I have a Pioneer SX-780 that powers up but produces no sound and no relay click. The STK's (Darlington power packs) are good. I would like some help tracing the signal. I have test equipment that I have picked up over the years. Mostly at garage sales or Craigslist. I have two SX-780's one that works and one that doesn't. I was thinking I could probe around and trace the signal, which would lead me closer to the issue. I thought it would be easy because I could use the working unit as a base line. However this is much harder than I expected because I don't know where to put the probe. I know for sure that the Darlington Power Packs are good because I swapped them out of a working SX-780. The unit passes the Dim bulb test. The unit powers up, the three lamps, source, and tape monitor lights come on but the relay doesn't click No voltage to the VU Meters FM needle is dead The rail voltages are +40.6v and -40.6v I tested the three transistors on the heatsinks Q25, Q19, Q20 and resoldered them. They all tested good. Q25 E 13.7v C 27.3v B 14.4v Q19 E 40.4v C 51.5v B 41v Q20 E -40.4v C -53.3v B -41.1v R1 The big ceramic resistor mounted on the chasis tests 26.7v and 51.9v The emitter resistors all measure .4 ohms NO signal when probing at R233/R234 (the input to the power amps) Opamps TA7136 Q3 and Q4 are suspect not even close to specs. Q3 pin7 -21.8v pin6 -24.6v pin5 -21.2v pin4 -24.8v pin3 -21.3v pin2 -20.6v pin1 -21.2v Q4 pin7 -21.8v pin6 -23.9v pin5 -21.2v pin4 -24.8v pin3 -21.2v pin2 -20.6v pin1 -21.2v STK-0050 Left STK (looking at front of unit) pin1 39.2v pin2 -41.3v pin3 39.2v pin8 39.2v pin9 41.3v pin0 40.3v Right STK (looking at front of unit) pin1 -1.1v pin2 -41.4v pin3 4-9mv pin8 18-25mv pin9 41.3v pin0 1.2v Side note when I first got the unit it powered up the relay clicked but no sound. Now after replacing the STK's the relay wont click.