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Biggest source of failure in aluminum electrolytic caps is the rubber plug seal at the end of the aluminum can enclosing it.

The water-based chemistry inside the cap can last for a long time. A capacitor that has been on the shelf for 40 years in a proverbial cool,dry place may check perfectly okay. And if you see a bulge under the rubber, that's the pressure release valve. That part is already going bad. Yes, they fail from age even when not used. Eventually.

Heat is the enemy. Both from the surrounding circuitry and from heat the capacitor releases inside. The rubber end-plug hardens and shrinks. Eventually the seal is broken. The water-based chemistry inside literally dries up and the part breaks down.

Mileage and age both.

73

[QUOTE="nomadradio, post: 681548, member: 22"] Biggest source of failure in aluminum electrolytic caps is the rubber plug seal at the end of the aluminum can enclosing it. The water-based chemistry inside the cap can last for a long time. A capacitor that has been on the shelf for 40 years in a proverbial cool,dry place may check perfectly okay. And if you see a bulge under the rubber, that's the pressure release valve. That part is already going bad. Yes, they fail from age even when not used. Eventually. Heat is the enemy. Both from the surrounding circuitry and from heat the capacitor releases inside. The rubber end-plug hardens and shrinks. Eventually the seal is broken. The water-based chemistry inside literally dries up and the part breaks down. Mileage and age both. 73 [/QUOTE]

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