Siemens inverter maintenance example 1: Siemens MMV 6SE3221 4.0kW inverter repair Static measurement inverter module is normal, rectifier module damage.
Failure Analysis and Judgment: Rectification module damage is usually caused by DC load overload, short circuit and element aging.
Measure the reverse resistance value between PN (multimeter positive table pen N, negative table pen P), it can reflect whether there is overload and short circuit of DC load. Measured PN between the resistance value of 15052, the normal value should be tens of kiloohms, indicating that the DC load overload;
Inverter module is normal, can be excluded; check the filter capacitor, voltage balance resistor is normal; test brake switch device damage short circuit,
Remove the brake switch device and check the normal PN resistance. (Siemens inverter repair example)
Replace the brake switch device and the inverter will resume operation.
This fault may be caused by the deceleration time setting of the inverter being too short, causing a large braking current during braking to damage the brake switching device VT. When the brake switch device is damaged and short-circuited, the braking resistor is placed directly between the PNs, generating a large current (approximately 1/2 of the rated current). (Siemens inverter repair example)
During the operation of the inverter, the load current of the rectifier module is the sum of the normal load current and the current flowing through the braking resistor. The rectifier module is damaged due to long-term operation under overload conditions. If the production process allows, increasing the deceleration time can prevent this failure from happening again. (Siemens inverter repair example)
Siemens inverter repair example 2: Siemens MM420 inverter maintenance 37kW
The static detection of the inverter module is normal and the rectifier module is damaged.
Detect reverse resistance between PN is less than normal. Open the inverter and find that the large capacitor combination filter circuit on the printed circuit board has the liquid traces from the large capacitor, and further check that there are two filter large capacitors that have damaged the fluid and have serious leakage.
Replace the capacitor, clean the filter and capacitor combination printed circuit board, and then measure the normal reverse resistance between PN, and the inverter will resume normal operation.
If routine inspections and regular maintenance work are performed as required, such failures can be avoided. (Siemens inverter repair example)
Siemens drive repair example 3: Siemens MM430 drive repair 11 kW
The static detection of the inverter module is normal and the rectifier module is damaged. (Siemens inverter repair example)
Measure the reverse resistance between PN within the normal range, and no abnormality was found in the main loop. The initial judgment was that the rectifier module was naturally aged and damaged.
However, in the process of cleaning and inspection, it was found that there were signs of component damage in the drive circuit, and further measurement of one component was damaged.
Causes the drive output to always be high. (Siemens inverter repair example)
Replace the rectifier module and repair the driver circuit.
The inverter suddenly has a damaged drive circuit during operation, which keeps the output high.
As a result, two inverter switching devices on the bridge arm are simultaneously turned on to form a short-circuit large current. The rectifier module is damaged first and loses high-voltage direct current to avoid damage to the inverter module. (Siemens inverter repair example)
Siemens inverter repair example 4: Siemens MM430 inverter maintenance 75kW
Static detection The inverter module is damaged and the rectifier module is normal. (Siemens inverter repair example)
Fault Analysis There is a trace of a damaged resistor.
Inverter module damage is mostly caused by damage to the driver circuit. Checking the drive circuit was indeed checked for a short circuit in the IOM resistor. 'This is a pull-up resistor at the output of the photo-isolated isolator 4506. This pull-up resistor damages the short circuit, making the input to the 4506, whether high or low, the output signal to the T95 is always high, which is Causes the WE and WE to be always high level, when the frequency converter is running, causes two switching devices of the same bridge arm to lead at the same time and damage the inverter module. Replace the resistor and drive the circuit to work. (Siemens inverter repair example)
The damage of this resistor is accidental. The exact cause of the damage is difficult to determine. It may be accidental spark burn. The greater possibility is the quality of the resistor itself. The reasons for the damage to the inverter module due to a short circuit in the resistor have already been discussed. In addition, the design of this circuit is that the pull-up resistor is connected to the output end of the 4506 photocathode isolator via a 47552 resistor, which protects the safety of the photo-isolator. Without this resistor, the pull-up resistor is directly connected to the output of the photo-isolator,
A short circuit in the pull-up resistor can cause damage to the photo-isolator. (Siemens inverter repair example)
Siemens inverter repair example 5: Siemens MM440 inverter maintenance 7.5kw
No symptoms are displayed. (Siemens inverter repair example)
Inverter high-voltage DC power supply is normal, the operating panel has no display, and there is no low-voltage DC power supply on the inverter control circuit.
