I have a completely weird fault in a friend´s M2500. The desk blows mostly the -17V rail, sometimes the fuse (10A) is gone, sometimes the regulator card (GL48 see appendix) shuts off. I´ve replaced the socket of it´s LM338K since it was burnt and the LM338 also had a burnt pin. With the repaired regulator the desk worked shortly, then the +17V rail blew, not the fuse but it´s regulator shuts off. While searching for the fault it stopped shutting off but then the 11V logic rail showed the same behavior. I found a faulty subregulator in the master section which brings 11V down to 5V. After that repair the desk worked for 10 minutes, then again the -17V rail shuts off. I have no idea what fault could create this behavior.
When I was working on the -17V rail for the first time we started with measuring current of the -17V rail with the empty desk frame, then inserted channels and accordingly measured. The weird thing now is that all the figures made completely sense. There was no single channel drawing so much current, that it could have blown either a fuse or cause the regs to shut down. At the end of the day we had no solution and I had to leave the studio with a non working desk. Next weekend we´ll try again, but I need some ideas where to look at.
But by writing this it occurs to me that maybe the crowbar circuit could somehow be activated, but this doesn´t give me an explanation with the other rails misbehavior.
Any ideas????
