721-TS Problems

[bgadow]

While waiting for parts/schematics for some other projects I pulled this set out after a long hiatus. It has been recapped & many resistors have been checked. It has 2 major problems:

1) No vertical sweep. A capacitor between the 6SN7 grid & filament fills the screen nicely. The osc.xsfmr. checked okay when I last had it out but I was reading somewhere else about leakage across the windings (?). Quick & dirty substitution of some others I have (not the correct xsfmrs) changed nothing.

2) C4 is a 2-section low voltage cap that I replaced previously. I sometimes leave those types alone but this one was beginning to "puke" out the bottom. In running the set the other day I started to smell something and looked down to see C4A bulging just like the can of soup on the stove in some old bw short I've seen. (Stooges?) Anyway, I shut it down, that cap was an older stock so I swapped it, the newer one did the same thing, got very hot and finally popped. Closer examination showed that C4B may have already died so I changed them both, now it is C4B that gets hot. I have triple-checked the connections, C3A, 80mfd, had been replaced but I tried subbing it again just for the heck of it, no help. I pulled the big power resistors on the back out of circuit and they all checked okay. (more to come...)