The switching power supply circuit does not work. (Siemens inverter repair example)
It is detected that the voltage on the drain D of the switch tube VT is normal, and there is no pulse signal on the control electrode G but only a direct current voltage. This
UC3844 output signal is not normal, after inspection UC3844 damage, while the switch is also damaged.
Replace the UC3844, replace the switch, and the inverter returns to normal. (Siemens inverter repair example)
The failure to cut the fault is due to UC3844 output current after high damage, so that long-term conduction switch-like switch over-current caused by damage to the switch.
Siemens inverter repair example 6: Siemens MM420 inverter repair 7.5kW
F0003 (undervoltage) is displayed. (Siemens inverter repair example)
The frequency converter is connected to the power supply and the operating panel shows an undervoltage fault. The normal three-phase power supply voltage is measured, and the high-voltage DC power supply between the measurement PNs is also normal. This is a false undervoltage fault, the problem lies in the voltage detection protection circuit. First check the voltage sampling circuit. Figure 8-40 shows the resistor divider voltage sampling circuit. Measure 3 resistors, the resistance does not change basically, check the capacitor C3, dry and have more serious leakage phenomenon. Capacitor C3; welding, re-power,
The undervoltage fault display disappears and it is determined that the problem lies with the C3 capacitor.
Replace the capacitor and the undervoltage fault display no longer appears. (Siemens inverter repair example)
Siemens inverter repair example 7: Siemens MM440 inverter maintenance 22kW
Display F0003 (undervoltage) (Siemens inverter repair example)
The inverter is connected to the power supply, the operation panel displays the under voltage fault, the normal three-phase input voltage is detected, and the high-voltage DC power supply voltage is normal. It should be a problem with the voltage detection and protection circuit. First check the voltage sampling circuit, the resistance of the resistor is normal, the capacitance is normal, and the voltage sampling value is also normal (it can be calculated according to the resistor series voltage divider formula). The sampling voltage is sent to the HCPL788 IC and the output of the HCPL788 is low, and the input voltage is changed. The output voltage has no response.
Still low, indicating that the HCPL788 integrated circuit is damaged. Replace the HCPL788 integrated circuit and the under voltage display disappears.
Replace the integrated circuit HCPL788, inverter returns to normal. (Siemens inverter repair example)
After this inverter is powered up, an undervoltage fault indication appears due to the voltage detection protection circuit.
HCPL788 IC damage, its output voltage is always low, equivalent to the inverter under voltage, the sampling voltage drops to the specified value, HCPL788 IC corresponding output lower voltage value. After the CPU receives the under voltage alarm signal, it displays the under voltage fault code on the operation panel. (Siemens inverter repair example)
Siemens Drive Repair Case 8: Siemens MM440 Drive Maintenance 11 kW
F0002 'overvoltage' is displayed. (Siemens inverter repair example)
The inverter is connected to the power supply and the operating panel shows an overvoltage fault. The problem is usually in the voltage detection and protection circuit. Check the voltage sampling circuit in the resistor and capacitor are normal, and then check the amplifier circuit op-amp integrated circuit TL082 is damaged, the output always output high.
Replace integrated circuit TL082, fault elimination. (Siemens inverter repair example)
The amplifier circuit in the voltage detection and protection circuit amplifies the voltage sampling signal by a certain proportion. The core device in the amplifier circuit is an op amp integrated circuit. The drive integrated circuit adopted by this inverter is TL082.
TL082 is damaged and outputs a high level. This high level is an over-voltage signal. Therefore, after the CPU receives a signal reflecting overvoltage, it displays an overvoltage fault on the operation panel. (Siemens inverter repair example)
Siemens Drive Repair Example 9: Siemens MM440 Drive Repair 18 kW
Display F0072 (communication failure).
The inverter is controlled by the communication interface and shows internal communication failures. First connect from RS485 (Siemens inverter repair example)
In-port inspection, no abnormality in the signal transmission connection was found, and the filter was checked to be normal. When the level transfer chip 176B was checked, it was found that the operation was abnormal, and it was determined that the failure was related to the chip, so 75176B was replaced.
Replacing the 176B level transfer chip, the internal communication failure is eliminated and the inverter resumes normal operation.
When the level transfer chip 176B in the inverter is aged and damaged, the communication signal cannot be transmitted normally.
