Pionner 2 chanel distortion on left channel

[ray9043]

Hi, today comes to me a Pioneer 2 channel, i dont have the model because the person who leave the amp dont leave the hetsink, only the board.

It has PW of 44z, the outputs are irf540 and irf9540.

Left channel distorted, right channel is OK.

I double check all caps and opamp, drivers transistors and everything is ok.

Im checking the pa2027a and i have this readings with 12.06V on B+ and GND.

PA2027a
pin1: 11.31
pin2: 8.98
pin3: 11.94
pin4: 11.96
pin5: 0.46
pin6: 0.0
pin7: 0.0
pin8: 0.0
pin9: 12.06
pin10: 0.03
pin11: 3.35
pin12: 0.27
pin13: 1.98
pin14: 4.64
pin15: 0.24
pin16: 0.02


I suspect the voltage on the pin 14 is to high.

 

[ray9043]

Sorry, i miss the picture

 

[Leolabs]

Have u try isolate the pre and power section,and swap channel to verify again?

 

[Perry Babin]

Contact the owner to get the model number.

 

[ray9043]

Hi!

the model is GM-X742, i download the service manual and im reading it.

I switch the channels and the distortion is in the same chanel, the left, so the problem is in the output section, i switch every transistor from side to side, caps, etc, double check resistor, the problem persists in the same chanel.

 

[Perry Babin]

If you remove the muting transistor, does the distortion remain?

 

[ray9043]

Where is it?

In the first picture is the left bad channel gate reading. The other is the clear sound channel. There is a remarkable diference.

 

[Perry Babin]

If you have a scope, follow the signal through the amp to see where the signal on the bad channel becomes distorted.