Turn on tv and get full screen but after 5 minutes half the screen starts to scramble then goes blank leaving me with half ascreen

I would suspect your power supply deflection board is failing. Normally these tvs have a problem with the hyper board in which the image is scrambled and then clears up. Your problem is just the opposite and indicates a part is heating up on the power board. A good visual look at the board will be your best starting point. Look for burn marks, a capacitor that is rounded on top or leaking. Also look carefully to ensure your CRT bulbs have not leaked fluid onto one of the boards.

It's a starting point.