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Verify RESET source: Check PLC variable NC_RESET (or NC_RESET_COMMAND in Operate mode) in the Diagnostics > PLC > Input/Output menu to confirm RESET was intentionally triggered.

Review NC program flow: Confirm whether the RESET was expected (e.g., end of program, operator intervention). Check program structure and M02/M30 commands which trigger automatic RESET.

Inspect $AA_TOFF state before RESET: Use MDI to query the offset value with command 'MSG $AA_TOFF' or monitor via Machine > Tool Management > Current Offsets in the HMI before executing RESET.

Check PLC source code (via Siemens STEP 7 / TIA Portal): Search for NC_RESET assignments in the main PLC program, especially in fault handlers or cycle logic. Verify reset conditions are guarded with proper interlocks.

Review machine parameter MD20200 (RESET_MODE_MASK) in Diagnosis > Machine Parameters > Spindle/Tool to confirm offset clearing behavior on RESET is as designed. Document expected reset behavior.

Audit operator actions: Check system log timestamps (Diagnosis > System Diagnostics > Alarms) to correlate RESET alarm with operator button presses or program M-codes executed just prior.

Review program structure post-RESET: Confirm NC program includes tool selection and offset compensation commands after program restart. Check for missing T-code or G43 equivalent in program initialization block.

Verify tool offset table in Diagnosis > Machine Data > Tool Management (MD parameter range 32500-32999): Ensure correct tool length offsets are loaded and accessible to the channel. Cross-reference with tool magazine inventory.

Test tool offset reactivation: Execute a manual tool selection (T<tool> M06) in MDI mode after RESET and verify $AA_TOFF is re-populated. Monitor via HMI diagnostics display.