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Home > Connector > How to judge the quality of electronic components on the circuit board

How to judge the quality of electronic components on the circuit board

Published time: 2019-07-18

Electronic components are divided into two categories, one is components, and the other is devices. The detection is good and the general use of the multimeter, the component is mainly checked according to its own characteristics.

In the maintenance process, according to the fault situation, the multimeter should be used to detect the quality of the electronic components. If the measurement method is incorrect, it may lead to misjudgment, which will cause difficulties in maintenance work and even cause unnecessary economic losses. The measurement method is divided into two methods: component testing and circuit board testing. In the road test: disconnect the inverter power supply, and measure the components on the circuit board without disassembling the components of the circuit board. For component breakdown, short circuit, open circuit fault, this detection method can find out the damaged components conveniently and quickly, but also should consider the influence of the components measured on the circuit board and the components connected in parallel on the measurement results. In order to avoid misjudgment errors. The following describes the method for judging the quality of electronic components:

1. Detection of common diode

measure with MF47 multimeter, connect the red and black test leads to the two ends of the diode, read the reading, and then measure the test lead. Judging from the two measurements, the low power 锗 diode usually has a forward resistance of 300-500 Ω and a silicon diode of about 1 kΩ or more. The reverse-phase resistance of the manifold is several tens of kilo-ohms, and the reverse resistance of the silicon tube is more than 500kΩ (the value of the high-power diode is much smaller). A good diode has a low forward resistance and a large reverse resistance. The larger the forward and reverse resistance differences, the better. If the measured positive and negative resistances are close to zero, the internal diode is short-circuited; if the positive and negative resistances are large or tend to infinity, the inside of the tube is open. In both cases the diode needs to be scrapped. In the road test: test the diode PN junction forward and reverse resistance, it is easier to determine whether the diode is a short circuit or an open circuit.

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2. Transistor detection

Turn the digital multimeter to the diode file and measure the PN junction with the meter. If it is conducting the conduction, the displayed number is the positive voltage drop of the PN junction. First determine the collector and emitter; use the meter to measure the two. The forward voltage drop of the PN junction, the emitter drop e is large, and the collector c is small. When testing two knots, the red pen is connected to the common pole, then the measured triode is NPN type, and the red test pen is connected to the base b; if the black pen is connected to the common pole, the measured triode is PNP type. And this is extremely base b. After the triode is damaged, the PN junction has a breakdown short circuit and an open circuit. In the road test: the triode in the road test, in fact, by testing the positive and negative resistance of the PN junction, to determine whether the triode is damaged. The branch resistance is greater than the forward resistance of the PN junction. The normal and reverse resistances measured at normal should be significantly different, otherwise the PN junction is damaged. When the branch resistance is less than the forward resistance of the PN junction, the branch should be disconnected, otherwise the triode cannot be judged.

3. Three-phase rectifier bridge module detection Take the SEMIKRON (Siemens) rectifier bridge module as an example. 

Turn the digital multimeter to the diode test file, connect the black meter to the COM, the red meter to the VΩ, and use the red and black pens to measure the forward and reverse diode characteristics between the 3, 4, 5 and 2 poles. Is the rectifier bridge intact? The larger the difference between the measured forward and reverse characteristics is, the better; if the positive and negative directions are zero, it means that the detected one phase has been broken through; if the positive and negative directions are infinite, it means that the detected phase has been broken. The rectifier bridge module should be replaced as long as one phase is damaged.

4. Inverter IGBT module detection

Turn the digital multimeter to the diode test file, test the forward and reverse diode characteristics between the IGBT module C1.E1, C2.E2 and between the gate G and E1, E2 to judge the IGBT module. Is it intact?

5. Detection of electrolytic capacitors

When measuring with an MF47 type multimeter, the appropriate range of the multimeter should be selected for electrolytic capacitors of different capacities. According to experience, in general, electrolytic capacitors below 47μF can be measured in R × 1K, and electrolytic capacitors larger than 47μF can be measured in R × 100. "br" connects the red meter of the multimeter to the negative pole of the capacitor, and the black meter is connected to the positive pole. At the moment of contact, the pointer of the multimeter is deflected to the right by a large amplitude, and then gradually turns to the left until it stops at a certain position (returns to infinity position). The resistance at this time is the forward leakage resistance of the electrolytic capacitor. The larger the value, the smaller the leakage current and the better the capacitor performance. Then, the red and black test leads are reversed, and the multimeter pointer repeats the above swing phenomenon.

However, the resistance measured at this time is the reverse leakage resistance of the electrolytic capacitor, which is slightly smaller than the forward leakage resistance. That is, the reverse leakage current is larger than the forward leakage current. Practical experience shows that the leakage resistance of electrolytic capacitors should generally be several hundred kilo ohms or more, otherwise it will not work properly.

In the test, if there is no charging phenomenon in the forward direction and the reverse phase, that is, the needle does not move, it means that the capacitor capacity disappears or the internal short circuit; if the measured resistance value is small or zero, the capacitor leakage is large or the breakdown is damaged. Can no longer be used. "br" in the road test: in the road test electrolytic capacitors should only check for serious leakage or breakdown failure, the accuracy of light leakage or small-capacity electrolytic capacitor test is very poor. The road test should also consider the influence of other components on the test, otherwise the value read will be inaccurate and will affect the normal judgment. The electrolytic capacitor can also use a capacitance meter to detect the capacitance between the two ends to judge whether the electrolytic capacitor is good or bad.

6. Inductor and transformer easy test

(1) Inductor test

Test the resistance value of the inductor with the MF47 type multimeter resistance file. If the resistance of the tested inductor is zero, it indicates that the internal winding of the inductor has a short circuit fault. Be sure to zero the multimeter and repeat the test several times. If the measured resistance of the inductor is infinite, it indicates that an open circuit fault has occurred at the winding of the inductor or the pin and the winding contact.

(2) Simple test of transformer

Insulation performance test: The resistance value between the core and the primary winding, the primary winding and the secondary winding, and the core and the secondary winding are respectively measured by the multimeter resistance file R×10K, and should be infinite. Otherwise, the transformer insulation performance is poor.

7. Resistor resistance test

When cutting the circuit board power, cut off the power of the circuit board, and consider the influence of other components in the circuit on the resistance value. If a capacitor is connected to the circuit, the capacitor must also be discharged. The multimeter's hands should refer to the center of the scale and the readings are accurate.

 

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