1. Detection of ordinary diodes
Use the MF47 multimeter to measure, connect the red and black watch pens to the two ends of the diode, read the reading, and then adjust the watch pen to measure. According to the results of two measurements, the forward resistance value of the general low-power germanium diode is 300-500Ω, and the silicon diode is about 1kΩ or greater. The inverting resistance of the germanium tube is tens of kiloohms, 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 lower forward resistance and a larger reverse resistance, and the larger the difference between the forward and reverse resistance, the better. If the measured forward and reverse resistance is very small and close to zero, it means that the diode has been short-circuited. If the forward and reverse resistance is large or tends to infinity, it means that the inside of the tube has been opened. In both cases, the diode needs to be deactivated.
On-circuit test: Test the forward and reverse resistance of the diode's PN junction, and it is relatively simple to determine whether the diode is a breakdown short circuit or an open circuit.
2. Transistor detection
Dial the digital multimeter to the diode file, and measure the PN junction with the meter pen, if the guide is positive, the displayed number is the positive voltage drop of the PN junction.
Confirm the collector and emitter first; The forward voltage drop of the two PN junctions is measured with a table pen, the emitter e with the largest voltage drop and the collector c with the small voltage drop. When testing the two knots, the red pen is connected to the common pole, the tested transistor is NPN type, and the red table pen is connected to the base b; If the black pen is connected to a common pole, the transistor under test is of the PNP type, and this electrode is base b. After the transistor is damaged, the PN junction has two situations: breakdown, short circuit and open circuit.
On-road test: The on-road test triode is actually by testing the forward 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, and there should be a significant difference between the forward and reverse resistance measured under normal conditions, otherwise the PN junction will be damaged. When the resistance of the branch is less than the forward resistance of the PN junction, the branch should be disconnected, otherwise the quality of the transistor cannot be distinguished.
3. Three-phase rectifier bridge module detection
Take the SEMIKRON rectifier bridge module as an example, as shown in the attached figure. Dial the digital multimeter to the diode test file, connect the black pen to the COM, connect the red pen to VΩ, and use the red and black pen to measure the characteristics of the forward and reverse diodes between the 3rd, 4th, and 5th phases and the 2nd and 1st poles successively to check whether the rectifier bridge is defective. The greater the difference between the measured forward and reverse characteristics, the better; If the forward and reverse are zero, it indicates that the detected phase has been broken down and short-circuited; If both forward and reverse are infinity, it indicates that the detected phase has been broken. The rectifier bridge module should be replaced if only one phase is damaged.
Fourth, inductors and transformers simple test
1. Inductor test
Use the MF47 multimeter resistance level to test the size of the inductor's resistance. If the resistance of the inductor under test is zero, it indicates that there is a short circuit in the internal windings of the inductor. Note that when operating, be sure to zero the multimeter and repeat the test a few times. If the resistance of the inductor under test is infinite, it indicates that there is a broken circuit in the winding of the inductor or at the contact between the pins and the windings.
2. Simple test of transformer
Insulation performance test: use the multimeter resistance file R×10K to measure the resistance value between the core and the primary winding, the primary winding and the secondary winding, and the core and the secondary winding, which should be infinite. Otherwise, it is clear that the insulation performance of the transformer is poor.
Measure the winding on-off: use the multimeter R×1 gear, separate from the measurement of the resistance value between the primary and secondary windings of the transformer, generally the resistance value of the primary winding should be tens of ohms to hundreds of ohms, the smaller the transformer power, the greater the resistance value; The resistance value of the secondary winding is generally a few ohms to several hundred ohms, if the resistance value of a certain group is infinite, then the group has a broken circuit problem
Note: This measurement method is only a relatively rough estimate, and some transformers with slight short circuits of insulation between winding turns are inaccurate.
5. A simple test of the resistance value of the resistor
When measuring the resistance in the circuit, the power supply of the circuit board should be blocked, and the influence of other components in the circuit on the resistance value should be considered. If there is a capacitor in the circuit, the capacitor must also be discharged. The multimeter hand should point to the center of the scale for accurate readings.
6. SMD components
1. Varieties of SMD components
Most of the inverter electronic circuit boards now use SMD components, also known as surface assembly components, which are a kind of micro electronic components that have no leads or have very short leads and are suitable for surface assembly. There are many standards for the variety 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.
2. Dismantling and soldering of SMD components
A 35W internal heating electric soldering iron is used, and a long-life oxidation-resistant tip soldering iron tip is used. Wipe the residue off the tip of the soldering iron clean, leaving only a thin layer of solder. The SMD components of the two-end device are relatively simple to disassemble and solder. SMD integrated circuits have thin and many pins, small pin spacing, and compact placement of surrounding components, which is not easy to disassemble and assemble. Their disassembly and soldering are difficult without special tools, and the disassembly and soldering operations of SMD integrated circuits are highlighted here.
3. Dismantling method
If the IC block is damaged, use a paper cutter to block the pins and remove the IC block. Pay attention not to cut the cutter head to the circuit board when cutting. Then, clamp the broken foot with tweezers, use a pointed soldering iron to melt the solder on the broken foot, and remove the broken foot one by one.
4. Welding method
Before soldering, clean the remaining solder and dirt on the copper of the circuit board where the integrated circuit block is removed with alcohol, coat the pins of the integrated circuit block with alcohol rosin, and coat the pins with a thin layer of tin. Then, check the orientation of the integrated circuit pins, put the integrated circuit block on the circuit board to be soldered, press the integrated circuit block lightly, use an electric soldering iron to solder the pins on the four corners of the integrated circuit block, fix the integrated circuit block, and then solder the other pins one by one. In order to ensure the quality of welding, it is best to use thinner solder wire, such as 0.6mm solder wire, when welding, the soldering effect is better.
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