F7403 fault in Siemens V70 Drive indicates the Lower DC link voltage threshold was reached. This means the internal DC bus voltage dropped below the required operating level while the drive was running, usually caused by a dip in the main supply voltage.
Cause: The DC link voltage monitoring is active and the lower DC link voltage threshold was reached in the “Operation” state.
Remedy:
- Check the line supply voltage.
- Check the infeed.
- Reduce the lower DC link threshold.
- Switch out (disable) the DC link voltage monitoring.
