This thread has been going on for a while now and it seems no resolution as of yet. I had a look at the schematic at this amp just now. I had worked on a couple of these amps and one actually required the replacement of K1 and K2. They were burned out badly. Here is a set of possible problems I can see could prevent K1 (the on contactor) from turning on. You should be certain NONE of the following are the culprit. 1. On switch bad 2.Off switch bad 3.F1 or F2 open 3.R4 open or out of spec 4.R3 open or out of spec 5.K1 coil open 6. Contacts on K7 shorted closed 7.S5 interlock bad 8. Both phases of 240v line not present 9. Amp not properly strapped for 240v operation Those are a few causes I could find with a few minute examination of the schematic, there may be others but for sure you MUST check ALL of the above because ANY of or combination of the above will keep K1 from pulling in.