fli amp not producing audio

[rrae]

When amp turn's on, there is no audio.
No shorted fets or output transistors. I had bounch of 4558 and 494 so i replaced them. I get -/+ 15v on opamps. I got -/+ rail voltage on center of output transistors.
I guess there is no schematic or service manual for this amp.
494
1 2.14
2 2.87
3 0.07
4 0.10
5 1.39
6 3.60
7 0.01
8 12.5
9 2.45
10 2.86
11 4.9
12 4.9
13 11.92
14 12.50
15 4.40
16 4.40
I am not sure what am i missing.

 

[Osvaldo de Banfield]

Do you have an oscilloscope? Do you know to use it?

 

[rrae]

I dont have in this country where i am living.

 

[Osvaldo de Banfield]

Then OK, let´s suppose the inverter is working. Which is the voltage across drain/collector f output devices? And gate/base? Measure it with respect to emitter/source, not to gnd.

 

[rrae]

weird thing, if my psu voltage is about 12v - get low disorted output, if i reduce the psu voltage under 10v, i can get higher output volume, but still disorted.

 

[Perry Babin]

Post a photo of the audio board.

 

[rrae]

Here You go

 

[Perry Babin]

Post one of the bottom of the other board, specifically, the half of the board used for audio.

 

[rrae]

Here it is

 

[Perry Babin]

If you drive a sine wave into the amp, do you read significant DC voltage on the center pin of the connector near C22?

 

[rrae]

No, sir. Drove 40Hz sin wave, got nothing special - 0.14 and changing to 0.01 VDC

 

[Perry Babin]

Do you have positive and negative supply voltage on the power supply pins of the op-amps on the preamp board?

 

[Osvaldo de Banfield]

Ok, but I still don´t know if the output devices are biased.

 

[Perry Babin]

I'm sorry. That should have been AC voltage on the center pin.