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Check the UPS (Uninterruptible Power Supply) status and event logs. Verify power supply continuity to the PC-NC controller and ensure the 24VDC backup battery for the Real-Time Kernel is functional.

Do not immediately restart the machine. Allow at least 60 seconds before power cycling to ensure all capacitors discharge.

Navigate to Diagnostics > System Information > Memory in the SINUMERIK 840D HMI to view the FFS backup timestamp. Compare this against operator records to identify which changes were lost since the last successful backup cycle.

Review the NC program and MD parameter modification history. Manually re-enter any critical parameter changes (focus on tool offsets, workpiece offsets, and axis-specific MDs like MD1000-MD1099 for axis configuration) that occurred after the backup timestamp.

Execute a controlled FFS backup by navigating to System > Backup & Restore > Backup FFS to ensure a fresh backup copy is created and validated before resuming production.

Access the NCK diagnostics menu: Diagnostics > System Information > Memory Status and check for reported error codes in the flash memory controller logs. Look for entries indicating 'Backup Medium Read Error' or 'FFS Checksum Mismatch' with specific sector addresses.

Run the Siemens SINUMERIK Diagnostics Tool on a connected engineering workstation. Connect to the 840D controller and execute a Full Memory Self-Test (FMST) to scan all FFS sectors for read/write failures and uncorrectable bit errors.

This test may require 30-45 minutes and should be performed during scheduled maintenance windows only.

If FMST reports multiple sector errors in the FFS, contact your Siemens field service depot to schedule flash memory module replacement. Do not attempt repeated power cycles, as this accelerates wear on degraded sectors.

Verify backup medium accessibility by navigating to System > Storage Devices in the SINUMERIK HMI. Confirm that the backup medium is detected, mounted, and shows sufficient free space (minimum 10% of FFS size). Check for any 'Medium Not Ready' or 'I/O Error' messages.

Manually initiate a backup-to-medium operation: System > Backup & Restore > Backup FFS to Backup Medium. Monitor the progress bar and verify completion with a confirmation message. If the operation times out or fails, record the error code.

Ensure no NC programs are running and no parameter writes are in progress before starting the backup.

If backup fails, examine the system logs by accessing Diagnostics > System Messages > Error Log and filtering for 'Backup' or 'FFS' keywords. Cross-reference error codes against Siemens SINUMERIK documentation. If backup medium errors persist, replace the backup medium (CompactFlash card, USB drive, or secondary flash module depending on your hardware configuration).