Methods and Procedures for Testing Capacitor Quality with a Multimeter
Fixed capacitors below 10pF have an extremely small capacitance value. When measured with a multimeter, only qualitative inspection can be performed to check for leakage, internal short circuit or breakdown.
For measurement, select the multimeter's R×10k range. Connect the two test leads arbitrarily to the two pins of the capacitor. The resistance reading should be infinite. If the measured resistance (the pointer swings to the right) reads zero, the capacitor has leakage damage or internal breakdown.
2. Testing fixed capacitors of 10PF ~ 0.01μF
To test whether a fixed capacitor of 10pF ~ 0.01μF can be charged and judge its quality, set the multimeter to the R×1k range. Use two triodes with a beta (β) value above 100 and low leakage current.
Silicon triodes such as 3DG6 can be used to form a composite transistor. Connect the red and black test leads of the multimeter to the emitter (e) and collector (c) of the composite transistor respectively.
Due to the amplification effect of the composite triode, the charging and discharging process of the capacitor under test is amplified, which increases the swing amplitude of the multimeter pointer for easy observation.
Note: During testing, especially for small-capacity capacitors, repeatedly swap the capacitor pins to contact points A and B to clearly observe the deflection of the multimeter pointer.
3. Testing fixed capacitors above 0.01μF
For fixed capacitors above 0.01μF, use the multimeter R×10k range to directly test the capacitor for charging, internal short circuit or leakage. The capacitance can be estimated according to the amplitude of the pointer's right deflection.
Steps to Test Capacitor Quality with a Digital Multimeter
① Determine polarity: First set the multimeter to the 100 or 1k ohm range. Assume one terminal is the positive pole, connect the black test lead to it and the red test lead to the other terminal, then record the resistance value. Discharge the capacitor by shorting its two terminals, then swap the test leads and measure resistance again. The terminal connected by the black test lead in the measurement with the larger resistance value is the capacitor's positive pole.
② Set the multimeter to an appropriate ohm range. Range selection rule: use the 20k range for 1μF capacitors, the 2k range for capacitors from 1μF to 100μF, and the 200 range for capacitors larger than 100μF.
③ Connect the red test lead of the multimeter to the positive pole of the capacitor and the black test lead to the negative pole. If the reading rises slowly from 0 and finally shows the overflow symbol "1", the capacitor is normal. If it always shows 0, the capacitor has an internal short circuit. If it always shows "1", the capacitor has an internal open circuit.
