Multimeter to detect the quality of electronic components

In the maintenance process, according to the quality of the failure situation, if the measurement method is not correct, it is likely to cause misjudgment, which will cause difficulties in the maintenance work and even cause unnecessary economic losses. The measurement method is divided into two methods: component test and circuit board in-circuit test. In-circuit test: disconnect the inverter power supply, and measure the components on the circuit board without disassembling the circuit board components. For component breakdown, short circuit, and open circuit faults, this detection method can quickly and easily find the damaged components, but the influence of the components tested on the circuit board and the components connected in parallel on the measurement results should also be considered , So as not to cause misjudgment errors. The following describes how to judge the quality of components:

One, the detection of ordinary diodes

Use the MF47 type multimeter to measure, connect the red and black test leads to the two ends of the diode respectively, read the readings, and then exchange the test leads for measurement. Judging from the two measurement results, the forward resistance of low-power germanium diodes is usually 300-500Ω, and silicon diodes are about 1kΩ or more. The reverse resistance of the germanium tube is tens of kiloohms, and the reverse resistance of the silicon tube is above 500kΩ (the value of the high-power diode is much smaller). A good diode has a lower forward resistance and a larger reverse resistance. The larger the difference between the forward and reverse resistance, the better. If the measured forward and reverse resistances are very small and close to zero, it means that the diode has a short circuit; if the forward and reverse resistances are very large or tend to infinity, it means that the inside of the tube is open. In both cases, the diode needs to be scrapped.

In-circuit test: Test the forward and reverse resistance of the PN junction of the diode, it is easier to judge whether the diode is a short-circuit or an open circuit.

Diode and triode detection

Set the digital multimeter to the diode position and measure the PN junction with a test pen. If the forward conduction is conducted, the displayed number is the forward voltage drop of the PN junction.

First determine the collector and emitter; measure the forward voltage drop of the two PN junctions with a meter pen, the emitter e is the larger voltage drop, and the collector c is the smaller voltage drop. When testing two junctions, the red test lead is connected to the common pole, then the tested transistor is of NPN type, and the red test lead is connected to the base electrode b; if the black test lead is connected to the common pole, the tested transistor is of PNP type. And this is extremely base b. After the triode is damaged, the PN junction has two kinds of situations: short-circuit and open-circuit.

In-circuit test: In-circuit test of the transistor, in fact, is to judge whether the transistor is damaged by testing the forward and reverse resistance of the PN junction. The branch resistance is greater than the forward resistance of the PN junction. Normally, the measured forward and reverse resistance should be significantly different, 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 the quality of the triode cannot be judged.

Three-phase and three-phase bridge rectifier module detection

Take SEMIKRON (Siemens) rectifier bridge module as an example, as shown in the attached picture. Set the digital multimeter to the diode test position, connect the black test lead to COM, and connect the red test lead to VΩ. Use the red and black test leads to test the forward and reverse diode characteristics between phases 3, 4, and 5 and between 2 and 1 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 are zero, it means that the detected phase has been broken down and short-circuited; if the forward and reverse are both infinite, it means that the detected phase has been disconnected. As long as one phase of the rectifier bridge module is damaged, it should be replaced. : Transmission and Distribution Equipment Network

Fourth, the experience of MOS tube quality

1: Connect the black test lead to the D pole and the red test lead to the S pole. Generally, there is a resistance value of 500-600

2: On the premise that the black test lead does not move, use the red test lead to tap the G pole, and then use the red pen to measure the S pole, there will be conduction

3: Connect the red test lead to the D pole, the black test lead to the G pole and then to the S pole. The measured resistance is the same as that measured in 1, indicating that the MOS tube is working normally~~

The following methods are summarized during the repair process. On the board, without the CPU, directly hit the resistance of S and G. If it is less than 30 ohms, it is basically broken. You can compare it to the above

The method of measuring MOS tube with digital multimeter: (using the 2-pole tube file) method to remove the broken tube for measurement

5. Inverter IGBT module detection

Set the digital multimeter to the diode test file to test the forward and reverse diode characteristics between the IGBT modules C1.E1, C2.E2 and between the gate G and E1, E2 to judge whether the IGBT module is intact.

Take Germany eupec25A/1200V six-phase IGBT module as an example, (refer to the attached picture). Remove the U, V, and W phase wires on the load side, use the diode test file, connect the red test lead to P (collector C1), and then test U, V, W (emitter E1) with the black test lead. The multimeter displays the value as; Conversely, connect the black test lead to P and the red test lead to measure U, V, W, and the multimeter will display a value of about 400. Then connect the red test lead to N (emitter E2), the black test lead to measure U, V, W, the multimeter displays about 400; the black test lead to N, the red test lead to measure U, V, W (collector C2), the multimeter displays the value for. The forward and reverse characteristics of each phase should be the same. If there is a difference, it means that the performance of the IGBT module has deteriorated and should be replaced. When the IGBT module is damaged, only the breakdown short-circuit occurs.