There is a communication failure signal. (Siemens inverter repair example)
Siemens Drive Repair Example 10: Siemens MM420 Drive Maintenance 11 kW
Display F231 output current unbalanced (Siemens drive repair example)
After the inverter is turned on, it displays the output current unbalanced fault. The fault is in the inverter output current detection and protection circuit or drive circuit. The output current detection and protection circuit of Siemens frequency converter MMV420 has 3 groups in total, the current is sampled in three-phase output current respectively. (Siemens inverter repair example)
The signal on the sampling resistor is amplified by the opto-isolator 7800A and then amplified by the integrated circuit
The TL084 amplifies it and sends it to the relevant circuit for processing as a current detection signal to the CPU. First check the 3 7800A
The working state, there are 2 7800A Vddl = IOV, and d = -5V, V0ut = OV, there are only 7800A Vddl = 20V,
With d=20V, vot=3V. The three voltages are not normal and obviously are fault conditions. (Siemens inverter repair example)
The 7800A's 4-pin voltage, which is connected to the VT, E pole, is also exactly 20V, the drive circuit's low-voltage DC power supply is also 20V, may be a negative voltage in the drive circuit zener diode Y4 damage short circuit, resulting in
VT. The E voltage Ue is equal to the low voltage DC supply voltage 20V. Check the zener diode Y; if it does damage the short circuit, check the zener diode Y again; the current limiting resistor in series also damages the short circuit. After replacing the resistor and Zener diode, the voltage of the 7800A returned to normal. (Siemens inverter repair example)
Replace the resistor and zener diode, F23' display eliminates.
This inverter has a bridge arm driving circuit power supply on the circuit, and the zener diode and the current limiting resistor are short-circuited, so that the output terminal Ue of the driving circuit is not a 5V voltage, but a voltage of 20V. Photocathode 7800A 4 pin is connected to the end, so the voltage on the 7800A4 footnote measured as 20V. 7800A 1 foot and 4 feet in series with a Zener diode VD, 4 foot voltage through the Zener diode VD is added to pin 1, so 7800A 1 pin voltage Udd l is also
20V (exact value is 19.4V). These two abnormal voltages make the output voltage of the 7800A not ov, but 3V, so that the output voltages of the three groups of current detection and protection circuits are inconsistent, and the inverter displays the imbalance of the output current measurement value. Actually, the unbalanced measurement value of the output current of the inverter is not caused by the fault of the current detection and protection circuit, but caused by the fault of the drive circuit. (Siemens inverter repair example)
Siemens inverter repair example 11: Siemens MM430 inverter repair 37kW
Display F231 "Unbalanced output current measurement" (Siemens inverter repair example)
After the inverter is turned on, the panel displays the imbalance of the output current measurement. First, the voltage values ​​of the three 7800A related pins were detected. No abnormality was found. The input voltages of the three operational amplifiers of the TL084 were all normal. The output voltages of the three operational amplifiers were found to be: 2 op amps. The output voltage is the same, and the output voltage of the other I op amp is significantly higher. It also checked its input resistance and feedback resistance and found no change in its value. Explain that this op amp circuit is damaged. After replacing the TL084, the output voltage of the three operational amplifier circuits is checked and the F231 display is eliminated. (Siemens inverter repair example)
Replace the operational amplifier TL084 and the inverter returns to normal. (Siemens inverter repair example)
Because one of the two 084s in the current detection and protection circuit is damaged, three input signals are the same and three output signals are different. Therefore, the operating panel displays the unbalanced fault of the output current detection value, and the fault is eliminated after the operational amplifier is replaced. . (Siemens inverter repair example)
Siemens Drive Repair Example 12: Siemens MM440 Drive Maintenance 22 kW
Display F231 (unbalanced output current detection value) (Siemens inverter repair example)
The fault is displayed when the inverter is connected to the power supply, which is usually the fault of the drive circuit and the current detection protection circuit. The 7800A input and output parameters can be detected first to determine whether the fault is in the driver circuit, the opto-isolated amplifier circuit, or the signal amplifier circuit. When checking the 7800A, it was found that there was a 7800A signal output pin 6 and pin 7 damaged open circuit, check the drive circuit found no abnormalities. Replace the 7800A and troubleshoot. (Siemens inverter repair example)
Due to aging damage of the 7800A optical isolator, the output signals of the three current detection and protection circuits are different, and the inverter shows that the output current detection value is unbalanced. (Siemens inverter repair example)
Siemens inverter repair example 13: Siemens MM420 inverter maintenance 37kW
There is an overcurrent fault record in the inverter's fault message. (Siemens inverter repair example)
The inverter is checked and running normally. Check the fault information memory for overcurrent faults.
Doubt about improper settings or load problems. Contact with the user, the user reported that the inverter suddenly stopped during normal operation.
