16688

Navigate to Diagnostics > Parameters > Machine Data (MD) and locate MD 37100 (Spindel_Kopplungstyp_Nummer) and MD 37110 (Spindel_Kopplung_Typ_Definition) for the affected coupling. Count the number of master axis/spindle entries in the coupling definition.

Do not modify parameters while an active program is running; use EMERGENCY STOP first.

Review the coupling configuration in the NCK menu: Diagnostics > Machine > Spindle Couplings. Verify the number of assigned master values does not exceed the system limit (consult machine-specific documentation for your 840D variant).

Reduce the number of master axes/spindles in the coupling by removing redundant or unnecessary entries. Edit MD 37110 et seq. to delete duplicate master references, or split the coupling into multiple coupling instances if functionally required.

Changes to coupling definitions may affect active part programs; coordinate with production planning.

Verify the corrected coupling configuration by re-entering the part program block that triggered the alarm. Monitor the Diagnostics > Alarms log to confirm alarm 16688 no longer appears.

Examine the NC block (%2 in alarm message) in the part program editor. Identify any COUPDEF, COUPLE, or spindle master-assignment G-codes. Cross-reference the coupling type number or identifier against the configured couplings in Diagnostics > Machine > Spindle Couplings.

Verify that the coupling type referenced in the G-code exists in MD 37100. If the coupling type is missing or has a typo, correct the part program to reference a valid, pre-configured coupling type that does not exceed master value limits.

If the coupling must include all specified master axes, request a new coupling definition from your machine builder or Siemens FAE; existing coupling instances may not be modified once active.

After correcting the part program or confirming the coupling type is valid, reset the alarm (ALRM_ACK in HMI or via PLC input) and restart the block.

Perform a soft reset of the NCK: use Diagnostics > System > Reset NCK (or equivalent menu on your HMI variant). Do not clear all machine data; this will reload coupling definitions from non-volatile storage.

Soft reset will interrupt any active program; ensure machine is safe.

If the alarm persists, initiate a parameter reload: Diagnostics > Parameters > Load Machine Data from Backup. This forces the system to re-validate all MD entries, including coupling configurations.

Parameter reload may take 2–5 minutes; do not power-cycle during this operation.

Verify the coupling configuration is intact by reviewing MD 37100–37199 in the Parameters menu. If any values appear corrupted (e.g., out-of-range entries, missing sequential indices), contact your Siemens Service partner to restore from a known-good backup.

After restoration, re-run the part program block that triggered the alarm. If alarm 16688 recurs, escalate to Siemens field service for memory diagnostic testing.