Got a 1995 millermatic 150 that my dad has owned for years and he brought it over to me the other day saying it stopped working, he says it sounded like it was welding it self inside.

So I pull off the covers and have a look, I find the poles between the diodes are burnt off the SR2, my question what would cause this?

Don't want to order another one and turn it on just to have it take out the SR2 again?

Thx Railmen