If it is a newer one, it is possibly a weak CRT. Alot of the last CRT TVs o ut there had AKB which is Automatic Kine bias which adjusts the greyscale c ontinuously. This allowed them to use crappy CRTs and have the set be unwat chable after they got to a certain point of weakness. This would necessitat e the purchase of another set, which is their goal.
You could try wrapping the fly, which means to put a inding around the core to substitute the filament supply to the cRT but a higher viltage. this is the same thing as putting a brightener on it in the old days. There should be some instructions on the net somewhere. You'll need some wire, a razor knife and a soldering iron and solder.
It doesn't always work, and soetimes induces an interelectrode short oin th e CRT, but you probably got nothing to lose. These days, CRT TVs are worth about five bucks if they work well. Some really nice vintage models more, b ut that ain't what you got.
Really, if you got a car, look on Craigslst in "free". They are giving away $3,000 HD home theater projection TVs these days. And I mean working. That 's why I don't work on TVs anymore.
If you are out to learnelectronics, that particular unit is not the best th ing in the world to start on, audio equipment would be better. Get you a us ed scope off eBay or something if you really want an education. A CRO, (cat hode ray) not an LCD.
Actually, TVs have become almost ipossible to service. Some of them don't j ust blank the picture if the CRT is weak, they go into protection and you h ave to unplug them to get it back. The manufacturers really stuck it to peo ple. I wouldn't give a dollar for any TV built within the last two decades. I was going to restore my vintage Sony XBR (KPR36XBR) built in 1989 which sold for two grand new, but I blew that off. And let me tellya, I would pit the picture on that thing with anything when working properly. No HD neede d, it was that sharp. If any TV of that era could be called a collector's i tem that would be it.
But it went out to the curb last year. Still have a good blue CRT for it on Craigslist. No bites.