Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
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:

On the test pins behind plug ST16 measure the voltage across pin 1 and 3 (white and black wires on connector) with the connector attached to the PCB using the long shrouded probes.
Expect approx. 5V DC.
Note:
Plug shown for clarity.