Cause : CB Warning 8 comes when there's an issue with the communication settings or configuration between the inverter and the device it's communicating with, typically a Programmable Logic Controller (PLC) or a Human-Machine Interface (HMI).

A0707 alarm in Siemens Micromaster 420 indicate a communication board (CB) warning 8. This indicates an issue with the parameters or configuration settings on the communication board.

Resolution:

1. Refer to the Communication Board User Manual: The specific cause and resolution steps will depend on the type of communication board you're using with the Micromaster 420. Consult the user manual for the communication board itself. This manual should provide details on interpreting the specific CB warning code and the recommended corrective actions.
2. Verify PROFIBUS Configuration (if applicable): If you're using PROFIBUS communication, double-check the configuration settings on both the PROFIBUS master device and the Micromaster 420. Ensure they match and are set up correctly.