Lincoln Tig 300/300 problem

admin

I have a Lincoln tig 300/300. It starts up and runs fine but has no amperage control with the fine adjustment dial. Switching the large range knob does cause the amperage to rise and fall properly, but it appears as it only welds to the minimum amperage in each range. I have rebuilt the PC board as this has caused similar problems in the past. But, no change with the new board. Any ideas will be appreciated. The machine is older but in very good shape.