How to detect whether the electronic components of the circuit board are good or bad?

The probability of damage to circuit board components is: electrolytic capacitors, power modules, high-power transistor, zener diodes, resistors less than 100Ω, resistors greater than 100kW, relays, and small ceramic capacitors. Electronic components are divided into two categories, one is components and the other is devices. A multimeter is generally used to detect whether it is good or bad, and the component is mainly checked based on its own characteristics. During the maintenance process, a multimeter should be used to detect the quality of electronic components according to the fault condition. If the measurement method is incorrect, it is likely to lead to misjudgment, which will cause difficulties to the maintenance work and even cause unnecessary economic losses.

The measurement method is divided into two methods: component testing and circuit board in-circuit testing. On-road test: Disconnect the power supply of the inverter and measure the components on the circuit board without disassembling the components of 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 measured components on the circuit board and the components in parallel with them on the measurement results should also be considered, so as not to cause misjudgment errors. How to detect whether the electronic components of the circuit board are good or bad?

1.Detection of ordinary diodes: Use an MF47 multimeter to measure, connect the red and black meter pens to both ends of the diode, read the readings, and then adjust the meter pens to measure. Judging from the results of the two measurements, the forward resistance value of a low－power germanium diode is usually 300-500Ω, and the silicon diode with its voltage or amperage values is about 1kW or greater. The inverting resistance of the germanium tube is tens of kiloohms, and the reverse resistance of the silicon tube is above 500kW (the value of the high-power diode is much smaller). A good diode has a lower forward resistance and a larger reverse resistance. The greater the difference between the forward and reverse resistance, the better. If the measured positive and reverse resistors are small and close to zero, it means that the diode has been shorted inside; if the positive and reverse resistors are large or tend to infinity, it means that the tube has been disconnected inside. In both cases, the diode needs to be scrapped. In-circuit test: Test the forward and reverse resistance of the diode PN junction, it is easier to determine whether the diode is a breakdown short circuit or a circuit breaker.

2.Transistor detection: Dial the digital multimeter to the diode gear, and use the meter pen to measure the PN junction. If the forward guide is turned on, the displayed number is the forward voltage drop of the PN junction. First determine the collector and emitter; use the meter pen to measure the forward voltage drop of the two PN junctions. The large voltage drop is the emitter e, and the small voltage drop is the collector C. When testing the two junctions, the red meter pen is connected to the common pole, the transistor under test is NPN type, and the red meter pen is connected to the base b; if the black meter pen is connected to the common pole, the transistor under test is PNP type, and this is the base B. After the transistor is damaged, the PN junction has two conditions: breakdown, short circuit and open circuit. In the road test, the transistor is actually tested by testing the positive and reverse resistance of the PN junction to determine whether the transistor is damaged. The branch resistance is greater than the forward resistance of the PN junction. There should be a clear difference between the forward and reverse resistance measured under normal conditions, otherwise the PN junction will be damaged.When the branch resistance is less than the forward resistance of the PN junction, the branch should be disconnected, otherwise it is impossible to judge the quality of the transistor.

3.The detection of the three-phase rectifier bridge module takes the SEMIKRON (Siemens) rectifier bridge module as an example. Dial the digital multimeter to the diode test file, the black meter pen is connected to COM, and the red meter pen is connected to VΩ. Use the red and black meter pens to test the positive and negative diode characteristics between the 3, 4, and 5 phases and the 2 and 1 poles one after another to check and determine whether the rectifier bridge is intact.The greater the difference in the measured positive and negative characteristics, the better; if the positive and negative direction is zero, it means that the detected phase has been broken through and shorted; if the positive and negative directions are both infinite, it means that the detected phase has been disconnected. As long as the rectifier bridge module is damaged in one phase, it should be replaced.

4.Inverter IGBT module detection: Dial the digital multimeter to the diode test file to test the IGBT module C1.E1, C2. The positive and negative diode characteristics between E2 and the gate G and E1 and E2 are used to determine whether the IGBT module is intact.

5.Detection of electrolytic capacitors: When measuring with an MF47 multimeter, the appropriate range of the multimeter should be selected for electrolytic capacitors of different capacities. According to experience, under normal circumstances, electrolytic capacitors below 47μF can be measured in R×1K gears, and electrolytic capacitors greater than 47μF can be measured in R×100 gears. Connect the red meter pen of the multimeter to the negative electrode of the capacitor and the black meter pen to the positive electrode. At the moment of contact, the multimeter pointer deflects to the right by a large margin, and then gradually rotates to the left until it stops at a certain position (return to the infinite position). The resistance value at this time is the forward leakage resistance of the electrolytic capacitor. The larger this value, the smaller the leakage current and the better the capacitor performance. Then, swap the red and black meter pens, and the multimeter pointer will repeat the above swing phenomenon.

However, the measured resistance value at this time is the inverting leakage resistance of the electrolytic capacitor, which is slightly smaller than the forward leakage resistance. That is, the inverting leakage current is larger than the forward leakage current. Actual experience shows that the leakage resistance of electrolytic capacitors should generally be above a few hundred thousand ohms, otherwise it will not work properly. In the test, if there is no charging phenomenon in the forward and reverse phases, that is, the meter hand does not move, it means that the capacitor capacity disappears or the internal short circuit; if the measured resistance is small or zero, it means that the capacitor has a large leakage or has been broken down and damaged, and can no longer be used.

In-circuit testing: In-circuit testing of electrolytic capacitors should only check for serious leakage or breakdown faults. The accuracy of the test of slight leakage or small-capacity electrolytic capacitors is very poor. In road testing, the influence of other components on the test should also be considered, otherwise the value read out will be inaccurate and will affect normal judgment. Electrolytic capacitors can also use a capacitance meter to detect the capacitance value between the two ends to determine whether the electrolytic capacitor is good or bad.

6.Simple test of inductors and transformers

(1) Inductor test: Use the MF47 multimeter resistance file to test the size of the inductor resistance. If the resistance value of the inductor under test is zero, it means that the internal winding of the inductor has a short circuit fault. Note that the multimeter must be zeroed during operation and tested repeatedly several times. If the resistance value of the inductor under test is infinite, it means that a circuit failure has occurred at the junction of the winding or lead pin of the inductor and the winding.

(2) Simple test of transformer: Insulation performance test: Use a multimeter resistance file R×10K to measure the resistance values between the core and the primary winding, the primary winding and the secondary winding, and the core and the secondary winding respectively, which should all be infinite. Otherwise, it means that the insulation performance of the transformer is poor.

7.Simple test of the resistance value of the resistor: When measuring the resistance of the circuit board, the power supply of the circuit board should be cut off, and the influence of other components in the circuit on the resistance value should be considered.If a capacitor is connected to the circuit, the capacitor must also be discharged.The multimeter hand should be pointed at the center of the scale for the reading to be accurate.

Precautions for detecting electronic components of circuit boards:

1. Under normal circumstances, it needs to be removed for testing. The first is the resistance type and the second is the capacitance type, because these two types 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, it can also be detected online. Good or bad.

2. Before the test, it is best to install it back on the device, repeatedly turn on and off the device to try, and press the reset button a few more times.

3. A short circuit was found. Take a board to secant the line (especially suitable for single/double-layer boards), and after secant the line, each part of the function block is energized separately, and gradually eliminated.