Irs...
3 basic.. but perhaps uncommon methods:
Isolate..
Reproduce...
Spec Check....
[/B]Most times, the issue, when I have pursued audio remedies turn out to be an "anomaly" caused by other factors; EX: poor/worn connection, poor/wrong interface with other components or external interference.
So... I use the I.R.S.... approach (my flow... :scratch2
Isolate or make sure the source of the issue IS the component and not cabling or the like. Source material should be considered as well.
Reproduce or try to make the unit do the same thing, malfunction under same/similar conditions. Often this narrows the section (as in an orchestra), that is causing the overall problem.
Finally, and this often proves to be most challenging, "spec check" the behavior of the section.. as most do have test points. Some basic technical and electrical knowledge does help. Get a "tech friend" if you don't like working with small stuff..
The challenge is getting a usable or relevant schematic. Here at AK, lots of folk have already worked through same/similar issues..., this helps a lot!