Today I noticed my CPU cooling fan wasn't as loud as usual. Interestingly enough my Coretemp readings were higher than usual (60 degrees C and climbing) I went into BIOS and noticed fan speed was at 1229 RPM. Fan speed was usually around 3200 RPM.
I also noticed BIOS wouldn't let me change fan speed, no matter what I try. I tried disabling Q-FAN, saved changes and exited BIOS, no changes. I noticed the PWM interface disappeared, not allowing me to change fan speed.
So, I removed the 70mm fan and threw a 120mm fan on top. The fan spins at 2586 RPM. The CPU temperature has drastically decreased to 32 degrees C with a load. Much better.
So what I don't understand is why I couldn't control the speed of the 4 pin 70mm fan.
Did the 4 pin PWM controller on the motherboard fail?
Did the fan fail?
The motherboard is an ASUS M4A785-M
I've never had this issue before. Any help as to why the PWM interface has disappeared would be great. Thanks in advance.