How to Use a Multimeter to Detect Capacitors
(1) Detection of fixed capacitors with a capacitance above 0.01 pF: Adjust the pointer-type multimeter to the R×10k ohm range, and perform ohm zero adjustment. Then, touch the two pins of the capacitor with the red and black test leads of the multimeter respectively, and observe the change of the pointer of the multimeter, as shown in Figure 1. If, at the moment when the test leads are connected, the pointer of the multimeter swings slightly to the right and then returns to infinity, and when the test leads are swapped and the measurement is carried out again, the pointer swings to the right and then returns to infinity, it can be judged that the capacitor is normal; if, at the moment when the test leads are connected, the pointer of the multimeter swings to near "0", it can be judged that the capacitor is broken down or seriously leaking; if, at the moment when the test leads are connected, the pointer swings and does not return to infinity, it can be judged that the capacitor is leaking; if the pointer of the multimeter does not swing twice, it can be judged that the capacitor is open-circuited.
(2) Detection of fixed capacitors with a capacitance less than 0.01 pF: When detecting small capacitors with a capacitance below 10 pF, due to the too small capacitance, when measured with a multimeter, only the leakage, internal short circuit or breakdown of the capacitor can be checked. When measuring, select the R×10k range of the multimeter, and connect the two test leads to the two pins of the capacitor arbitrarily. The resistance value should be infinity. If the measured resistance value is zero, it can be determined that the capacitor is damaged due to leakage or internally broken down.
(3) The following method can be used to detect fixed capacitors with a capacitance between 10 pF and 0.01 μF. Adjust the multimeter to the R×10k range, and select two transistors 3DC6 (or 9013) with a β value greater than 100 to form a composite transistor, and its circuit schematic diagram is shown in Figure 2. Utilize the amplification effect of the composite transistor to amplify the charging current of the capacitor under test, so as to increase the swing amplitude of the pointer of the multimeter. Connect the capacitor under test between the base b and the collector c of the composite transistor, and connect the red and black test leads of the multimeter to the emitter e and the collector c of the composite transistor respectively. If the pointer of the multimeter swings slightly and then returns to infinity, it indicates that the capacitor is normal; if the pointer does not move or cannot return to infinity, it indicates that the capacitor is damaged. During the test operation, especially when measuring capacitors with a small capacitance, repeatedly swap the contact points of the pins of the capacitor under test to clearly see the swing of the pointer of the multimeter.
