Under normal circumstances, the quality of capacitors is mainly determined through observation, judgment, and the use of a multimeter. The observation method mainly refers to whether the capacitor leaks, bursts, or burns out. If the above situation occurs, the capacitor has been damaged.
1. Testing method for fixed capacitors
When measuring fixed capacitors below 0.01uf with a multimeter, due to their small capacity, only qualitative checks can be conducted to determine if the capacitor is leaking, if there is an internal short circuit or breakthrough. It is impossible to qualitatively judge its quality. In the measurement process, in order to ensure the accuracy of the measurement, a small resistor should be used first to discharge. Then select the RX10k range of the multimeter, use two pens to freely touch the two pins of the capacitor, and observe whether the multimeter pointer is deflected. Swap the probes and measure again.
Observe the changes in the hands of the watch. Under normal circumstances, the pointer should swing to the right and then slowly move to infinity. If the resistance value is small or zero, it indicates capacitor leakage damage or internal breakthrough; If the pointer swings from beginning to end, it indicates an internal circuit break in the capacitor.
For the detection of fixed capacitors below 0.01, the amplification effect of composite transistors can also be detected through additional circuits. Select two β with a penetration current less than 100 to form a composite circuit, as shown in the following figure.
Due to the amplification effect of the composite transistor, measure the charging of the capacitor. The discharge process will be amplified to increase the amplitude of the multimeter pointer for easier observation. Firstly, check if the capacitor is charged, and then determine its quality. Select the RX10k gear multimeter. Then connect the red and black pens of the multimeter to the emitter and collector of the composite tube. Observe whether the pointer can return to infinity after deflection. Then measure the exchange pen again. If one of the two cannot return to infinity, it proves that the capacitor is damaged.
When two probes respectively touch the two leads of the container, the probe first swings clockwise (to the right) (this process is the charging process of the capacitor), and then slowly returns to the left. When the pointer is stationary, the resistance value is the leakage resistance (R) of the capacitor. During the measurement process, if the pointer is far away from infinity, it indicates that the capacitor is severely leaking and cannot be used. When measuring the leakage resistance of some capacitors, if the pointer swings clockwise when it returns to the infinite position, it indicates that the capacitor leakage is more severe.
2. Detection method for fixed capacitors above 0.01uf
For fixed capacitors above 0.01uf, the RX10k range of the multimeter can be directly used to test whether the capacitor is charged, whether there is an internal short circuit or leakage. Firstly, discharge the capacitor to be tested, select the RX10k range of the multimeter, use two pens to touch the two pins of the capacitor at will, then observe the deflection of the multimeter pointer, and measure and exchange the probe again.
Observe the changes in the hands of the watch. Under normal circumstances, the two measuring hands should first swing clockwise (to the right) during the capacitor charging process, and then slowly return to infinity to the left. If the resistance value is small or zero, it indicates capacitor leakage damage or internal breakthrough; If the pointer does not swing from beginning to end, it indicates a circuit break between the two poles of the capacitor. According to the above inference, the capacitor is basically normal.
3. Check the quality of electrolytic capacitors.
The common problem with electrolytic capacitors is breakthrough leak. Capacity reduction or disappearance, etc. The performance of electrolytic capacitors can usually be judged by detecting their resistance.
The open circuit measurement steps for electrolytic capacitors are as follows:
(1) Firstly, use an electric soldering iron to remove the capacitor to be tested and clean the two pins of the capacitor.
(2) Check the appearance of the capacitor for any leaks Pin breakage indicates damage to the capacitor.
(3) Determine the polarity of the capacitor based on the pin length and capacitor side markings. As shown in the figure, the positive pin of a capacitor is usually longer, while the negative side is marked with one (negative).
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