Overcurrent fault is displayed. If it is restarted many times and it fails to rise to the operating frequency, an over-current shutdown will be displayed. Put another one inverter of the same model into operation. Explain that there is absolutely no problem with the load, nor is it a matter of setting the acceleration time. When the inverter is running with a load and the output current of the inverter is measured as 8A, the output current on the inverter's operating panel is already 15A. Obviously, there is a problem with the current detection and protection circuit. The output current sampling method of MM420 37kW inverter is using the resistance sampling method.
The sampling resistor string is in the output circuit and the voltage drop across the resistor is proportional to the output current. Check 3 sample resistance is normal, 3
A photo-occult isolator is also normal. (Siemens inverter repair example)
The inspection found that the feedback resistor value of the I group in the three groups of operational amplifier circuits became large, which increased the amplification factor of the amplifier circuit. This is the problem. After replacing the feedback resistor in the amplifier circuit, the output current value on the inverter's operation panel is consistent with the measured current value. (Siemens inverter repair example)
Replace the feedback resistor and the inverter returns to normal. (Siemens inverter repair example)
The output current in the frequency converter is taken out of the sampling circuit and the sampling signal proportional to itself is taken out, and then amplified by the amplifying circuit. The amplifying coefficient of the amplifying circuit is determined by the manufacturer according to the relevant parameters of the frequency converter and fixed by the circuit. The change of the feedback resistance value of the inverter is increased, so that the amplification factor of the amplifier circuit is also increased. The output signal voltage value reflects a much larger current than the actual output current, so that the output current is not a large frequency conversion The device issued an overcurrent fault message. (Siemens inverter repair example)
Siemens Drive Repair Example 14: Siemens MM420 Drive Repair 37kW
When the inverter is running, the displayed output frequency is not stable. (Siemens inverter repair example)
The user reflected that the output frequency of this Siemens MM420 37kW inverter was not stable during operation. To the site, the operating frequency set by this inverter was found to be 37.5Hz. After 37.5Hz, the 37.5Hz display disappeared 2^-3s and then appeared 34Hz. , and then slowly rose to 37.5Hz, stable for some time, and then repeat the above phenomenon. At that time, it was suspected that the large filter capacitor in the main loop was aging and the capacity was reduced. When the load was applied, the DC high voltage between PNs was unstable. Gradually reduce the load, reduce the output current, when the output current is reduced to 34A or less, the frequency display is stable, no longer disappear, fall and rise. (Siemens inverter repair example)
The corollary is that when the output current is small, the DC high voltage across the PN is relatively stable and the fault disappears. When replacing a circuit board composed of a new filter capacitor, failure cannot be eliminated, indicating that the problem is not here. And replaced by the control board on the normal inverter, the above phenomenon no longer occurs, of course, the problem is locked on the control board. Check the original control board found abnormal appearance of the small electrolytic capacitor, replace all the small capacitors on the control board, still installed to the faulty inverter, the inverter fault disappeared. (Siemens inverter repair example)
Replace the small electrolytic capacitor on the control board, so it is often ruled out. (Siemens inverter repair example)
The cause of the inverter's failure is not very clear, it may be caused by a variety of factors, and it is not easily detected, so we call it a "soft failure." When a “soft fault†is encountered, a comprehensive analysis can only be made based on the fault phenomenon, combined with the relevant knowledge and specific conditions of the inverter, to identify the possible causes of the fault, and then follow the priority one-by-one elimination method that is the most likely and relatively easy to handle. Treatment plan. The fault phenomenon of this inverter is that when the output frequency is high and the output current is large, the output frequency is unstable. When the output current of the load is reduced, the output frequency is stable, indicating that the fault is related to the load. This seems to be caused by the decrease in the capacity of the main loop filter capacitor. However, the replacement of the capacitor does not eliminate the fault, and the main control board is doubted. The small filter capacitor aging, when the DC high voltage between the PN slightly decreased, the aging of the small filter capacitor appears obvious side effects, CPU power supply is insufficient, it will cause work instability, the output frequency display instability of the failure.
Siemens inverter repair example 15: Siemens MM420 inverter repair 7.5kW
F002 alarm shutdown occurs during operation. (Siemens inverter repair example)
No abnormality was found in the static detection module, and normal power supply was also displayed. Check the fault memory there are many F002 (overcurrent) and F009 (undervoltage) fault records, found that the machine oil, dust more, in accordance with the repair routine before doing cleaning work, and then replace all the small electrolytic capacitors, and then install, The inverter is operating normally.
