How to use a multimeter to determine the quality of a capacitor

　　Depending on the capacity of the electrolytic capacitor, the R×10, R×100, and R×1K ranges of the multimeter are usually selected for testing and judgment. The red and black test leads are connected to the negative pole of the capacitor respectively (the capacitor needs to be discharged before each test), and the quality of the capacitor is judged by the deflection of the needle. If the needle swings up quickly to the right and then slowly returns to its original position to the left, the capacitor is generally good. If the needle does not turn back after swinging up, it means that the capacitor has broken down. If the needle gradually returns to a certain position after swinging up, it means that the capacitor has leaked. If the needle cannot swing up, it means that the electrolyte of the capacitor has dried up and lost capacity.

　　Some capacitors with leakage are not easy to accurately judge whether they are good or bad using the above method. When the withstand voltage of the capacitor is greater than the battery voltage in the multimeter, according to the characteristics of electrolytic capacitors that the leakage current is small when forward charging and large when reverse charging, the R×10K block can be used to reverse charge the capacitor and observe whether the position where the needle stays is stable (that is, whether the reverse leakage current is constant). The quality of the capacitor can be judged with high accuracy. The black test pen is connected to the negative pole of the capacitor, and the red test pen is connected to the positive pole of the capacitor. The needle quickly swings up and then gradually retreats to a certain place and stays still. This means that the capacitor is good. Any capacitor whose needle stays unsteadily at a certain position or gradually moves to the right after staying has leakage and cannot be used anymore. The needle generally stays and stabilizes within the 50-200K scale range.