Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Gain access to PCB (use Insulation Mat as required)
Disconnect connector at X501 and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage between connector X501 to a suitable earth point.
Voltage should now be approximately 73V AC.