Onkyo A8200 - Not the right voltages in some transistors

[Francesc V.]

Hi:

I am trying to repair this amplifier that I've bought as faulty. I've found some transistors damaged, the ones where I am drawing a red circle.

With the final transistors not yet installed (the expensive ones), I've started to measure some voltages:

Where I am supposed to have 1.12V (base Q524/Q523) I am reading -42V..................both channels don't seem ok.
Where I am supposed to have -1.12V (base Q526/Q525) I am reading -44V..................both channels don't seem ok.
I removed and tested Q514,Q516 & Q513,Q515 but the analyzer tell the they are fine.
Potenciometer bias seem ok (R530 & R529)


Maybe readings are correct and notes in the service manual aren't.........but I don't think so, as long as Q524 gets really hot without any load.

What might be causing this anomaly? I've attached the service manual for the whole picture.

[Francesc V.]

Not sure if I am going in the right direction, but my problem is this -41V I am reading in one of the legs of C515, which is base of Q523.

By removing Q515 from the circuit, this -41V turns into milivolts.


Vbe in "removed Q515", measured from R525 and R535 is 1.3V which tells me that transistor is switched on and that's the reason I am having the wrong voltage above.
In addition, Vbe in Q513 is 0.2mV which tells me that that transistor is closed.


So, not sure if both transistors should be on and both voltages will make that in Q523,Q525 bases I would have +- 1.12V
Or......... both transistors should be off.......

Which part of the circuit should continue to investigate?????

[Francesc V.]

I've realized that I was checking voltages with transistors removed from the PCB.............so as long as transistors are in the PCB, voltages come to normal.

So it was normal to have +-30 V in the bases..........when final transistors are there, voltage decreases to +-1V