How to Test a Capacitor and Electrolytic Capacitor

Capacitors fail in several ways: capacitance can decrease, equivalent series resistance can rise, leakage can increase, or the component can become open or shorted. Electrolytic capacitors are especially affected by heat and age.

Inspect before measuring

Look for bulging, leakage, damaged sleeves and overheated board areas, but do not assume a visually normal capacitor is healthy. Many degraded capacitors show no external damage.

Discharge the capacitor safely

Remove power and confirm that stored voltage has been discharged using an appropriate method before connecting a meter. Large capacitors can retain dangerous energy after equipment is switched off.

Measure capacitance

If your meter supports capacitance measurement, compare the result with the rated value and tolerance. In-circuit components can influence the measurement, so isolation may be necessary.

Consider ESR

High ESR can cause ripple, unstable power rails, heating and startup problems even when measured capacitance appears reasonable. An ESR meter or suitable impedance measurement is often more informative for power-supply capacitors.

Verify the circuit symptom

After replacement, confirm that ripple, rail stability and the original fault have actually improved. Replacing capacitors without measurement can hide the real cause of a problem.