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A cheap component tester with ESR function.

The simplest reliable method of testing an electrolytic capacitor is with an ESR (Equivalent Series Resistance) tester. A basic one with a graphical display but without a case is available very cheaply from Far Eastern sellers. This is an excellent investment as it will also identify and test many other types of component. A good electrolytic capacitor should show an ESR of a fraction of an ohm, and a vloss (another measure given by these testers) of a fraction of a percent.