Three-phase power supply common fault repair

According to the test data of electric power experts, the power supply problem of computer interference and damage often occurs in the used power grid. Such as:

1. Power surges (high voltages generated when electrical equipment such as supercomputers, large-scale network servers, and switches are turned off);

2, high-pressure pulse (lightning, arc discharge caused);

3, wire noise (motor operation, relay action, broadcast launch, microwave radiation, etc.);

4, frequency offset (generator instability, small power supply frequency instability, etc.);

5. Continuous low voltage (startup of large-scale electrical equipment, application and main power line switching, etc.);

6. Mains interruptions (breaking of circuit breakers on lines, power interruptions, grid failures, etc.) These are the main factors that cause interference and damage to the computer. Failure to take effective protection measures in time will cause various degrees of damage to the computer and affect the hard disk. The normal operation of the floppy disk reduces the service life of the computer.

The emergence of power supply is undoubtedly the savior of electricity. It can not only make you useless when you suddenly lose power, but also can solve a lot of interference, so as to obtain a more pure power supply. The short-duration high-voltage spikes and high-frequency noise signals on the power line are effectively clamped to the minimum program, so that the stored data DATA and software programs in the computer system are not affected to ensure the normal operation of the computer or precision electronic instrumentation. .

Symptom: When the mains supply is normal, there is an output during the inverter, but the output voltage is high to 275V.

Analysis and maintenance: According to the working principle of regulated power supply, it can be seen that the above phenomenon will only occur when the high voltage protection circuit of the power supply and the mains voltage stabilization circuit have a fault. The output voltage of the power supply is sampled, rectified and filtered by T2, and then added to pins 8 and 9 of the voltage comparator U7, and then connected to the reference voltage terminal. Only when the voltage of pin 8 of comparator U7 is higher than the pin 9 voltage, pin 4 will jump into a low level output, thereby controlling the protection voltage action.

Fault phenomenon: When the utility power is interrupted, the inverter does not work, and the red indicator lights up for analysis and maintenance: According to the phenomenon of the fault, the fault is caused by the low battery voltage. Open the lid and measure the voltage across the battery at only 16.8v. After adding the electricity to the market, the voltage across the battery does not change, indicating that the fault occurred on the charging circuit. The working principle of the charging circuit is: when the utility power works normally, the main transformer T3 outputs the AC voltage of 25V, the output voltage of the pin 1 and pin 2 of the S2 relay outputs the voltage after the bridge rectifier of B1, C21, C22 and outputs 34v. DC voltage. After it is sent to the regulator U8 (MG317T) regulator, the battery is charged.

Symptoms: When the mains work, the power transformer noise analysis and maintenance: According to the phenomenon of failure can be seen when the transformer is overloaded, or the work of the state is unbalanced, unstable, it may send abnormal noise. However, we know that when the components connected to the transformer are damaged or some of the wires are in poor contact, it is possible to overload the load. Inspection of the secondary transformer did not find a short circuit between the contacts, inter-turn short circuit, and component damage. Wipe cleanly with alcohol cotton balls, and then pull out the plugs and sockets. After re-plugging, the noise of the transformer disappears and the UPS power supply is working properly. It is speculated that the cause of the malfunction may be too much dust on the circuit board, and a bad connection plug causes the transformer to be overloaded.

Fault phenomenon: In case of power failure, the inverter does not work. Analysis and maintenance: According to the analysis of the fault phenomenon, the fault is caused by the low battery voltage. Open the cover, remove it and charge it, and troubleshoot. After a period of time, the fault persists, so it is suspected that the charging circuit is faulty. Using a multimeter voltage file to detect the three-terminal adjustable voltage regulator block LM317 in the charging circuit, the input voltage is normal, but the output voltage is only 14.3v, no response to re-adjustment. Therefore, it is determined that the LM317 is damaged. Replace it, restart, remove the battery, adjust the charging voltage to 27v, the fault will be eliminated immediately.

Fault phenomenon: When the utility power is interrupted, the inverter does not work, and the buzzer sounds and analyzes and repairs: According to the fault phenomenon, the buzzer sounds long, indicating that the conversion control circuit of the power supply is normal and the inverter is not reversed. The change is due to the action of the protection circuit. Using a multimeter to check the battery voltage is normal, indicating that the fault is in the inverter circuit. The machine inverter circuit consists of pulse width modulator U1 (SG3524), sampling transformer T2, booster tubes Q5 and Q6, inverter Q17 and Q18. First, measure 10 feet of pulse width modulator U1 (SG3524) to see if it is locked (high level when locked), and then measure the resistance to ground when inverter tubes Q17 and Q18 are working statically. According to the data, when the black pen is grounded, the ground resistances of the e, b, and c of Q17 and Q18 are respectively 3.2 kΩ, 3.8 kΩ, and 0 kΩ; when the red pen is grounded, the resistances are 5.6 kΩ and 6.5 kΩ, respectively. 0Ω. Using a multimeter to measure the resistance values ​​of e, b, and c on the Q17 and Q18, all have a resistance of only 100Ω. At this time, it was found that the inverters Q17 and Q18, and the propulsion pipes Q5 and Q6 were all burned out. Replace it, troubleshooting.

Symptom: When the mains power supply is normal, it works normally; when the mains electricity is cut off, no 220v voltage output is accompanied by long-sounding alarm sound analysis and maintenance: According to the fault phenomenon, carefully check the battery voltage is 26V, normal; two inverters The high power output tube and the corresponding driver are also normal. It is estimated that there is a problem with the battery voltage detection circuit. Under normal circumstances, the 6th leg voltage is the reference voltage and maintains at about 1.2v; when the battery is at the normal value of 26v, the calculation shows that the 7-pin voltage is about 1.4v, so the 1 pin voltage is 12v high. The UPS is now placed in a no-mains-operated state and the feet 1, 6, and 7 of IC1 are measured. The voltage values ​​are 0v, 1.2v, and 0v, respectively. From this, it can be seen that the voltage of pin 7 is low. From this, it is inferred that R3 and R4 have partial pressure problems. Measure the resistance of R3 and R4 respectively and find that R3 has been disconnected, replace it, and troubleshoot.

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