Verifying the Functional Condition of Resistors, Capacitors, Diodes, and Bipolar Junction Transistors Using a Multimeter
1. The fault of resistor (R) is that the actual resistance value does not match the nominal resistance value. Therefore, a multimeter ohm can be used to measure the quality of the resistor. Usually, the fault of a resistor is an open circuit (measured by a multimeter with an infinite resistance value), and the fault of a resistor short circuit is extremely rare.
2. The common faults of capacitors (C) can generally be classified into two types: breakdown (short circuit and leakage caused by some reason on the two plates of the capacitor (the insulation resistance of the capacitor is less than normal), and open circuit (the internal leads of the capacitor are disconnected from the plates, and the capacitor has no capacity) and failure (the capacity of the capacitor is less than normal).
Measurement of capacitor leakage and breakdown: Set the multimeter to the X 10K position (use the X 1K position when measuring electrolytic capacitors), and during the measurement, the multimeter pointer first swings to the ground in the direction where R is zero, and then retracts to the direction where R is infinite. After the pointer stabilizes, the resistance value indicated is the insulation resistance of the capacitor (for electrolytic capacitors, the black probe of the multimeter must be connected to the positive terminal of the electrolytic capacitor).
Experimental results have shown that the insulation resistance of electrolytic capacitors should generally be several hundred kiloohms or more, while the insulation resistance of other capacitors should be several tens of megaohms or more. If the insulation resistance is less than the above value, it indicates that the leakage of the capacitor is not suitable for use. The smaller the insulation resistance, the more severe the leakage. If the insulation resistance is zero, it indicates that the capacitor has been broken down.
3. The main characteristics of a diode (D) are its unidirectional conductivity. A multimeter should measure a certain resistance value in the forward direction and infinity in the reverse direction. If a resistance value is measured in the reverse direction, it indicates that the diode has been damaged.
4. The transistor (Q) consists of two PN junctions, and based on the unidirectional conductivity of the PN junction, the base can be easily distinguished. Set the multimeter to the * 1K ohm range, and then assume that one pin of the transistor is the base. Attach the black probe of the multimeter and connect the red probe to the other two pins separately. If the resistance values measured twice are small (forward resistance), and the red probe is connected to the pin assumed to be the base, and the black probe is connected to the other two pins respectively, with high resistance values (reverse resistance), then the assumption is correct, and that pin is the base. The damage to a transistor is mainly due to open or short circuits, and this method can easily determine whether the transistor is damaged.
