Compare the readings of the output and driver transistors on one channel to the corresponding transistors on the other channel. Measure the resistance from leg 1-2, 1-3 and 2-3, using the same probe placement on both channels. Is there any difference?
No difference, same situation.
I have found difference on last op-amp output, without input signal, strange on pin1, pin7 is ok. What do you think? Measure in attached
Attachments
Pin1 -0,39V
Pin2 -0,003V
Pin3 -0,003V
Pin4 -14,62V
Pin5 -0,003V
Pin6 0V
Pin7 +0,07V
Pin8 +15,22V
The op-amp looks OK. There is a 2.7 ohm resistor connecting pins 1 and 7 to the center of the string of 4 diodes.
Lift those and see if either channel drives DC to their output transistor collectors.
Lift those and see if either channel drives DC to their output transistor collectors.
Shorting the muting transistor should have blocked any noise that originated before it. Lifting the 2.7 ohm resistor should eliminate everything after it if there is no DC on the output of either channel. The op-amp looked healthy but you might try replacing it.
i have shorted both muting transistor but pop was present. with lifting the 2,7ohm pop is deleted.
you mean the last op-amp?
I have changed last op-amp but the problem is already present. I have changed also muting fet but don't solve the problem
Only 1000uf 25V leaked ( picture in attached). I have recapped all electrolityc capacitors with a new capacitors
Attachments
I have checked mute jfet position on circuit, this fets are on last op-amp inputs, so the problem should be on the op-amp output
Set your scope to DC coupling, 2ms and 1v/div and rub the tip of the probe around on the board. It should not deflect any unless you scratch through the solder mask. Check around all capacitors.