For the A700 series, sometimes a UV (undervoltage) fault is encountered, and the rectifier circuit can be checked. The rectifier bridge of the A700 series 7.5kW or less inverter has a thyristor built in. The inverter is used to cut off the charging resistor during normal operation. The damage of the built-in thyristor will cause undervoltage faults. The damage of the switching power supply is also a common fault of the A700 series inverter. The common damage device is an M51996 waveform generator chip. The damage of this chip is usually caused by the sudden change of the working voltage. The most prone to problems are the power supply of the chip 14 pin, the 7-pin of the voltage reference value adjustment, the 5 pin of the feedback detection, and the 2 pin of the waveform output. In addition, in normal maintenance, it often encounters damage to the CPU board. Common fault alarms are E6 and E7, and the damaged devices are mainly concentrated on the program memory chips of the CPU board and some interface chips.