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Open the active part program in the Program Editor (NCK Menu → Program) and locate the CYCLE73/74/75 call block referenced in the alarm message (block %2).

Verify that _TN is declared before the cycle call with a valid tool number assignment, e.g., '_TN=5' or '_TN=_TOOL' where _TOOL is a previously defined variable.

Ensure _TN contains an integer value matching an existing tool in the tool management table (Tables → Tool Data in Siemens control interface).

Check the cycle syntax in the part program matches SINUMERIK documentation: CYCLE73(…, _TN, …) with proper parameter order and delimiters.

Reload and execute the corrected program from the beginning to verify alarm clears.

Navigate to Tables → Tool Data (or Siemens TM menu) and verify the tool number specified in _TN exists as an active record.

Check that the tool status is 'active' (not 'reserved' or 'broken') in the tool management status column.

Confirm the tool offset record contains populated geometry fields: tool length (_L), tool radius (_R), and any cycle-specific parameters required by CYCLE73/74/75 (e.g., flute count, feed rates).

If the tool record is missing or incomplete, create or update it using the Tool Editor. Ensure all mandatory offset values are non-zero and within valid ranges per SINUMERIK documentation.

Save the tool table (typically via File → Save or Ctrl+S in Tool Editor) and restart the part program execution.

Access Diagnostics → Machine Data (MD) menu and verify MD30200 (Tool management active) is set to '1' (enabled) and MD30210 specifies the correct tool table source (T, D, or combined T+D format).

Consult your machine builder's commissioning documentation for correct MD30200/MD30210 settings specific to your control configuration.

Check MD32010 (Tool offset data source location) and confirm the tool table file path points to the correct working directory. Verify the file exists and is readable by the NCK process.

Review SD54020 (Active tool table name) to ensure it matches the filename in the part program's LOAD_TOOL or default tool table reference.

If MD parameters were corrected, save them, perform a full control restart (via Siemens HMI or hardware reset), and retry the part program.

Machine data changes require proper authorization and may necessitate re-commissioning of servo and safety parameters; contact your Siemens service representative if unsure.