restorer-john
Grand Contributor
The tricky thing with analyses of this sort is with how you can be certain that the root cause you've identified is the true root cause, and not something that has happened as a result of something else that you didn't think would be be the root cause, because it didn't occur to you. A younger sister of mine once told me about the engine failure of the car she owned. Apparently there were a bunch of similar failures of the same engine in that particular brand of highly regarded Japanese car. Anyway, as she explained it, the head warped, which caused the engine to overheat. I asked her how she had determined that it wasn't the other way around, i.e., that the reason the head warped was because it got hotter than it was supposed to get, and that the root cause was something else, that had caused (or allowed) the engine to overheat. She insisted that the head warped first and this caused the engine to overheat. This is what some mechanic had told her. She is not a mechanically minded person in the least.
I first ran into these capacitor failures maybe 25-30 years ago. Even unused new old stock capacitors of this type develop micro cracks in the epoxy which, of course, pours cold water on your doubts as to the root cause. The difference of course is they are not subject to 120V/240V AC continuous across the capacitor, with no reactive impedance current flow and zero heating. So they clearly do not explode.
I'll dig out some NOS caps of this type with such cracks if I get a chance (and haven't thrown them out).