Question Stereo sound acting up a bit

[Daak12]

I have the weirdest issue with a home theater receiver I brought out of storage after a decade.
Its a Sony STR DE-915.

I will turn it on and after about 10 min, the high frequencies on the front left channel will fade in and out for 30 sec then fade out permanently while the system is on. It will still have sound but it will be lower frequencies and maybe at lower volumes also. If I turn the stereo off and on again, the problem doesnt happen again (while the system is still warm). So the issue happens every time the receiver warms up. This never happened when I used the receiver a a decade or so ago. Its more of an irritation thing that I would like to fix if anyone knows whats going on. I dont mind soldering new parts in if it comes to that.

Troubleshooing ive done:
-Its not the speaker
-Its not the speaker wire
-Its not the audio source
-Its not the connector on the receiver (speaker set B does the same thing)
-I dont think its dust because I recently dusted the interior out
-I tried all kinds of different sound modes and stereo only. subwoofer and no subwoofer - issue happens every time
-I tried plugging into different outlets

I just dont know what would cause the high frequencies only to fail on a speaker channel. Any help?

 

[Daak12]

No one answered so I found the answer myself. Maybe it will help someone.

Capacitors are used in the audiostream of a receiver. Big caps for bass and smaller caps for high range. Over time caps go bad - the electrolyte inside leaks out or the membranes degrade. If you can determine which cap is bad, it can be replaced with soldering skills but be ready for other caps to fail also. Caps like to be used so its better to fire up anything with larger caps every month or so to get the most life.

Aftermath: Im too lazy to figure out which cap it is right now but if I turn the receiver on its side the fade out/in of highs might occur once while warming up but quickly goes away on its own. I never need to turn it off and on again. Im hoping the problem goes away by itself with daily use of receiver. We'll see.