I think I might have had a minor breakthrough. I plugged the amp into the mains directly and within a few seconds the 3 amp fuse on the negative rail blew. That at least pointed me in a certain direction. There's a Mosfet (Q402) that according to the component list is "selected" and colour coded yellow. The paint on the top surface of the FET is cracked as if from overheating. There's a clue. So I'll remove it and check it out. Of course it may not be available these days....ho hum.
Q402 and associated parts are low power, unlikely to fail and even less likely to blow a 3 Amp fuse. Read post #20 again. You probably have a shorted output device, Q314 - Q317. Check with the Advent 300 unplugged from the mains and use a meter to measure resistance collector to emitter for each output transistor. If one or more devices are shorted, Mouser has replacements. Check the driver transistors too if an output transistor is shorted.
Just a note about testing the Advent 300: I had problems using a dim bulb tester with this unit. It seemed to mess up the start-up timing and caused it to go into an odd state between powered up and powered off.
Just a note about testing the Advent 300: I had problems using a dim bulb tester with this unit. It seemed to mess up the start-up timing and caused it to go into an odd state between powered up and powered off.
Attachments
One detail, to prevent
Many amps "wake up stupid" and latch halfway if required to feed any current to a load.
You ar still at the "shorted" stage but later you may find this, so first turn amp ON and later connect speakers, after you have checked for no voltage at speaker out. (less than 100 mVdc)
tun amp ON, THROUGH bulb limiter but WITHOUT load (no speakers connected).
Many amps "wake up stupid" and latch halfway if required to feed any current to a load.
You ar still at the "shorted" stage but later you may find this, so first turn amp ON and later connect speakers, after you have checked for no voltage at speaker out. (less than 100 mVdc)