SYS_FAN2 connector needs any fan, with three or four wires (don't care) since the speed is controlled via on-board PWM controller that supply pulse-width-modulated 12v for the fan via pin 2. So, if using a four wire fan, its internal PWM is locked to full speed (this explain that fixed 5v on pin 4). This time, the mobo senses the North Bridge temperature and will increase or decrease the speed of the fan connected in this socket. Feedback is sent to pin 3 for BIOS alarm purposes.
Comment