Technics SE-A900S no relay click

[glenn jarrett]

I have been asked to have a look at a friends amp
the amp powers on and the vu meters light up but no speaker relay click
the operation light is not lit
you can hear the big power relay click on and off
the main power supply is working both caps test ok
i have had the board out and checked all the caps replaced two which where out of spec
replaced caps C502 / C504 100uf 6.3v and R502 which was burnt
put it back together and still the same but when switched on R502 gets very hot
i have included the manual
https://www.manualslib.com/manual/387765/Technics-Se-A900s.html?page=1#manual
20200716_152600 by glenn jarrett, on Flickr

20200718_153233 by glenn jarrett, on Flickr

 

[a.palfreyman]

According to the circuit diagram the resistor connects the common emitters of Q454 and Q456 at 0v to pin 13 of IC 501 ( power amp module) which should also be 0v. You would need at least 40v dc across this resistor to develop 0.5W so the 50v dc supply would be enough to overheat it. Was the correct value fitted (3k6) if I read it properly? If so can you check the voltage across it and also the voltages of both ends relative to earth. If pin 13 end of the resistor is at 50v then it looks like the module might have gone.

 

[Mark65]

For anyone looking R502 is on page 17 of the schematic.
R502 has a complementary component R501, may be worth measuring the voltages around these resistors to workout if the problem is up or downstream of R502
There are some voltages marked on the diagram and these may give some clues