Cleaning and replacement of small-capacity electrolytic capacitors eliminates the malfunction of the inverter. (Siemens inverter repair example)
According to conventional over-current and under-voltage faults, the problem should occur in the current detection protection circuit and the voltage detection protection circuit. However, this inverter was only cleaned and replaced with a small-capacity electrolytic capacitor, and two types of faults were eliminated. This is because the oil and dust in the machine can damage the normal operation of some circuits. In addition, small-capacity electrolytic capacitors are also particularly prone to ageing, which can cause changes in some of the circuit's parameters and cause failures. (Siemens inverter repair example)
Siemens inverter repair example 16: Siemens MM440 inverter repair 17.5kW
Inverter power on indicates "1" flickering, sometimes only "1" (Siemens drive repair example)
Inverter shows "--is a form of undervoltage, it shows with "003" (Siemens inverter repair example)
The difference between the undervoltage fault alarm is that the former is the power supply voltage on the CPU such as the main control board is insufficient, but the control circuit can still work normally, the inverter stops outputting the display standby; the latter is the voltage is low to the control circuit can not work normally, The low voltage circuit works and the inverter stops outputting. Replace the main control board of the inverter with the same type and same power, the inverter display is normal,
The main body of the inverter is not faulty, but the DC power supply voltage on the main control board is low. Further inspection found that there was a trace of aging damage on the main control board with a small filter capacitor (105F/50V). Replace all the small filter capacitors on the main control board and other circuits. The display is normal and the inverter resumes normal operation. (Siemens inverter repair example)
Replace all the small filter capacitors on the main control board and other circuits.
The aging of the small electrolytic capacitor on the main control board of the inverter causes the DC power supply voltage of the main control board to be low, and a “-†fault phenomenon occurs. (Siemens inverter repair example)
Siemens inverter repair example 17: Maintenance of Siemens 6SE3222 75kW inverter Show F003, followed by F0050 (Siemens inverter repair example)
After the inverter is powered on, F003 is an undervoltage fault. Check that there is no abnormality in the high voltage DC voltage and the low voltage DC supply voltage, and check that the voltage sampling circuit is also normal. Check the integrated amplifier circuit TL084. The voltage is abnormal. After replacing the TL084, the display is normal. Press "RUN" key to run normally and the three-phase output voltage is balanced. After a few minutes, the F005 (overheating) is shut down, and the machine emits an odor, smoke, and immediately disconnects the power supply. Turn on the frequency converter to see the current-limiting resistor heating discoloration, it can be certain that the relay that short-circuited the current-limiting resistor does not move. Check that the relay is normal but the circuit supplying the relay has failed. It was checked that only one transistor in the power supply circuit was damaged. After replacing the transistor, the display is normal.
Replace the TL084 and the transistor, and the inverter fault is eliminated. (Siemens inverter repair example)
Inverter displays F003 because the integrated amplifier TL084 in the voltage detection and protection circuit is damaged.
The output signal is abnormal. An overheating fault occurs during operation due to the heat generated by the current limiting resistor. The direct cause of the current limiting resistor heating is that the relay does not operate. The failure of the relay power supply circuit is the root cause of the relay not operating. (Siemens inverter repair example)
Siemens inverter repair example 18: Siemens MM440 inverter repair 55kW
The speed cannot be adjusted, and the fault record shows "F0051" (read/write error when storing parameters). (Siemens inverter repair example)
Resetting the parameters according to the method described in the instruction manual failed to eliminate the malfunction. Turn on the frequency converter to see a lot of dust in the machine,
First clean the inverter thoroughly and replace the relevant capacitors. When the power is turned on, it works normally and the speed can be adjusted.
The F0051 fault display no longer appears. (Siemens inverter repair example)
Replacing aging-prone capacitors, cleaning printed circuit boards, and eliminating inverter faults.
The fault generated by this inverter is caused by abnormal CPU operation, low CPU power supply voltage, and CPU
Disturbances caused by work. Too much dust accumulates in the inverter. If the air is wet, it is easy to cause leakage in the internal circuit and to cause aging of the capacitor with a short life. This causes the DC supply voltage to be low and affects the normal operation of some circuits. Sometimes it also affects the normal operation of the CPU and other integrated circuits, which affects the normal operation of the entire machine. (Siemens inverter repair example)
Siemens inverter repair example 19: Siemens MM440 inverter maintenance 4kW
Fault F0022 is displayed. (Siemens inverter repair example)
Checking the user manual F0022 is a failure of the power module. Specifically, there are three contents, that is, DC loop overcurrent, brake chopper short circuit and ground fault. None of the three areas were found to be abnormal. It was found that the resistance value of the feedback resistor of the operational amplifier in the detection and protection circuit became larger, and the feedback resistor was replaced, and the F0022 fault display disappeared.
