Electrolytic capacitor disease
A basic multimeter capacitance reading can look normal on a failed capacitor. Equivalent series resistance is the number that tells the truth.
24 October 2026 · 4 min read
Related from the bench
As electrolytic capacitors age, their electrolyte dries out and their internal resistance — ESR — rises. A capacitor can still measure close to its rated capacitance while its ESR has climbed high enough that it can't filter or smooth a supply.
Use an ESR meter or LCR meter, ideally with the capacitor out of circuit. Compare to datasheet values for that capacitance and voltage — and on an old cluster, when one is bad, its neighbours usually aren't far behind.
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