If you've got a heater to cathode short, there is no repairing by
conventional methods. Even a crt rejuvinator can't remove those shorts.
The only way to do it, and it's not always 100%, is to defeat the
heater line to the crt, meaning any path to chassis ground, and do a
wire wrap around the core of the flyback. You're creating a new heater
line free of the circuit ground. The cathode can short to the heater
all day long and won't make a difference.