I would test the rectifiers the silicon is usually pretty resilient and normally grossly fails "open or short". I have only run in to one transistor so far that has "kind of" failed that one took a 576 to find it, was out of a fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac. The 400 series have switching power supplies they are not the linear supplies They can over current when the line voltage drops to low to regulate and can be damaged. Slow up on a varic is ONLY good for linear power supplies.
