I had an Apex AT2708S that had sound but no picture. There was a bulging capacitor, C450, that I replaced but that didn't fix it. After I downloaded the schematic for free, I did some measuring. The problem was a bad solder joint on the socket connector on the neck of the CRT. The heater contact needed to be resoldered. It was a cheap fix.
You gotta love cold solder joints. Thanks for sharing the repair. Do you remember what pin number it was or was it even marked?
There were 2 pins marked with an H. I resoldered all the pins since I was there. I was glad I didn't need to buy a flyback for it.