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Check the CNC operator panel for recent key reset or emergency stop activation during synchronized spindle threading or tapping operations. Review the alarm log timestamp correlation with operator actions in the HMI interface.

Verify spindle synchronism parameters: Check MD 33050 (SPIND_SYNCH_MODE) and MD 33051 (SPIND_SYNCH_TOL) in the NCK Machine Data editor (Diagnostics > Machine Data > Spindle). Ensure synchronism tolerance is appropriate for your application.

Review the G-code block execution history in the NC buffer (Diagnostics > NC > Program Execution State) to confirm which block triggered the synchronism loss. Check for any FLIN/FSYN command syntax errors.

Do not reset alarms until root cause is identified; repeated resets indicate persistent machine configuration issues.

If key resets are occurring during normal operation, check the PLC input mappings (OB1 cycle time and PLC watchdog parameters MD 7010) to ensure the control loop is not being triggered by electrical noise or timing conflicts.

Access the Diagnostics > Spindle > Spindle Override display to verify real-time override values during synchronized operation. Check if override values are erratic, zero, or outside the 0-200% range during synchronization attempts.

Inspect Machine Data parameters MD 35070 (MAX_OVERRIDE_FO=200%), MD 35080 (MIN_OVERRIDE_FO=0%), and MD 32020 (FLIN_RP, ramping rate) using the NCK editor. Verify these are set correctly for your machine tool's spindle rating.

Review the PLC source code (OB1 or spindle synchronism subroutine) for any dynamic override calculations or HMI-to-NCK variable mappings. Check for uninitialized variables or division-by-zero conditions that could generate invalid override commands. Use the Diagnostics > PLC > Variables view to monitor real-time override variable changes.

Test the synchronization function with fixed 100% feed override (no HMI dynamic adjustment) to isolate whether the issue is caused by override calculation logic or by the synchronism mechanism itself.

Check spindle encoder connectivity and signal quality: In Diagnostics > Spindle > Encoder Feedback, verify the encoder pulse count increments smoothly during spindle rotation. Look for signal dropout or stuck values indicating a hardware connection issue.

Encoder signals should update at least once per machine cycle. Frozen values indicate electrical disconnection.

Review the Spindle Synchronism Tolerance parameter MD 33051 (SPIND_SYNCH_TOL, typically 0.5–2.0° for tapping). If the value is too tight relative to your spindle inertia and servo response, the synchronism loop will continually fault. Increase the tolerance incrementally and re-test.