SA-8100 -36V on one amp channel output

[KeithD]

My SA-8100 that I recapped and replaced all suspect transistors has developed an issue. Output of power amp board (AWH-022-A) on one channel is reading -36V. Input on that channel (pin 16) is 0V. On this board I actually replaced ALL transistors in addition to the e-caps. I checked voltages at Q2 (KSA992) and Q1 (other channel):

E, C, B
Q2: -15.9V, -39V, -6.8V
Q1: 0.52V, -40.3V, -0.001V

Since the other channel is reading 0V output, I'm comparing readings on that channel with the bad channel. So assuming Q1 readings are normal, then there is trouble already at Q2.

I have not changed any of the diodes. Could one of those be suspect? Diodes are D1-5: 1S2473, D6,7: STV-4, D8-13: 1S2471. I have board revision A, which has D8-13 on the foil side.

Not sure what to focus on since all e-caps/transistors are new.

 

[rcs16]

It is best to do a working channel to dead channel comparison with power off, using the ohmmeter/DMM, un-plugged from the wall. make sure all the caps are discharged.
I check stuff like bjts, diodes tests (6-way bjt test), resistor tests, sometimes you have to lift a leg to get a proper reading. referring to the schematic and component placement, so have them printed out to work from.

Good Luck
Rick

 

[zebulon1]

Focus on all the things you did. Sounds like crappy advice but its true.
The amp is railed to one side?
If your reading the rail over the negative (-36v) side then the positive rail is not operating. Look on that side of the circuit.
The diff pair, the 992's are responsible for the balance. Check for correct placement and connections.