Zenith CCII 25GC45 Oil Cap overheating

[wb2mep]

This is one of the vertical chassis sets with the constant-voltage (ferroresonant) power transformer and oil-filled motor-run capacitor. A few years ago the set would trip its circuit breaker after being on for a while. After a couple of resets, it eventually would trip as soon as you turned it on. I replaced that oil-filled cap with one from an even older CCII I had parted out (23", bad CRT) and all was well.

The set was kept in the garage and didn't get much use after the DTV transition, but I would turn it on every now and then to wake up the CRT and reform the 'lytics.

Last year we moved the set to the back patio and it started the breaker-tripping after warming up again. It would run a couple hours before tripping the breaker, and would always come back after the set cooled down. Last week, I tried replacing that oil-filled capacitor again, as the symptoms were the same as the first time it failed, and I had a N.O.S. (1976 date code) replacement. I left the set running with the new cap, and went in the house for a few hours, and came back and found the set off with a tripped breaker again.

So I set my DMM to monitor AC line current. From a cold start, the set was drawing 1.07 amps. It held steady for about 2 hours, then started creeping upwards. That oil capacitor was heating up. It was too hot to touch when the line current reached 1.3 amps, and the breaker tripped at 3.1 amps.

Is it possible that a N.O.S. oil-filled capacitor could have the same failure mode as a well-used one? I didn't think they had shelf-life issues like electrolytics. This capacitor is connected directly across the secondary of the power transformer. Is there any kind of fault in the set itself that could cause that cap to heat up? Thi pic & sound are good until the breaker trips.