SA-610 Distortion - Pre-Amp problem?

I just aquired a SA-610 at a garage sale. I didnt really need it but for only $10 bucks I could not resist!

The amp powers up and all of the controls work properly. The problem is a large amount of distortion from both channels. It sounds like the input is being overdriven.

At low volume levels the distortion is not too noticable but once you get to about "3" on the volume knob the distortion increases.

The distortion is present in the headphone circuit as well as the speaker outputs. I have cleaned all of the switches and knobs but the problem remains.

I do have the schematics. I just need some suggestions on where I should look to isolate and repair the problem.

Thank you!

I've been doing a little more troubleshooting.

The distortion exist on both channels and on all inputs. It can be heard on both A & B speaker outputs and the headphone output.

Because the distortion exist on both channels I'm assuming that its being caused by one of the switches or the volume control. I have cleaned all of them several times but nothing has changed.

Do I have a bad switch/control or is the problem a component on the circuit board?

Here is a link to the Service Manual;

http://akdatabase.com/AKview/albums/userpics/10004/Pioneer SA610 Service Manual.pdf

Any help would be greatly appreciated.

Thanks!

One more bit of info;

With no audio signal going into the inputs I do not hear any distortion or excessive noise from the amplifier, even with the volume at maximum.

The distortion only occurs with an input signal.

I hope one of you guys can give me an idea what to test.

Thank you.

What input are you using?

grateful said:

What input are you using?

Click to expand...

I have tried all of the inputs, Tuner, CD Player, Turntable, Tape player etc. The distortion exist on all inputs regardless of the source.

They have a novel protection circuit. Check those components.

grateful said:

They have a novel protection circuit. Check those components.

Click to expand...

I thought the protection circuit was designed to protect the amplifier section from shorts and clipping. Does the audio signal pass through the protection circuit?

I was confusing that unit with another model. For a start check the bias of the output transistors. There should be .6 v on the base of each device. The audio signal passes through the relay. Tap it and see if it has an effect.