Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Disconnect the harness which runs from the display PCB to the main PCB
Remove the display PCB from its housing
Plug the display PCB directly onto the main PCB
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With the display PCB plugged directly onto
the main PCB does the display illuminate ?
Note:
At this point do NOT reconnect the harness and refrain from
attaching the display PCB back into its housing.