Jeff, BINGO, you hit it right on the head! Q4 collector was loose. I pressed on all the transistor connections with an insulated rod, and when I got to Q4 on the 40 watt PA it came to life. I touched up the connection with a big iron and it now puts out 125 watts with 34 amps draw. I turned it back to 75 watts and 17 amps current.
I think I'll look for a replacement board instead of doing surgery on this one. At least it's up and running and I can continue working on getting it ready for service. Thanks Jeff, and everyone else who gave me some good suggestions. 73, Joe, K1ike Jeff DePolo wrote: > > 1. The driver (40 watt) transistor has developed a cold solder joint > at the > collector tab. Try heating it up with a high-powered gun to get the solder > to reflow. If it starts working, that's your problem. But you're not done > yet. You need to diligently remove all of the old solder, including > burned/hardened residue on the PCB trace and underside of the tab, before > laying down new solder. Even if you do this well, there's still a good > chance that the plating on the tab is ruined and the problem will > return in > the future. >
