capacitor aging claim

Capacitors do age. And they age badly. That is no myth. In the world of those of us that collect CRT based devices, failing/limping electrolytic capacitors are a very common occurrence. I can't even begin to guess how many electrolytics I've replaced in terminals, monitors, and television sets. But, in these cases, small value electrolytics, the primary mode of failure is electrolyte loss. Your typical aluminum electrolytic is composed of two strips of aluminum foil - one side of one of these is coated in aluminum oxide. They're separated by an electrolyte soaked paper, and rolled up into a little can. The whole thing is "sealed" with a rubber plug crimped into the bottom. Over time, the seal is comporomized, and the electrolyte starts to deteriorate and evaporate, or sometimes leak out the bottom. If anything, use and heat will accellerate this. Since the electrolyte (which acts as part of one of the plates), starts to go away, the cap no longer works as it should, and the oxide layer starts to break down. Unroll a faulty thirty year old electrolytic, as well as a modern, still-good one. Compare. The older one will have a noticeably drier paper layer, and sometimes you'll see discolored marks on the oxide layer that look like pinholes. When a cap gets like that, no amount of "reforming" can bring back lost electrolyte. The ONLY time a capacitor can possibly reform, is if it is a high grade part, thoroughly sealed, and has not lost it's magic goo. The larger caps - large B+ filters, power supply filters, etc. Do seem to last longer, but I'm starting to see more and more of them failing in monitors. In Atari video games, a well known failure is the large (28,000uf, IIRC) power supply filter on the transformer block - affectionately known as the "big blue". This cap ages badly and fails often, and this is probably largely due to the fact that I'm sure Atari didn't buy the greatest parts in the world, coupled with the poor storage conditions most games faced. But, again, similar story - evaporated/destroyed electrolyte and damaged oxide layer. -Ian