Question 4 wire fan acting like 3 wire

Mar 19, 2021
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I have case fans that are 4 wire, but it is acting like a 3 wire fan, and is humming as the mobo regulates its voltage. How do I get back to the 4 wire mode?
 

Paperdoc

Glorious
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The manual I found for the ASUS P5K-V mobo is dated from 2008. On p. 2-34 it says the board has a 4-pin header that uses PWM Mode only for the CPU_FAN header. The two CHA_FAN headers are 3-pin only. You cannot make them operate as 4-pin headers.

A backwards compatibility feature of 4-pin fans is that they WILL operate well and have their speed controlled by a 3-pin header (it uses the older Voltage Control Mode) although that is not ideal. What is it about their operation that makes you say they are not operating properly? Is it just the sound from them?
 

Paperdoc

Glorious
Ambassador
OK. Using a 4-pin fan under Voltage Control Mode is not supposed to damage the fan. However, that does not matter here since your fan is the CPU cooler. The manual indicates that the CPU_FAN header which has 4 pins can ONLY operate as a 4-pin PWM Mode port. BUT it does not say that specifically, and it is POSSIBLE that it really is using the older Voltage Control Mode. However, no matter which Mode it is using, you have no option to change that.

Here are two things you can check on and adjust if needed - see your mobo manual p. 4-26 and 4-28 under "Hardware Monitor".
  1. CPU Q-Fan Control should be set to Enabled.
  2. CPU Fan Profile should be set to Optimal so it CAN control the speed for you according to the measured internal temperature of the CPU chip.
If you make any change, remember to use the F10 key to reach the Exit Menu (p. 4-36), then the first option to Exit and Save Changes.
 

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