Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage between the red wire on A9 on the main PCB to pin 9 (purple) at the fan control board.
Expected voltage approximately 5V DC.