tv screen is half-black

Could be something to do with the ariel signals?

This happened to me once. It had something to do with a tube something-or-other needing replacement due to age. Banging on it may or may not have helped (though it was fun); I was quoted a repair fee of around $80 in the sears electronic department and ended up just getting rid of the thing.

I wish I had better news.

Boy, did I wail on that sucker...

Sounds like the upper deflection coils have gone.
It's either the coils themselves or it's the drive circuitry.
If it's the drive circuits they can be repaired and it should be easy to spot but if it's the coils then it's a new tube.
Itd be cheaper to go and buy a new telly than replace the tube assuming you could even get one of course.