- CRT’s consist of a blown glass envelope, or shell, into which is placed a high voltage “gun” that sprays electrons onto the inside of the front surface, or screen. Chemicals (phosphors) on that screen convert the electron energy into light which you see as an image. In something like ninety five percent of the cases when a CRT fails, it is because the electronic gun has burned out. The repair consists of putting a new gun into the back, thus reusing the glass envelope and the expensive, finely tuned phosphors. The old gun can be repaired or disassembled. 
In 2004 I called up every potential CRT repair company I could think of. They all assured me that no one replaces guns any more. – PP