Replace the feedback resistor in the operational amplifier circuit and the inverter returns to normal. (Siemens inverter repair example)
The power component of this inverter is normal because the resistance value of the feedback resistor of the operational amplifier circuit in the protection circuit becomes larger, and the amplification factor of the amplifier circuit accordingly increases. The normal detection signal is enlarged by the amplifier circuit. Magnification of the magnification, the output signal reaches the amplitude of the fault signal, so the fault display signal F00220
Siemens inverter repair example 20: Siemens MM430 inverter repair 37kW
The rectifier module and the inverter module are normal and the power is turned on to display the F0005 (overheating) alarm. (Siemens inverter repair example)
When the inverter is powered on, there will be an overheat alarm, which is definitely a false overheat fault. The problem lies in the protection circuit.
After investigation, it was found that the solder joint at one end of the thermistor was off and the thermistor signal was not sent out. The resistance of the thermistor obtained by the protection circuit was infinite, and an error signal of overheating fault was issued.
Welding a good welding point, the inverter overheat alarm no longer appears, and is operating normally. (Siemens inverter repair example)
Siemens inverter repair example 21: Siemens 430 inverter maintenance 5.5kW
The user reports a communication failure. (Siemens inverter repair example)
The communication failure may be that the communication signal was not received, or the communication signal was not sent to the CPU.
Try to replace the other I drive, normal operation. The conclusion comes out. The problem lies in the signal transmission circuit of the communication interface to the CPU. After checking, the buffer chip A176 is damaged. Replace A176 chip, inverter communication is normal.
Siemens inverter repair example 22: Siemens 420 inverter maintenance 4kW
The power-on check fault record has an F0001 over-current alarm record. (Siemens inverter repair example)
Inverter over-current alarms mainly include normal over-current alarm caused by load overload and false over-current alarm caused by over-current protection circuit fault. After running with a load, it is found that the output current value displayed by the inverter is significantly greater than the measured output current value.
Obviously there is a problem with the current protection circuit. (Siemens inverter repair example)
It was further examined that the resistance of the current sampling resistor connected in series in the output circuit became large, resulting in the result that the sampling current was greater than the actual current.
Replace the original resistor with the correct resistance value of the sampling resistor. The problem is solved and the inverter is operating normally.
Siemens inverter repair example 23: Siemens 430 inverter maintenance 37kW
The user reports that the inverter has suddenly stopped during operation. A horizontal bar is displayed, and normal operation is resumed. The same fault occurs again after a while. The frequency of the fault develops from several days to several times a day. (Siemens inverter repair example)
The frequency converter appears this kind of breakdown phenomenon is probably because the control circuit power supply voltage is low, causes some chips to work abnormally.
The reason that the restart can still be performed after the shutdown is because the current is impacted during the restart and the voltage of the power supply rises.
The chip is in normal operation. The power supply voltage gradually decreases during the operation, causing the chip to work abnormally and shut down.
This phenomenon of making the control circuit power supply voltage low is caused by the leakage of the printed circuit board of the inverter caused by oil, dust, and moisture. At the same time, after the inverter is used for a long time, the aging of the small electrolytic capacitor, the decrease of the capacity of the capacitor, and the serious leakage phenomenon are the main reasons for the decrease of the power supply voltage of the control circuit. (Siemens inverter repair example)
For this fault, as long as the inverter is thoroughly cleaned, especially the printed circuit board, and all the small electrolytic capacitors are replaced, the problem will be solved. (Siemens inverter repair example)
Siemens inverter repair example 24: Siemens 440 inverter maintenance 15kW
The control panel of the inverter is running normally, and the external voltage control terminal cannot control the operation. (Siemens inverter repair example)
The control panel of the inverter is normal and the control of the external voltage control terminal is abnormal, which means that the inverter has no problem as a whole.
Only the voltage control circuit has a problem. The failure of the voltage control is due to the fact that the voltage-controlled control signal is not sent to the CPU. After checking that the 7805 regulator tube of the power supply is damaged, the 5V control voltage that the inverter should provide has no voltage value.
Replace the 7805 regulator, the control voltage is 5V, and the external voltage control function returns to normal. (Siemens inverter repair example)