Electrolytic capacitors may fail due to excessive discharge or depletion of electrolyte and failure to charge. The following is the method to judge the quality of the capacitor:

1. Multimeter method to check the quality of the capacitor
This is the most common method
Put the switch of the multimeter on the R×10kΩ or R×1kΩ electrical barrier, connect the black lead to the positive terminal of the capacitor, and the red lead to the negative terminal of the capacitor (non-polarized capacitors can be connected at will), and observe the swing of the needle , That is, the capacitor can be judged roughly

• The pointer swings quickly to 0Ω first, and then slowly returns to the position of hundreds of kΩ and then stops, indicating that the capacitor is intact
•  The pointer does not move, indicating that the capacitor has been damaged, that is, open circuit
•  The pointer swings to 0Ω and does not return, indicating that the capacitor has been broken down
• The pointer swings to 0Ω, and then slowly returns to a smaller resistance value and then stops, indicating that the leakage current of the capacitor is large, and you can decide whether to replace the capacitor according to the specific situation.

2. Charge and discharge method
If you can’t find a multimeter, you can use this method
You can connect the capacitor to a DC power supply of 3-9V, the time is about 21s
Remove the capacitor and short-circuit the two ends of the capacitor with a wire. If you hear a “pop” discharge sound, or see a spark, it means the capacitor is good, otherwise it means the capacitor is bad
If the capacitor is an electrolytic capacitor, the positive terminal of the power supply is connected to the “+” polarity terminal of the capacitor

3. Determination of the electric quantity of the capacitor
Generally, the capacitance of the capacitor is measured by a dedicated bridge, or it can be measured by voltammetry. After the power is turned on, the reading on the meter should be read as soon as possible. Then the capacitance C of the capacitor is in the formula: C is the measured Capacitance of capacitor, μF; I is ammeter reading, A; U is voltage reading, V

The above are several the method to judge the quality of the capacitor.