SA900C

[Diabolical Artificer]

Thanks for explaining the circuit and giving some pointers about adjusting idle I. I think I've found the problem with the sig pres circuit. I compared voltages to the working channel and found 0.6v on the collector of Q24, it should be +15v minus 1.7v for the diode approx. I followed the rail/psu back and found a 7815 voltage regulator had gone. Not sure how that works, but the led must be sourcing current from somewhere. So have some on order and will update then.

Cheers, Andy.