I am going to work on a pioneer receiver 1979 year. I have a variac, oscillscope, and two function generators.
I mostly repair vacuum tube amplifiers, and I have a B.S. in Electronics Engineering Technology.

Last time I tried to repair a receiver with this trouble I replaced both the stk0039, right and left. I was overzelous and replaced some other components that where not needing to be replaced by taking measurements of compomnents that where incorrect.

I also had to replace some jumpers which were not needing to be replaced. I learned my lesson the hard way.

I was wondering if there is a remedy to fix the one channel of the pioneer, and what steps I need to take to fix this problem.

 

First things to check are the speaker switches and relay in the output path. A very common fault is a dirty speaker protect relay.

 

What model is this? It would be beneficial if you went to audiokarma or elektrotanya and got a schematic for it before you begin. I also have a pioneer that had issues and a good cleaning with deoxit brought it back to life but not to say yours could be more or less.

 

https://www.hifiengine.com/ is also a good source for service and user manuals.