWM control signal to all the fans from the SYS_FAN header. You probably missed a small step in trying to set it. You have been using BIOS Setup to adjust settings on that mobo SYS_FAN header and that works for you. But once you have made a setting, use the Esc key back to the Main Menu (manual p. 20), then the F10 key to get to the Exit Menu (p. 35). There you must use the SAVE and EXIT option to save your new setting and reboot. This will ensure the BIOS remembers that and uses it in all operations from now on, not just within Setup.

Becasue this system cannot monitor a fan speed signal for failure, YOU should check your fans from time to time to verify they all are still working.
Thank you for your detailed answer. It had helped me to better understand the situation.

Sadly I do save the config in BIOS, since when I got back it has my settings set in, however fans still spin at max speed. When I set it back to Voltage and back to PWM is only when the PWM control takes action yet again. So BIOS saving is sadly not the issue
 

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