My own Sharp CRT TV was not getting any sound on channels 4 or 5.
At first I suspected the cable box was the problem.
I run the cable directly into the TV set and turn on the TV and to my surprise there was still no sound on channels 4 or 5.
I next hooked up a DVD player to the TV and again no sound on channels 4 and 5.
By now I am sure there is a problem with the TV and not the source of video/audio.
I take apart the TV and use some compressed air to blow out any dust build up.
I start to inspect the board and right away I see some bad solder joints so i reflowed several solder joints. I tested the TV and no sound on channels 4 and 5
Now I move on to testing the electrolytic capacitors on the board. Around the audio IC and I find 2 e-caps with higher esr. They were 330uf@16v. The ESR was around .60, I said to myself here is the problem. I replaced the caps with 2 new ones and the ESR is .16. I put it together enough to test and when I turned on the TV still NO SOUND.
I check some other on board resistors, diodes, etc and all seemed to be good.
I got a service manual for the model of TV. One of the things it recommends to do was to set everything to factory defaults before following any service work.
I turned on the TV in service mode and held down both volume + and – at the same time for more than 2 seconds and the TV turned off by itself.
I turned on the TV and noticed the brightness and color were different so I knew it set everything back to default at this point.
Funny thing is I already had the TV set to channel 3 from before while testing, and suddenly noticed the TV had sound.
It seems to me there was something corrupted on the IC and once all the original default values were set back to original all was well.