1. Judge the quality of the capacitor based on its capacitance.

If the measured capacitance is significantly less than the nominal value, it means that the capacitor is broken. Generally, if an electrolytic capacitor is left for a long time, the internal electrolyte will dry up, causing its capacity to become very small. This kind of capacitor is generally not suitable for use. If the multimeter displays a reading of "1" when actually measuring a capacitor, which means it overflows, you can use the multimeter's resistance range to measure its resistance. If the displayed resistance is very small, it means that the capacitor has broken down and been damaged. If the measured capacity of a certain capacitor is much larger than the nominal value, it means that the capacitor has a large leakage current, and generally this capacitor should not be used.

2. Measurement of capacitor leakage current

When measuring leakage current, connect the measured capacitor in series to a DC ammeter (you can use the 20mA range of a digital multimeter to measure), and then connect it to a 5V DC power supply. At first, the current displayed by the ammeter is larger, and then gradually decreases until it approaches 0. Assume that after the capacitor is fully charged, the current displayed by the ammeter is not 0, indicating that the capacitor is leaking. At this time, the current displayed by the multimeter is the leakage current of the capacitor.