Sorry can’t see any pin numbers. I am getting continuity on what must be pin 1 on KN7 plug back to the mains plug but nothing on pin 2. So is there a break on neutral somewhere?
I have been trying the measure KN7 like you suggested but it has multiple wires on it. Any chance that KN2 is the power connector to the board? It only has a black and red wire and is supplying 21v.