Inverter switching power supply repair method
1. Several maintenance steps of switching power supply are as follows:
1. Check whether the rectifier circuit D1-D4 is broken down or whether the capacitance of the circuit breaker filter circuit is damaged, whether the balance resistors R1 and R2 are normal, whether the step-down resistor R3 is burnt out or the resistance value increases and fails (test when power is off).
2. Detect whether the b-e junction and c-e junction of the switching tube have a breakdown short circuit phenomenon, and measure whether there is a short circuit phenomenon in each winding of the switching transformer to determine whether the switching tube and the switching transformer are good or bad (test when the power is off).
3. Detect the rectification and filter components of the secondary output winding, and focus on checking whether the filter capacitor is swollen or damaged, so as to rule out the possibility of a short circuit in the secondary circuit.
4. Check whether the absorption circuits D5, R11, and C9 are normal (test when the power is off).
5. In the case of confirming that the above components are normal, we can remove the switching power supply board from the inverter and conduct a power-on test on it separately. Use a voltage regulator to slowly adjust to the rated voltage of the switching power supply. At this time, you should hear the squeaking sound of the transformer when it starts to vibrate. If you do not hear the sound of starting the vibration, use a multimeter to detect the positive and negative voltage of the UC3844 power supply. Whether there is a DC voltage of about 12V-16V between them.
6. After confirming that the voltage of the power supply terminal of UC3844 is normal, you can use an oscilloscope to check whether there is a PWM wave output to the trigger terminal of the switch tube at pin 6 of UC3844 (according to different circuit designs, the frequency of PWM wave is generally between 20KHZ-100KHZ) .
7. If there is no PWM wave output, replace timing components C5, R8, C6 or UC3844. After the elimination of the above steps, the switching power supply should be able to work normally. In the frequency converter, there are many types of switching power supplies, but the basic principles are the same. For example, each PWM management chip has a power supply terminal, a timing component RC network, and a port for outputting PWM waves. As long as we understand their work According to the principle, according to certain methods and steps, the fault can be eliminated.
2. Problems encountered in actual maintenance and solutions:
1. Delta inverter (fault phenomenon: no display when power on)
After testing, it was found that the main circuit of the power supply, the charging resistor, and the contactor of the main circuit were all normal, so it was determined that the switching power supply board was faulty. Follow the repair steps above to measure the switching power supply board. During the first step of measurement, it was found that the 330KΩ/2W step-down resistor between the DC bus 560V and the PWM modulation chip was damaged. The nominal resistance of 330KΩ/2W actually measured more than 2MΩ. Therefore, the PWM modulation chip must be damaged. To start the power supply, so can not start to work. For the sake of caution, key components such as switching tubes, transformers, rectifier diodes, and filter capacitors were tested. After confirming that there is no problem, power-on test, OK! The switching power supply starts to oscillate, and the output voltages of each group are normal. After the inverter is installed back, the start-up test is normal, and the inverter has been repaired (Note: maintenance personnel must form a habit during maintenance: do not rush to replace the test machine after finding bad components, Be sure to test all the high-power and easily damaged components, and test the machine after confirming that there is no problem, which is both safe and secure).
2. Taian inverter (fault phenomenon: no display when power on)
After testing, it was found that the main circuit of the power supply, the charging resistor, and the contactor of the main circuit were all normal, and the fault was determined to be on the power board. Follow the repair procedure to measure the switching power supply board.
The first step of measurement passed. During the second step of measurement, it was found that the c-e junction of the switch tube was broken down. It was removed, and then the transformer, rectifier diode, filter capacitor and other key components were tested. The voltage is normal, the installation test is normal, and the fault is eliminated.
3. Siemens inverter (fault phenomenon: no display when power on)
After testing, it was found that the main circuit of the power supply, the charging resistor, and the contactor of the main circuit were all normal, and the fault was determined to be on the power board. Follow the repair procedure to measure the switching power supply board.
The first step of measurement passed, the second step of measurement passed, the third step of measurement passed, the fourth step of measurement passed, and then power on the power board alone to measure the voltage of about 12.5V from the power supply end of the PWM modulation chip to ground, indicating that the power supply is normal . Look at the PWM output terminal of the chip with an oscilloscope, and find that there is no PWM modulation waveform. After replacing the PWM modulation chip, the power-on test is normal, and the fault is eliminated.
4. Schneider inverter (fault phenomenon: no display when power on)
It was found that the main circuit of the power supply, the charging resistor, and the contactor of the main circuit were all normal after testing the repeatedly burned switch tube, and the fault was determined to be on the power board. Follow the repair procedure to measure the switching power supply board.
The first step of measurement passed, the second step of measurement found that the switch tube breakdown, the third step of measurement passed, the fourth step of measurement passed, replaced a new switch tube, and powered on the power board separately, the tube burned again. Remove the switch tube without installing the tube, conduct a power test, and measure that the power terminal of the PWM modulation chip has a voltage of about 12V to the ground, which is also normal. Use an oscilloscope to look at the PWM output of the chip, and find that the PWM wave is only about 5-6 KHZ. After the power is turned off, the timing component is removed and measured. It is found that the resistance of the timing resistor becomes larger. Burn the power tube, troubleshooting.
5: Lenz inverter (fault phenomenon: no display when power on)
Repeatedly burned switching tubes are measured on the switching power supply board according to the maintenance steps.
The first step of the measurement passed, the second step of the measurement found that the switch tube c-e junction breakdown, the third, fourth, fifth, sixth, and seventh steps all passed the measurement. Install a new switch tube and power on the test. As the voltage of the voltage regulator increases, you can hear the squeaking sound of vibration, but it is a little loud. After the voltage is adjusted to the rated voltage, the measured output voltage is lower than the normal value. After 2 minutes, I suddenly smelled a burning smell, and the fuse broke. I quickly turned off the power and found that the switch tube was very hot, and the measurement found that it had broken down. Remove the switch tube and conduct a power-on test. Measure the voltage of the power terminal of the PWM modulation chip to the ground at about 12V. Use an oscilloscope to look at the PWM output terminal of the chip. It is found that there is PWM wave output and the frequency is about 30 KHZ, which is also normal. Therefore, I suspected that the quality of the switching tube just changed was not good, so I replaced it with another one, and after powering on the test, the tube was burned again. After the power was turned off, I accidentally touched the components of the absorption circuit and found it hot, but it was normal during the measurement. Ah, so I tested it again, and it was still normal. Simply dismantle the absorption circuit first, and replace it with a tube for power-on test. It is found that the squeaking sound of the transformer is small, and the output voltage of each group is also normal. After running for 20 minutes, the switch tube did not burn again. After the power was turned off, the switch tube became slightly hot when touched, which was a normal heating state. Therefore, it was judged that the fault was in the absorption circuit. Replace the components of the absorption circuit, and the fault was eliminated.
