So, here I am with two M800 pcbs populated but not working. I can't see any soldering issues, and on one of the boards only 2 of the trimmers are working. So, I figure that I must have a bunch of dead trimmers or this particular style is grounding or something somewhere. I replace one with a different trimmer and find I can adjust the voltage. Great!
Following on from that logic, I replace the other trimmers and I can finally bias the j201s - but there's still no sound from the board. Oddly, one of the trimmers will bias to 3.5v or so, but then the most minute of adjustments will see it jump to 9v. Weird. Still no joy.
Anyway, I start looking at the board again and notice that one of the jfets doesn't have the same style of markings as the others. I look closer and find it's a 2n3609 or something (I didn't take any real notice) so I replaced that, adjusted the bias and we now have a working pcb. Now to replace the trimmers on the second board.
Following on from that logic, I replace the other trimmers and I can finally bias the j201s - but there's still no sound from the board. Oddly, one of the trimmers will bias to 3.5v or so, but then the most minute of adjustments will see it jump to 9v. Weird. Still no joy.
Anyway, I start looking at the board again and notice that one of the jfets doesn't have the same style of markings as the others. I look closer and find it's a 2n3609 or something (I didn't take any real notice) so I replaced that, adjusted the bias and we now have a working pcb. Now to replace the trimmers on the second board.