Use the following methods to judge the quality of electrolytic capacitors

Appearance inspection: Firstly, observe the appearance of the electrolytic capacitor. Good electrolytic capacitors usually have high glossiness, and the welding points have undergone anti-corrosion treatment without defects such as protrusions, indentations, or scratches. If the appearance of the capacitor is rough and there are obvious defects, it may be a low-quality capacitor

Internal resistance test: Using a DC meter for internal resistance testing can determine the quality of electrolytic capacitors. Generally speaking, when the internal resistance is less than or equal to 1 ohm, the quality of the capacitor is very good; When the internal resistance is between 1 and 3 ohms, the quality is good; When the internal resistance is between 3 and 10 ohms, the quality is acceptable; When the internal resistance is greater than 10 ohms, it indicates poor quality of the capacitor

Multimeter measurement: Use a multimeter to measure the capacitance and resistance values of electrolytic capacitors. After short circuiting the two pins of the capacitor and discharging it, connect the black probe of the multimeter to the positive terminal of the electrolytic capacitor and the red probe to the negative terminal. Normally, the pointer should first swing towards the direction of lower resistance, and then gradually return until it reaches infinity. The larger the swing amplitude or slower the return speed of the pointer, the larger the capacitance of the capacitor. If the needle does not change at a certain point in the middle, it indicates that the capacitor is leaking electricity; If the resistance reading is very small or zero, it indicates that the capacitor has broken down and short circuited

Signal generator observation: Input a sine wave signal through the signal generator and observe the frequency response of the electrolytic capacitor. If a capacitor exhibits stable response within the frequency range generated by the signal generator, its quality may be better.

Resistance test: Use the resistance range of a multimeter for measurement. Under normal circumstances, there will be a numerical display at the beginning of the measurement, and then it will slowly increase until the resistance value becomes larger (usually several hundred K Ω or more). If the displayed resistance value is consistently low, it indicates that there is almost a short circuit; If the displayed number remains above several hundred K Ω at the moment of measurement and remains almost unchanged, it indicates that the capacitor has deteriorated

Charge and discharge detection: Prepare a suitable power supply and a load resistor, connect the positive pole of the power supply to the positive pole of the capacitor, and connect the negative pole to one end of the load resistor. Observe the voltage change on the load resistance after connecting the power supply. If the voltage gradually increases and stabilizes at a certain value, it indicates that the capacitor is normal; If the voltage remains zero or fluctuates unstably, it indicates that the capacitor is damaged or has poor performance

Through the above methods, the quality of electrolytic capacitors can be effectively judged, ensuring the normal operation and safety of the circuit.