1. To judge the polarity, first set the multimeter to 100 or 1K ohm, assuming that one pole is positive, let the black stylus connect with it, and the red stylus connect with the other pole, write down the resistance, then discharge the capacitor, that is, let the two poles contact, and then change the stylus to measure the resistance. The black stylus with large resistance is connected with the positive pole of the capacitor.

2. Adjust the multimeter to the appropriate ohm gear. The principle of gear selection is: 20K gear for 1μF capacitor, 2K gear for 1-100μ f capacitor, and 200 gear for capacitors larger than 100 μ f..

3. Then use the red pen of DT2201D multimeter to connect the positive pole of the capacitor and the black pen to connect the negative pole of the capacitor. If the display increases slowly from 0, the capacitor will be normal if the overflow symbol 1 is displayed at last. If it is always displayed as 0, the capacitor will be short-circuited. If it is always displayed as 1, the capacitor will be open.

1. Detect small capacitance below 10pF.
Because the capacity of the fixed capacitor below 10pF is too small, it can only be qualitatively checked for leakage, internal short circuit or breakdown when measured by multimeter. When measuring, you can choose to use the multimeter R×10k, and use two probes to connect the two pins of the capacitor at will, and the resistance should be infinite. If the measured resistance (the pointer swings to the right) is zero, it indicates that the capacitor is damaged by leakage or internal breakdown.

2. detect the fixed capacitor of 10PF-0.01μF f.
Detect whether the fixed capacitor of 10pf ~ 0.01μ f is charged, and then judge whether it is good or bad. The multimeter can choose R×1k gear, and the values of both transistors are above 100, and the penetration current is small. Silicon triodes of 3DG6 and other models can be selected to form composite pipes. The red and black probes of the multimeter are respectively connected with the emitter E and collector C of the composite pipe. Due to the amplification effect of the compound triode, the charging and discharging process of the measured capacitor is amplified, which makes the pointer swing of the multimeter increase, thus facilitating observation. It should be noted that in the test operation, especially when measuring the capacitance with small capacity, it is necessary to repeatedly exchange the contact points A and B of the measured capacitance pin, so as to obviously see the swing of the multimeter pointer.

3. Detect the fixed capacitance above 0.01μF f.
To detect the fixed capacitance above 0.01μF, the R×10k gear of multimeter can be used to directly test whether the capacitor has charging process and internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.