8 months since I first posted this thread and I see there has been a bit of activity with similar welders. I hadn't been near my welder pretty much since giving up last year. However with a new project in the garage I addressed this at the weekend. The PCB was diagnosed as working fine and the motor. What wasn't actually working was the Voltage selector in positions 1 and 2 used more commonly for thinner metal. All I had to do was clean the copper wires and re-connect and it seems to be working fine Can't believe that's all it was!