Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect M4 from the PCB
Measurement:
Test 1:
Measure the resistance between the 2 outer wires (brown and dark blue) at M4.
Resistance should be approximately 235Ω
Test 2:
Measure the resistance between the brown wire at M4 to a suitable earth point.
Resistance should be greater than 1MΩ (or O.L)
Measure the resistance between the 2 outer wires (brown and dark blue) at M4.
Resistance should be approximately 235Ω
Test 2:
Measure the resistance between the brown wire at M4 to a suitable earth point.
Resistance should be greater than 1MΩ (or O.L)
Isolate as per TOPs P4
and refit as necessary