A: 1. First, check if the bus voltage is normal and if the input and output fuses are functioning correctly.
2. Check for other accompanying alarms. Refer to the service manual to check the rectifier IGBT, bus fuse, and inverter IGBT.
3. Carefully inspect the fan outlet for corrosion, including the rectifier board J11 and inverter board J18 interfaces, and the location of the bus fuse.
4. Check if the signal cables connecting to the control board are properly connected.

Solution: 
1. Replace the rectifier board, bus board, and inverter board based on the inspection results and corrosion findings.
2. Replace the signal cables and control board.
(When replacing the control board, take precautions against static electricity and apply hot melt glue to the signal cable connections.)