Hi EddieAll the diodes in that 1N54xx series are 3 Amp diodes, the only difference between -00 to -08 is the value of the peak inverse voltage. In a single-phase inverter MIG welder the maximum voltages are 230 AC and 325 DC. I suggest that you chose a 1N5405, which can work up to 350 AC and 500 DC.
Apart from this diode, have you checked through the suggestions linked in my post #12 above ?
Yes I have already done all your suggestions before I joined this forum, I have done visual with microscope all looks fine on the motherboard that is why I moved to testing Components. I Appreciate all your help and advice, I will have to order the diode, I've checked the motherboard, my next check will be the Daughterboard, which I think will switch on the main board. All the best Sid