replaced Q47 with the original- no difference
I have tried to draw the circuit of the other two transistors (Q40 and Q41) not shown on the circuit.
Q40 is a 2SC2378 and Q41 is a 2SA954- both test good.
The voltages on each are:
Q40 e 0/ b 4v/c 0v
Q41 e 65.7 /b 65.7 /c 0
Q39 e 0 /c 2.2 rises to 4. then back to 2.2 etc /b 0 rises to .3 then back to 0
This really has me very confused
any help appreciated
I have tried to draw the circuit of the other two transistors (Q40 and Q41) not shown on the circuit.
Q40 is a 2SC2378 and Q41 is a 2SA954- both test good.
The voltages on each are:
Q40 e 0/ b 4v/c 0v
Q41 e 65.7 /b 65.7 /c 0
Q39 e 0 /c 2.2 rises to 4. then back to 2.2 etc /b 0 rises to .3 then back to 0
This really has me very confused
any help appreciated
Attachments
Thanks, completely understandable. Those 2 transistors are in play so need clear understanding, will look at figs a bit later.
Could you post a hi-res pix of this area including Q39-Q44, include both track and component side
Last edited:
Suggest measure Q40, 41 b/c/e voltages to GND on the working unit.
Looking at the interwork of those transistors
The "speaker line" (Q25c...) should normally be low, less than +/-50mV.
That feeds into Rxxx and Q41b (not included in my pix so can't confirm).
Q41e(pnp) is fed by R102 and also connects to Q39c, Q42e rail. When Q41
turns on, voltage on Q41c will turn Q40 on and drag that Q39c/Q42e
rail down, so the Q41e voltage will fall and Q41 may turn off, so you
might get some cycling.
When Q39c/Q42e rail is dragged down would expect Q43,44 to turn off
then Q45 turns off so speaker relay releases. Voltage at Q43c goes to
near 71V rails voltage causing Q46, 47 to be incorrectly biased/turn
off so NFB relay releases.
Grateful if someone would correct me.
I would expect Q41 to be normally on
Looking at the interwork of those transistors
The "speaker line" (Q25c...) should normally be low, less than +/-50mV.
That feeds into Rxxx and Q41b (not included in my pix so can't confirm).
Q41e(pnp) is fed by R102 and also connects to Q39c, Q42e rail. When Q41
turns on, voltage on Q41c will turn Q40 on and drag that Q39c/Q42e
rail down, so the Q41e voltage will fall and Q41 may turn off, so you
might get some cycling.
When Q39c/Q42e rail is dragged down would expect Q43,44 to turn off
then Q45 turns off so speaker relay releases. Voltage at Q43c goes to
near 71V rails voltage causing Q46, 47 to be incorrectly biased/turn
off so NFB relay releases.
Grateful if someone would correct me.
I would expect Q41 to be normally on
It seems that Q43b being 1.2v is the key to turning on the relay coil drive circuits, as this appears to turn on both the NFB and spkr relay. I measured the speaker relay and it also is not getting coil voltage.
Q43b goes between 0.5v and 1.05v, and I think is not holding long enough for the timing circuits to charge and thus for the coil voltage to flow.
I pulled Q45- tests good, and replaced D34.
Unfortunately now the amp is now not even turning on- so I am thinking there could be a broken wire somewhere- all the AC fuses test good, so I will go hunting
Thanks again for reading and helping
Q43b goes between 0.5v and 1.05v, and I think is not holding long enough for the timing circuits to charge and thus for the coil voltage to flow.
I pulled Q45- tests good, and replaced D34.
Unfortunately now the amp is now not even turning on- so I am thinking there could be a broken wire somewhere- all the AC fuses test good, so I will go hunting
Thanks again for reading and helping