Here is where you are at in the troubleshooting.


It also illustrates the half-split technique. The remaining unknowns are in the shaded area. Not all components have an equal chance of causing your symptoms. You can either measure the output of the opamp or you can measure the C-E of transistor Q801 for a short.

 

Here is where you are at in the troubleshooting.


It also illustrates the half-split technique. The remaining unknowns are in the shaded area. Not all components have an equal chance of causing your symptoms. You can either measure the output of the opamp or you can measure the C-E of transistor Q801 for a short.



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So update I tested q801 not sure what readings I should be getting but comparing them to q802 which I take to be for the right channel the readings where around the same as for testing the op amp I’ve not done this as unsure of the process and the pins, don’t want to short anything out I know I would do this on D.C. volts on dmm, not sure where my black lead would go to the ground on casing of mixer or is there a ground on op amp then red lead inputs & output

 

Use the diode test of your DMM. the unit is not energized during that test. Disconnect whatever is connected to the master outputs

 

Use the diode test of your DMM. the unit is not energized during that test. Disconnect whatever is connected to the master outputs

It’s the op amp I was unsure of testing

 

How did you measure the two transistors? Voltage?

 

In your initial posting, you mentioned you heard a faint, distorted signal on the left channel.

That could be two possibilities .... cross-talk or the muting circuit is engaged.

The mute transistor is the transistor Q801.

You can check the output of the opamp on the AC scale and I suspect you should get over a half volt signal that is moving. If the circuit is muted, the collector of the transistor will not see that same AC Signal. If you don't want to measure it at the transistor, you can measure it on one side of R867.

If you don't know how to test the transistors using the DIODE test, your can find many examples out there. You may want to download the datasheet on that transistor so you can see how to identify the emitter, base, and collector.

I don't believe I asked you the model of your DMM.

 

A simple test you can do is press the mute button. Listen to the right channel. Does it sound like the left channel when you unmute the signal?

 

If you don't think you can do those tests .... here is a simple one

listen to it again, and note the levels in both ears. Press the mute button, if the right sounds like the left and the left sounds the same as before, then Q801 is defective. If the left goes quieter, the OpAmp will be suspect.

It would be easier if you had a tone generator.

 

If you don't think you can do those tests .... here is a simple one

listen to it again, and note the levels in both ears. Press the mute button, if the right sounds like the left and the left sounds the same as before, then Q801 is defective. If the left goes quieter, the OpAmp will be suspect.

It would be easier if you had a tone generator.

UPDATE:

Replaced op amp now i get sounds from the left channel as well as the right channel using the master balance, each side sounds the same, when set at mid point it’s much louder as it should be but the lights for both channels on the master volume only works when the master balance is turned to the right, when turned to centre point or to the left only the right channel light is working.

 

Ok ...

I'll assume you have all controls in the midway position, expecially any cross faders.

Now we have to track down a schematic of that section.

If you have a CD player connected to it, I would recommend you download some test tones, as they will be of a specific amplitude. then all you would have to do is play a track and measure the two outputs to be a little more descriptive than one channel is louder than another. A 15 to 30 second tone would be enough time to record the levels.