10 kinds of learning methods for inventory maintenance and case analysis

There are many ways to repair and repair the inverter, but the direction is not in vain, so it is very important to catch the direction. In order to let everyone know the maintenance knowledge of the inverter faster, Xiaobian provides ten kinds of learning methods for inverter maintenance training:

1. Alarm parameter check method:

All frequency converters give fault indications in different ways and are very important information for the repairer. Under normal circumstances, the inverter will give corresponding error information for voltage, current, temperature, communication and other faults, and most inverters using microprocessor or DSP processor will have special parameters to save more than 3 alarm records. .

[Example 1] A certain inverter has a fault and cannot be operated. The LED displays “UV” (short for under voltage). In the manual, the alarm is DC bus undervoltage. Because the control loop power of this type of inverter is not taken from the DC bus, but the control power is separately rectified from the AC input through the transformer. So judge that the alarm should be true. Therefore, check from the power supply, the input power supply voltage is correct, and the filter capacitor voltage is 0 volts. Since the short-circuit contactor of the charging resistor does not operate, it is independent of the rectifier bridge. The fault range is reduced to the charging resistor. After the power is turned off, the multimeter is used to detect that the charging resistor is broken. Replace the resistor and fix it immediately.

〖Example 2〗 After a three-inch IF 11Kw inverter has been used for more than three years, “AL5” (abbreviation of alarm 5) is displayed occasionally when power is on. The manual says that the CPU is disturbed. After many observations, it was found that the charging resistor shorted the contactor. Suspected to be the interference caused by the contactor, plus the resistance-capacitance filter on the control pin, the failure no longer occurs.

〖Example 3〗 A Fuji E9 series 3.7 kW inverter, OC3 (constant over-current) alarm shutdown occurred in the field operation, OC1 (acceleration over-current) alarm shutdown occurred after power-off. I first remove the U, V, W to the motor wire, use a multimeter to measure the infinite resistance between U, V, W, no-load operation, the inverter has no alarm, the output voltage is normal. It can be preliminarily determined that the inverter has no problem. It turns out that there is a joint in the middle of the motor cable, which is covered with a wood plate in the dividing slot of the pit. The insulating tape is aging, and the factory cleans the water, causing an output short circuit.

[Example 4] Sanken SVF303, display "5", "5" in the manual indicates DC overvoltage. The voltage value is sampled by the DC bus (DC at about 530V) and then separated by the optocoupler. When the voltage exceeds a certain threshold, the optocoupler acts to give the processor a high level. Overvoltage alarm, we can look at whether the resistance changes, whether the optocoupler has a short circuit.

From the above examples, it is not difficult to see how important the alarm prompt of the inverter is to deal with the problem, prompting you to correctly handle the problem.

2. Analogy check method:

This method can be an analogy of its own circuit, or it can be an analogy between a fault board and a known good board. This can help the repairer quickly narrow the scope of the inspection.

〖Example 1〗 The three-way MF15 kW inverter is damaged and sent back for repair. The user cannot tell the specific situation. First, use a multimeter to measure the input terminals R, S, and T. Except for a certain resistance between R and T, the resistance between the other terminals is infinite. The input terminals R, S, and T are respectively between the positive and negative terminals of the rectifier bridge. Diode characteristics. Why is R and T different from the other two groups? The original R, T break has a control power transformer inside, so there is a certain resistance. The above can be seen that the input part is no problem. Also use a multimeter to check the resistance between U, V, W, three-phase balance. Next, it is found that the output of the diodes of the positive and negative DCs is not connected to the positive and negative poles. It is suspected that there is a problem with the U-phase IGBT. If the IGBT is broken, it is considered that the IGBT is broken. The characteristics of the three sets of upper arm control circuits in the drive circuit are the same, and the characteristics of the three sets of control circuits of the lower arm are the same. The comparison method is used to check that Q1 is damaged. After the replacement, the trigger pin resistance values ​​are the same in each group, and the PWM waveform is confirmed to be correct after power-on. Reassemble, power up test repair.

〖Example 2〗 There is a frequency converter, the phenomenon is that the panel display is normal, the digital setting frequency and operation are normal, but the terminal control fails. Use a multimeter to check that the terminal has no voltage of 10V. Starting from the switching power supply, each group of power supplies is normal, it seems that the problem is on the connecting wires. However, it is really time to find 10V in 32 flat cables without drawings. It just happens to have a good 22KW, so first record the voltage of each foot of the 22KW connecting flat cable, and then compare the 37KW. The voltage of each foot to the ground quickly found a difference. The original socket pin is soldered, and the inverter uses the oxidation effect for a period of time to make it completely non-conductive, and re-weld and repair.

