Sounds like one or more of the crts is shorting. During startup go to the Screen Controls and try turning the green down a tiny bit at a time until the set stays on. You may have to play with the red & blue too. Now with the set on, take the handle end of a screwdriver and tap on the neck of each tube. They are glass so don't tap too hard! Also watch out for HIGH VOLTAGE in there! If you see bright flashes of color on the screen while tapping then that crt is going, going, gone.
Hammer
Hammer