A: 1. Check the fault history and current alarms. Review the historical fault records on the HMI, as they may reveal the root cause of the POFF condition.

2. Verify control and auxiliary power supplies. Ensure all low-voltage circuit breakers and switches in the control cabinet are closed. If a UPS is present, check its operational status. Alternatively, open the VFD control cabinet door and observe whether indicator lights for all power modules (e.g., PLC power supply, trigger power supply, drive board power supply) are lit normally (typically green indicates normal operation).

3. Verify all interlock and safety signals. An unclosed safety interlock circuit will force the system into POFF. Check external safety interlock signals on user terminals—including emergency stop, remote/local switch, fan fault, and transformer overtemperature signals—to ensure they are in normal state (typically normally open or normally closed contacts). Simultaneously confirm all cabinet doors (switchgear, transformer, control) are fully closed.