I have one miller xmt 400 cc dc inverter arc welding machine. I faced the problem that the out put diodes are going short after first touch.i changed all diodes with new one but still the problem is same.i also changed the igbt module with part no MG75Q2YS1 where as the orignal part no is MG75Q2Ys11.Is there any problem with igbt module or some thing else. before touching the rode machine is working properly.please guide me.