Do you have 110 at recept, but only a slight sparkle when you try to weld? Does the machine go to high idle when you try to weld?
If it is your shunt field coils, they are dove tailed into the generator housing you will have to have a machine shop fix up a jig and press out the old olds and press in the new. Usually runs $100 for a machine shop that is set up for it.
You have to start at the control panel and work your way back piece by piece. Can explain in detail if you want. But it takes our shop approx 2.5 hours tear down time.