Marantz SR-940, Tape ON/OFF not working, help please!

[SAS73]

Hello friends ,
Trying to troubleshoot Marantz SR940 receiver.
Tape ON/OFF function is not working.
Can somebody explain how this schematic works ?
What I understand is when Tape ON/OFF switch is pressed I should have 14 volts go to D515 and D516, and then transistors Q517 and Q516
should send 14 volts to electronics function switch TC9151 pins 19 or 20.
Pin 19 tape is ON, Pin 20 Tape is OFF.
This not happening no flipping voltages from Q517 or Q516, checked transistors and diodes , they are ok.
Any Ideas ?
Help please !

[David_AVD]

Have you checked that the switch itself works?

Do you have a link to a pdf copy of the service manual? Too hard to trace with the fragments posted.

[SAS73]

Thanks David ,
Yes I checked, switch itself is working correctly.
Here is a link for the service manual
https://easyupload.io/d4c75c

[David_AVD]

This is typical of Marantz making circuits much more complicated than they need be.

It looks like the button goes through C510 which would make the press into a pulse, not a steady state.

I haven't looked much beyond that, but I'm sure I've had to replace a TC9151 before due to it doing weird things on some input selects.

[SAS73]

Thanks David!
Replaced TC9151P, same issue, injected 12 volts from external P/S to pin 19 , it`s mutes FM radio and Tape source is playing  (so it`working from external P/S)
The best I can understand it`s when I press TAPE btn it`s charging C510 to 14 volts, but then I am lost , I don't understand how Q516 , Q515 is switching ?
The switching signal goes to emitter ?
This is bugging me !
Help please!
P.S. IS THIS A FLIP FLOP circuit ?
 
 

[SAS73]

UPDATE
After hours of troubleshooting, gave up, assembled the flip flop circuit (couple of transistors and miniature relay)
Bypassed the original TAPE select circuitry, and it's working now!
Still don't understand, what is "wrong" with the original circuit.
 

[David_AVD]

Like I said, Marantz often have some weird arse circuitry that's sometimes hard to decipher. lol

It is probably some sort of flip flop, with with way more components than anyone else would use.

[SAS73]

Yep. You are right about Marantz, but it`s sounds amazing !