〖Example 3〗 There is a carding machine in the wool spinning factory, using Siemens 440 inverter, two 5.5KW one 7.5KW to achieve synchronous operation. One of the 5.5KW runs often has F0011 or A0511 downtime after two years of operation. These two alarms all indicate that the motor is overloaded. The motor belt is disconnected from the motor belt and the motor is driven by the hand. There is no abnormal heavy phenomenon. The two 5.5KW dragged motors are interchanged. It is found that the original inverter alarm is OK. There is a problem with the drive. The analogy method can be used not only to check the internal loop of the machine, but also to judge the field problem.

3. Backup board replacement inspection method:

It is very effective to use a spare board or a board of the same type to confirm the fault and narrow the inspection range. If there is a problem with the control panel, there is often no other way to replace it, because most users will hardly get the schematic and layout, making it difficult to make chip-level maintenance. Circuit boards other than control boards such as power boards and driver boards can be repaired. Other chapters will be further introduced. This section mainly introduces the replacement of the control boards.

4. Isolation inspection method:

Some faults are often difficult to judge in that area, and isolation can be used to simplify complex problems and find out the cause of the fault faster.

〖Example 1〗 Repair an Intel inverter, the phenomenon is no display after power-on, accompanied by a 嘀--嘀 sound. Based on experience, it can be concluded that the switching power supply is overloaded, and the feedback protection acts to turn off the switching power supply output, and the humming sound is generated when the vibration is turned off again. First remove the control panel, power-on discovery is still the same, then disconnect the diodes of each group of power supply one by one, and finally found that the fan used 15V has a problem. However, the fan does not have a running signal. It should not be a problem with the fan itself. It seems to be a problem with the front end of the fan. Finally, it was found that the 15V filter capacitor characteristics are wrong, and the filter capacitor measurement is removed, which is really aging. Replace it with a new one.

5. Visual inspection method:

It is to use the sensory organs of the human hand, eyes, ears and nose to find the cause of the malfunction. This method is commonly used and used first. The maintenance principle of “before and outside again” requires maintenance personnel to first use the method of looking, smelling, asking, and touching when encountering faults, and checking them one by one from the outside to the inside. Some faults can use this intuitive method to quickly find the cause, otherwise it will waste a lot of time, even impossible to start. Whether the connection of the line component can be loosened by the visual, whether the wire break contactor is ablated by electric shock, whether the pressure is normal, whether the heating element is overheated, whether the electrolytic capacitor is expanded and deformed, and whether the pressure component has a significant breakdown point. After powering up, I smelled if there was a smell of burntness. It is very important to ask, ask the user the process of the failure, help to analyze the cause of the problem, and facilitate direct hits. Sometimes asking peers is also a shortcut.

〖Example 2〗 A Sancha IP 55KW inverter is damaged during the warranty period, and there is no display after power-on. Open the lid of the machine, carefully observe the various parts, and find that the charging resistor burned out, the contactor coil was blown and the shell was burnt. After questioning, the original user power supply voltage is low, the inverter often has a booster for the inverter because of undervoltage shutdown. However, the user did not notice that the voltage would return to normal at night, and as a result, the contactor was first burned and the charging resistor was burned out. It is spared because the rectifier bridge and electrolytic capacitor have relatively high withstand voltage. Replace damaged device repair.

6. Lifting temperature check method:

This method is very effective for some special faults. Artificially warming or cooling some components with poor temperature characteristics, creating "disorders" or eliminating "diseases to find the cause of the malfunction"

〖Example 3〗 There is a Delixi inverter fault. The user reports that the inverter often initializes and stops the parameters, and the fault is reappeared 20 minutes to 30 minutes after the parameters are reset. First of all, I think the fault should be related to temperature, because the temperature of the inverter will rise after running this time. I used a hot air soldering station to heat the thermistor. When it was heated to the temperature at which the fan was turned on, I observed that the LED of the control panel suddenly turned off and then turned on. Then I flashed and then took the hot air for 30 seconds. The LED is no longer flashing, but a normal display. All the fan plugs were removed by the isolation method, and the heating experiment was performed again, and the fault was eliminated. Check that the fans are all shorted. It seems that after the temperature has arrived, the control panel gives the fan operation signal. As a result, the short-circuited fan causes the switching power supply to overload and close the output. The control board quickly loses power and the parameter is stored incorrectly, causing the parameter to be reset. Replace the fan and the problem is solved.

7. Destruction inspection method:

It is to take some measures to cancel internal protection measures and simulate fault conditions to destroy the problematic device. Make the faulty device or area stand out. First of all, declare that this method must have a very good grasp to control the development of the situation, that is, the maintenance personnel should understand the state of the most serious damage, whether it can accept the most serious damage, and have control means to avoid more serious damage.

