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Check the tool magazine for mechanical obstructions, chips, or debris preventing proper indexing. Manually rotate the magazine through several positions to verify smooth movement.

Ensure machine is in a safe state and axis drives are disabled before manual manipulation

Verify magazine position encoder or proximity switches are functioning correctly. Check PLC inputs for magazine home position and current pocket position signals in the PLC diagnostics screen.

Review the tool management data (magazine configuration) and verify the target pocket number is valid and not marked as disabled or blocked in the tool magazine table.

Execute a magazine reference point approach (magazine homing) cycle to re-establish correct position feedback, then attempt tool unload again.

Check pneumatic or hydraulic pressure supply to the tool changer system. Verify pressure gauges show nominal values (typically 5-6 bar for pneumatic systems). Listen for air leaks.

Inspect tool gripper fingers for damage, wear, or contamination. Verify the gripper opens and closes fully by observing PLC outputs and corresponding sensor inputs during manual tool change operations.

Use manual tool change mode with reduced speed for safe observation

Check all tool changer limit switches and proximity sensors (arm extended, arm retracted, gripper open, gripper closed, tool clamped) in PLC diagnostics. Replace faulty sensors showing inconsistent signals.

Verify the tool is properly seated and released in the spindle. Check spindle orientation (M19) completes correctly and drawbar releases tool (unclamping signal active). Test with spindle blow-through to ensure tool releases freely.

Access PLC diagnostics and review the tool change sequence status bits and timers. Identify which step in the unload sequence failed by checking the last active step marker before alarm generation.

Review alarm log history and NC/PLC interface signals (VDI/DB31-DBB3 area) to identify missing handshake signals between NC and PLC during tool change. Look for 'tool change acknowledge' or 'magazine ready' signal discrepancies.

Check for recent PLC program modifications or parameter changes in the tool changer function blocks. Verify timeout values are appropriate for the machine's mechanical response times (typically 5-15 seconds per operation).

Perform a controlled tool change test in single-step mode via PLC diagnostics to isolate the exact failure point. Monitor real-time I/O and verify each mechanical motion completes before proceeding to next step.

Ensure safe distance from tool changer mechanism during single-step testing