Case or CPU fans running at 100% full speed all the time (DC mode)
4-pin PWM fans are configured as 3-pin DC (voltage controlled) in , supplying a constant 12 volts and forcing unbearable fan noise at idle.
Internal desktop parts run on harmless 12V DC voltage and cannot shock you. Simply unplug the wall power cable first, then touch the unpainted metal case frame to ground static electricity.
Common Symptoms & Tells
- Fans run at deafening maximum RPM from the second the PC powers on
- Fan speed never drops, even when CPU temperature is 30°C
- Software fan control tools (Fan Control, SpeedFan) have no effect
Interactive Fix Checklist
0 of 4 steps completedEnter BIOS setup and open Hardware Monitor / Fan Control
Restart PC and press Del or F2. Navigate to 'Q-Fan Control' (ASUS), 'Hardware Monitor' (MSI), or 'Smart Fan' (Gigabyte).
Switch Fan Control Mode from DC to PWM
Select each fan header (CPU_FAN, CHA_FAN1, etc.). Change the control mode from 'DC' (or Auto) to 'PWM'. 4-pin fans require PWM pulse signaling to modulate speed.
Run automatic fan tuning calibration
Click 'Fan Tuning' or 'Optimize All' in . The motherboard tests minimum starting voltages for each fan to prevent stalled fans at low RPM.
Use Fan Control (open-source software) in Windows
Download the lightweight, open-source 'Fan Control' utility to bind case fan curves to both CPU and temperatures simultaneously.
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