Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Gain access to PCB (use Insulation Mat as required)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Ensure no demand, and fan is not running.
Measure the DC voltage between pin 7 (yellow) and pin 9 (purple) at the fan board.
Expected voltage approximately 0.5V DC.