How to detect the quality of circuit board electronic components?

Date：2021-10-25 16:14:00Views：2766

The damage probability of circuit board components is as follows: electrolytic capacitor, power module, high-power transistor, zener diode, resistance less than 100 Ω, resistance greater than 100k Ω, relay and porcelain chip small capacitance. Electronic components are divided into two categories: components and devices. The quality of the test is generally measured with a multimeter, and the components are mainly checked according to their own characteristics. In the maintenance process, use a multimeter to detect the quality of electronic components according to the fault conditions. If the measurement method is incorrect, it is likely to lead to misjudgment, which will cause difficulties to the maintenance work and even unnecessary economic losses.

The measurement methods are divided into component test and circuit board on-the-road test. In circuit test: disconnect the power supply of the frequency converter and measure the components on the circuit board without removing the components on the circuit board. For component breakdown, short circuit and open circuit faults, this detection method can easily and quickly find out the damaged components, but the impact of the components measured on the circuit board and the components connected in parallel on the measurement results should also be considered to avoid misjudgment. How to detect the quality of circuit board electronic components?

1. Detection of ordinary diode: measure with mf47 multimeter, connect the red and black probes at both ends of the diode respectively, read the readings, and then adjust the probes for measurement. According to the two measurement results, the forward resistance of low-power germanium diode is usually 300-500 Ω, and that of silicon diode is about 1K Ω or more. The reverse resistance of germanium tube is tens of kiloohms, and the reverse resistance of silicon tube is more than 500K Ω (the value of high-power diode is much smaller). Good diodes have low forward resistance and large reverse resistance. The greater the difference between forward and reverse resistance, the better. If the measured forward and reverse resistances are very small and close to zero, it indicates that the diode has been short circuited internally; If the forward and reverse resistance is very large or tends to infinity, it indicates that there is an open circuit inside the pipe. In both cases, the diode needs to be scrapped. In circuit test: test the forward and reverse resistance of diode PN junction, and it is easier to judge whether the diode is broken down, short circuit or open circuit.

2. Triode detection: turn the digital multimeter to the diode position and measure the PN junction with the probe. If the forward is on, the displayed number is the forward voltage drop of the PN junction. First determine the collector and emitter; Use the probe to measure the forward voltage drop of the two PN junctions. The emitter E has a large voltage drop and the collector C has a small voltage drop. When testing two junctions, if the red probe is connected to the common pole, the tested triode is NPN type, and the red probe is connected to the base B; If the black probe is connected to the common pole, the tested triode is PNP type, and this pole is the base B. After the triode is damaged, the PN junction has two situations: breakdown, short circuit and open circuit. In circuit test: in fact, the triode is tested to judge whether the triode is damaged by testing the forward and reverse resistance of the PN junction. The branch resistance is greater than the forward resistance of PN junction. There shall be obvious difference between the forward and reverse resistance measured under normal conditions, otherwise the PN junction is damaged. When the branch resistance is less than the forward resistance of PN junction, the branch should be disconnected, otherwise the quality of triode cannot be judged.

3. The detection of three-phase rectifier bridge module takes Semikron (Siemens) rectifier bridge module as an example. Turn the digital multimeter to the diode test gear, the black probe is connected to com, and the red probe is connected to V Ω. Use the red and black probes to successively measure the forward and reverse diode characteristics between 3, 4 and 5 phases and 2 and 1 poles to check and judge whether the rectifier bridge is intact. The greater the difference between the measured forward and reverse characteristics, the better; If the forward and reverse directions are zero, it indicates that the detected phase has been broken down and short circuited; If both forward and reverse directions are infinite, it indicates that one phase detected has been open circuit. The rectifier bridge module should be replaced as long as one phase is damaged.

4. Inverter IGBT module detection: turn the digital multimeter to diode test gear to test IGBT module C1 E1、C2. The forward and reverse diode characteristics between E2 and between grid g and E1 and E2 can judge whether the IGBT module is intact.

5. Detection of electrolytic capacitors: when measuring with mf47 multimeter, the appropriate range of multimeter shall be selected for electrolytic capacitors with different capacities. According to experience, in general, 47 μ R is available for electrolytic capacitors below F × 1K gear measurement, greater than 47 μ The electrolytic capacitor of F can be used as R × 100 gear measurement. Connect the red lead of the multimeter to the negative pole of the capacitor and the black lead to the positive pole. At the moment of contact, the pointer of the multimeter will deflect to the right by a large margin, and then turn to the left gradually until it stops at a certain position (return to infinity position). The resistance value at this time is the forward leakage resistance of electrolytic capacitor. The larger the value, the smaller the leakage current and the better the performance of the capacitor. Then, adjust the red and black probes, and the multimeter pointer will repeat the above swing phenomenon.

However, the measured resistance is the reverse leakage resistance of electrolytic capacitor, which is slightly less than the forward leakage resistance. That is, the reverse leakage current is greater than the forward leakage current. Practical experience shows that the leakage resistance of electrolytic capacitor should be more than several hundred kiloohms, otherwise it will not work normally.In the test, if there is no charging phenomenon in the forward and reverse phases, that is, the gauge needle does not move, it indicates that the capacity of the capacitor has disappeared or there is an internal short circuit; If the measured resistance value is very small or zero, it indicates that the capacitor has large leakage or has been broken down and damaged and can not be used again.

In circuit test: in circuit test of electrolytic capacitor should only check the fault of serious leakage or breakdown, and the test accuracy of slight leakage or small capacity electrolytic capacitor is very poor. The influence of other components on the test shall also be considered in the on-line test, otherwise the read value will be inaccurate and will affect the normal judgment. The capacitance meter can also be used to detect the capacitance between the two ends of the electrolytic capacitor to judge the quality of the electrolytic capacitor.

6. Simple test of inductor and transformer

(1) Test of inductor: use the resistance gear of mf47 multimeter to test the resistance of inductor. If the resistance value of the tested inductor is zero, it indicates that there is a short circuit fault in the internal winding of the inductor. Note that the multimeter must be zeroed and tested several times. If the resistance of the tested inductor is infinite, it indicates that there is an open circuit fault at the winding or lead out pin and winding contact of the inductor.

(2) Simple test of transformer: insulation performance test: use multimeter resistance gear R × 10K respectively measure the resistance between the iron core and the primary winding, the primary winding and the secondary winding, and the resistance between the iron core and the secondary winding, which shall be infinite. Otherwise, the insulation performance of the transformer is poor.

7. Simple test of resistance value of resistor: cut off the power supply of the circuit board when measuring the resistance, and consider the influence of other components in the circuit on the resistance value. If a capacitor is connected in the circuit, the capacitor must also be discharged. The multimeter needle should point to the center of the scale to read accurately.

Precautions for testing circuit board electronic components:

1. Generally, it needs to be removed for detection. The first is resistance and the second is capacitance, because these two kinds of components are often connected in series and parallel in the circuit. If it is determined that they are not connected in series and parallel, they can also be tested online.

2. Before the test, it is best to reinstall the equipment, turn on and off the machine repeatedly, and press the reset key several times.

3. A short circuit is found. Take a board to cut the line (especially suitable for single / double-layer boards). After cutting, power on each part of the functional blocks respectively and eliminate them step by step.

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