The red and black test leads respectively measure the forward and reverse characteristics between the gate G and the emitter E. The values measured by the multimeter are both times. At this time, it can be judged that the gate of the IGBT module is normal. If there is a numerical display, the performance of the gate is degraded, and the module should be replaced. When the positive and negative test results are zero, it means that the detected one-phase gate has been broken down and short-circuited. When the gate is damaged, the voltage regulator tube of the circuit board to protect the gate will also be broken down and damaged.

Six, the 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, in general, electrolytic capacitors below 47μF can be measured at the R×1K gear, and electrolytic capacitors larger than 47μF can be measured at the R×100 gear.

Connect the red test lead of the multimeter to the negative electrode of the capacitor and the black test lead to the positive electrode. At the moment of contact, the pointer of the multimeter will deflect to the right by a large amount, and then gradually rotate to the left until it stops at a certain position (returns to the 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 performance of the capacitor. Then, swap the red and black test leads, and the multimeter pointer will repeat the above-mentioned swinging phenomenon. But at this time, the measured resistance value 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 more than several hundred kiloohms, otherwise it will not work properly.

In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the hands of the watch do not move, it means that the capacitance of the capacitor has disappeared or the internal short circuit; if the measured resistance value is very small or zero, it means that the capacitor has a large leakage or has been broken down. Can no longer be used.

On-the-road test: On-road testing of electrolytic capacitors should only check for serious leakage or breakdown faults. The accuracy of the test for minor leakage or small-capacity electrolytic capacitors is very poor. The in-circuit test should also consider the impact of other components on the test, otherwise the readout value will be inaccurate, which will affect the normal judgment. Electrolytic capacitors can also use a capacitance meter to detect the capacitance value between the two ends to judge the quality of the electrolytic capacitor.

Seven, inductor and transformer simple test

  1. Inductor testing

Use the MF47 type multimeter to test the resistance of the inductor. If the resistance value of the inductor under test is zero, it indicates that the internal winding of the inductor has a short-circuit fault. Note that the multimeter must be zeroed during operation, and the test must be repeated several times. If the resistance of the measured inductor is infinite, it indicates that an open circuit fault has occurred at the winding or lead-out pin of the inductor and the winding contact.

: Transmission and Distribution Equipment Network

  2. Simple test of transformer

Insulation performance test: Use a multimeter to measure the resistance between the core and the winding, the winding and the secondary winding, and the core and the secondary winding with a multimeter resistance file R×10K. The resistance values should all be infinite. Otherwise, the insulation performance of the transformer is poor.

Measure winding continuity: use a multimeter to measure the resistance between each winding of the transformer and the secondary with a multimeter R×1. Generally, the resistance of the winding should be tens of ohms to hundreds of ohms. The smaller the transformer power, the greater the resistance value; Winding resistance is generally a few ohms to hundreds of ohms. If the resistance value of a certain group is infinite, then the group has an open circuit fault

Note: This measurement method is only a rough estimate. Some transformers with slight short-circuit insulation between windings cannot be detected accurately.

8. Simple test of resistance value of resistor

When measuring resistance on the road, cut off the power supply 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 needle of the multimeter should point to the center of the scale for accurate readings.

Nine, SMD components

1. Types of SMD components

Inverter electronic circuit boards now mostly use SMD components, also known as surface mount components, which are micro-miniature electronic components suitable for surface mounting without leads or with very short leads. There are many varieties and specifications of SMD components, which can be divided into rectangular, cylindrical and special-shaped structures according to their shapes. According to the type, it can be divided into chip resistors, chip capacitors, chip inductors, chip semiconductor devices (can be divided into chip diodes and chip transistors), and chip integrated circuits. : Transmission and Distribution Equipment Network

2. Demolition and soldering of SMD components

Use 35W internal heating electric soldering iron with long-life oxidation-resistant tip. Wipe up the residue on the tip of the soldering iron, leaving only a thin layer of solder. It is easier to disassemble and weld the SMD components of the two ends of the device. SMD integrated circuits have thin and many pins, small pin spacing, and compact arrangement of surrounding components, making it difficult to disassemble and assemble. Their disassembly and soldering are difficult without special tools. This article focuses on the disassembly and soldering operations of SMD integrated circuits.

3. Disassembly method

If it has been judged that the integrated circuit block is damaged, use a paper cutter to cut the pins all at the root and remove the integrated circuit block. Note that the cutter head should not cut to the circuit board when cutting. Then, clamp the broken feet with tweezers, use a pointed soldering iron to melt the solder on the broken feet, and remove the broken feet one by one.

4. Welding method

Before soldering, use alcohol to clean the excess solder and dirt on the copper lining of the circuit board from which the integrated circuit block is removed. Coat the pins of the integrated circuit block with alcohol rosin, and coat the pins with a thin layer of tin. . Then, check the position of the integrated circuit pins, place the integrated circuit block on the circuit board to be soldered, lightly press the integrated circuit block, and use an electric soldering iron to first solder the pins on the four corners of the integrated circuit block to fix the integrated circuit block OK, then solder the other pins one by one. In order to ensure the welding quality, when welding, use a thinner solder wire, such as 0.6mm solder wire, and the welding effect will be better.