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Navigate to NCK → Machine Data → Spindle Parameters in Siemens HMI. Review MD32010 (Leading Spindle 1), MD32020 (Leading Spindle 2), and MD32030 (Leading Spindle 3) to identify overlapping spindle assignments.

Do not modify MD parameters while spindles are running or coupled.

Check MD32110, MD32120, MD32130 (Following Spindle definitions for each coupling pair). Verify that no spindle appears as both a leading spindle in one coupling AND a following spindle in another active coupling simultaneously.

If overlap exists, redesign the coupling hierarchy to use only one active coupling chain at a time. Disable competing couplings using COUPLE(0) before enabling new couplings, or restructure MD parameters to reflect a single master-slave chain.

Chained couplings (e.g., Spindle1→Spindle2→Spindle3) are not supported; only star topology with one leading spindle is allowed.

Save corrected MD parameters and perform a full NCK reset (POWER ON/RESET cycle) to reload spindle coupling configuration before retesting.

Review the NC program around block %2. Search for COUPLE or COUPLE_SPIND commands. Identify which spindles are being coupled in what sequence.

Trace the coupling state: confirm that the following spindle designated in the new COUPLE command was not previously set as a leading spindle (via an earlier COUPLE command or via MD setup). Use the program simulation or single-block mode to step through coupling transitions.

Insert COUPLE(0) or explicit decoupling commands to release all spindles from their current couplings before establishing new coupling relationships. Ensure sufficient dwell time (G04 or time block) between coupling state changes to allow NCK synchronization.

Re-test the program using NCK trace (Diagnostics → Spindle Coupling Trace) to confirm coupling state transitions are sequential and non-conflicting.

Identify all active channels in the multi-channel system. Check the status display (HMI Channels menu) to determine which channels are running and what spindle couplings are currently active in each channel.

Review inter-channel synchronization logic in the part program (WAITM, CHGCHARTAB, channel switching commands). Confirm that channel %1 does not attempt to couple a spindle that is already claimed as leading by channel %2 or other active channels.

Implement channel serialization: use WAITM or channel synchronization points to ensure that only one channel can establish spindle couplings at a time. Decouple spindles in one channel before another channel attempts coupling of the same spindles.

Verify via HMI Diagnostics → Coupling Status display that each spindle is assigned to only one coupling relationship at any given time across all active channels.