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Ten methods of inverter maintenance (part 2)

Apr 08, 2021

Ten methods of inverter maintenance (part 2)


  6, temperature rise and fall inspection method


  This method is very effective for some special faults. Artificially heat or cool some components with poor temperature characteristics to produce "sickness" or eliminate "sickness" to find the cause of the failure


  〖Example〗A Delixi inverter failed. Users report that the inverter often initializes and shuts down through parameter initialization. Generally, the fault recurs within 20 to 30 minutes after resetting the parameters. First of all, I think the fault should be related to temperature, because the temperature of the inverter will rise after running to this time. I used a hot-air soldering station to heat the thermistor. When it was heated to the temperature at which the fan started, I observed that the LED on the control panel was suddenly powered off and then turned on again. Then it flashed lightly and dimly. After removing the hot air for 30 seconds, the control panel The LED is no longer flashing, but a normal display. Use the isolation method to unplug all the fan plugs, and re-heat the experiment to eliminate the fault. All the fans are found to be short-circuited. It seems that after the temperature is reached, the control board gives a fan operation signal. As a result, the short-circuited fan causes the switching power supply to be overloaded and shuts down the output. The control board loses power quickly and the parameter storage is wrong, causing the parameter to be reset. Replace the fan and the problem is solved.


   7. Destruction inspection method


   is to take some means to cancel the internal protection measures and simulate the fault condition to destroy the problematic device. Make the faulty device or area stand out. First of all, it is stated that this method must be very sure to control the development of the situation, that is, the mentality of the repairer must understand the state of the most serious damage, whether it can accept the most serious further damage, and have control methods to avoid more serious damage. damage.


  〖Example〗 In repairing the inverter, when a switching power supply fails, its protection circuit is activated, and it can be concluded that there is a short circuit at the output of the transformer, but the fault point cannot be measured in a static state. We use the destruction method to find static and trouble-free devices. First, disconnect the feedback signal of the protection circuit to make it lose the protection function, and then switch on the DC power supply, requiring a voltage regulator to slowly increase the DC voltage from 0v, and observe the related devices. If there is smoke coming out, turn off the power immediately, and use a resistor to short-circuit the DC filter capacitor to quickly discharge it. The smoke is the rectifier diode of the fan power supply. The fan has been short-circuit damaged, and the control switch signal of the fan is always on (the device is short-circuited and the high-level open state). As long as the switching power supply outputs a normal voltage, the fan will be short-circuited. Fan power supply, resulting in switching power supply protection. In the static measurement, the short-circuit state of the fan cannot be measured.


   8. Percussion inspection method


  Inverter is composed of various circuit boards and connectors for modules. Each circuit board has many solder joints. Any false soldering or poor contact will cause malfunctions. Knock the suspected defective part with an insulated rubber rod. If the fault of the inverter disappears or reappears, it is likely that the problem lies there.


   [Example] The inverter of a certain factory has been in normal operation for more than 3 years, and suddenly stopped without any signs, and there is no fault information displayed. After starting, it will turn and stop. Observation carefully, no abnormalities were found, and no problems were found in the static measurement. After power-on, knock on the housing of the inverter and find that the running signal will change with the knock. After inspection, it was found that the FR terminal screw of the external terminal was loose, and the operating signal line end was not crimped with the U-shaped terminal, and it was directly connected to the terminal. The wiring was pressed against the wire skin, causing the screw to loosen due to vibration, and the control line wire and terminal Virtual connection. Crimp the U-shaped terminal and re-tighten the screw to eliminate the fault.


   9. Brushing inspection method


   There are many special faults, sometimes and not, and looming, making it impossible to judge and deal with. At this time, you can clean the circuit board with water or alcohol. At the same time, use a soft brush to remove the dust and rust on the circuit board. Pay special attention to the places with dense solder joints, and clean the vias and the circuits close to the 0V copper layer. Clean, then dry with hot air. Will often achieve unexpected results. At least it helps the application of the observation method.


  〖Example 1〗There is no display for a certain inverter fault. After preliminary inspection, the rectifier part and the inverter part are intact, so power on for inspection. The DC bus voltage is normal, but the starting voltage of the switching power supply control chip 3844 is only 2v. The resistance value of the voltage divider is much smaller in the online detection, and the offline detection is normal. After the scrubbing method is used, 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 in a semi-conductive state.


  〖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 solder joints of the flat cable sockets connected between the control board and the drive board, the problem is solved.


  10. Principle analysis and inspection method


  Principle analysis is the most fundamental method of troubleshooting. When other inspection methods are difficult to work, you can proceed from the basic principles of the circuit to check step by step, and finally find out the cause of the failure. To use 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 each point at each time, and then measure it with a multimeter and an oscilloscope, and compare it with the normal situation to analyze and judge the fault Reason, narrow the scope of the fault until the fault is found.


   [Example] An inverter sent for repair loses the charging resistance short-circuit relay, fan operation, and inverter status relay signals at the same time. After comparative tests, it was confirmed that the problem lies in the control board. After analysis, the problem may lie in the latch, because these signals are controlled by this chip. The replacement will be repaired.


   Generally speaking, the inspection of the faulty inverter should be from the outside to the inside, from the surface to the inside, from static to dynamic, from the main loop to the control loop. The following three checks are generally required.


   Use a multimeter to detect the diode characteristics and the three-phase balance characteristics of the output terminals to the DC anode and cathode respectively. This step can preliminarily determine the quality of the inverter module and determine whether it can output without load. If there is a phase-to-phase short circuit or an unbalanced state, no-load output is allowed.


  Open the cover and observe. If no problems are found in the above two steps, you can open the case, remove the dust, and carefully observe whether there is any damage inside the inverter, whether there are scorched parts, whether the capacitor is leaking, etc.


   The above are ten learning methods for inverter maintenance. Learning inverter maintenance through these methods will help you get a better entry, and further master more abundant knowledge, and make a good foundation for proficiency in learning inverter maintenance knowledge.