Sound problem older Mitsubishi tv

I don't know if you're an electronics tech or not. Typically I've found on the old Mitsubishi's, that a small capacitor fries on the audio printed circuit board. If you are knowledgeable about these things, take the cover off, follow the speaker wires back, and
you'll probably find a burned capacitor close to where the speaker wires connect to the printed circuit board. If that's the case, you still won't know the value of the capacitor, because it'll be burned-up. Believe it or not, a lot of the manufacturers (but they only go back so many years), put their circuit schematics on-line for free.
If you don't know how to service electronics, I don't recommend trying this yourself.
A shop will fix it for under $100,... but your TV is not going to last much longer after that anyway,... so if I was you, I'd just get a new or used replacement TV. Used ones go for pretty cheap anymore.
If you've got a bad audio amplifier, it'll still cost you less than $100 at a TV shop,... but I wouldn't put that kind of money in a TV as old as yours.