〖Example 1〗 In the repair of the inverter, a frequency converter with a switching power failure is encountered. His protection circuit operates, and it can be concluded that there is a short-circuit branch at the output of the transformer, but the fault cannot be measured statically. We use the destruction method to find static, trouble-free devices. First, disconnect the feedback signal of the protection circuit, so that it loses the protection function, and then turn on the DC power supply. It is required to use the voltage regulator to gradually increase the DC voltage from 0v and observe the related devices. It was found that there was smoke, and the power was turned off immediately, and the short-circuit DC filter capacitor was quickly discharged by the resistor. The smoke is the rectifier diode of the fan power supply. The original fan has been short-circuited, and the control switch signal of the fan is always on (the device short-circuit causes the high-level open state). As long as the switching power supply outputs normal voltage, the fan is short-circuited. Fan power supply, resulting in switching power supply protection. In the static measurement, the short circuit state of the fan is not detected.

8. Tap check method:

The inverter is composed of connectors for various circuit boards and modules. Each circuit board has many solder joints, and any virtual soldering and poor contact will cause failure. Use an insulated rubber rod to strike a suspected defective part. If the inverter's fault disappears or reappears, the problem is likely to be there.

〖Example 1〗 The inverter of a factory has been running normally for more than 3 years. It suddenly stops without any warning, and there is no fault information displayed. It will stop when it starts. After careful observation, no abnormalities were found, and no static measurements were found. After power-on, tap the housing of the inverter and find that the running signal will change with the tap. After inspection, it was found that the external terminal FR terminal screw was loose, and the U-terminal was not crimped at the running signal end, and it was directly connected to the terminal. The wiring was pressed to the wire of the wire, causing the screw to loosen the vibration and control the wire and terminal. Virtual connection. Crimp the U-shaped terminal and re-tighten the screw to troubleshoot.

9. Brushing inspection method:

Many special faults, sometimes absent, are looming and can't be judged and processed. At this time, you can clean the circuit board with water or alcohol, and use a soft brush to brush the dust and rust on the circuit board, especially pay attention to the place where the solder joint is dense. The via hole and the circuit close to the 0 volt copper layer should also be cleaned. Clean and then blow dry with hot air. It often achieves unexpected results. At least it helps in the application of the observation method.

〖Example 1〗 A certain inverter fault is no display. After preliminary detection, the rectification part and the inverter part are intact, so the power check. The DC bus voltage is normal, but the voltage of the switching power supply control chip 3844 is only 2v. The resistance of the voltage divider resistor is much smaller on-line detection, and offline detection is normal. After the treatment with the scrubbing method, the problem is solved. It turns out that the positive pin pad of a capacitor is very close to the 0v layer, and the residual flux makes it semi-conductive.

[Example 2] When the inverter is sent, there are several different alarm records. Various false alarms also appeared during the power-on test. After carefully cleaning the control board and the drive board to connect the flat cable socket solder joints, the problem is solved.

10. Principle analysis check method:

Principle analysis is the most fundamental method for troubleshooting. When other inspection methods are difficult to work, you can start from the basic principle of the circuit, check step by step, and finally find out the cause of the failure. Using this method, you must have a clear understanding of the principle of the circuit, master the logic level and characteristic parameters (such as voltage value, waveform) at various points at each moment, and then use a multimeter, oscilloscope to measure, and compare with the normal situation, analyze and judge the fault. The reason is to narrow the fault range until a fault is found.

[Example 1] One inverter sent for repair loses the short circuit of the charging resistor short circuit relay, fan operation, and inverter status relay. After a comparative test, the problem was confirmed to be on the control panel. After analysis, the problem may be on the latch because these signals are controlled by this chip. The result of the replacement is fixed.

In general, the faulty inverter is checked from the outside to the inside, from the table to the inside, from static to dynamic, with the main loop to the control loop. The following three checks are generally mandatory.

Use a multimeter to check the diode characteristics and three-phase balance characteristics of the DC positive and negative terminals of the output terminals. This step can preliminarily determine whether the inverter module is good or bad, and thus decide whether it can be no-load output. If there is a phase-to-phase short circuit or an unbalanced state, the output cannot be idling.

Open the cover and observe if there is no problem in the above two steps, you can open the case, remove the dust, carefully observe whether there is damage inside the inverter, whether there is a blackened component, whether the capacitor leaks, etc. The above are ten kinds of learning methods for inverter maintenance. Learning these inverters through these methods will help you get started, further master the richer knowledge, and lay the foundation for mastering the knowledge of inverter maintenance.