Is your board the GA-790XTA-UD4? The CPU FAN supports both voltage or PWM fan control. The bios detects automatically the fan type (3-pin or 4-pin) and sets the optimal control mode (DC or PWM). I think that those PWM splitters powered by the PSU will require that you change CPU Smart FAN Mode option in the bios from Auto to PWM. Myself I prefer PWM fans for heatsinks. They generally have more finite control than voltage based control methods.
2/4/14 at 3:00am