If after completing Steps 1–5 you still see the error with a stable "6" on the NCU, suspect a dead NCK processor or failed backplane. At this age, repair may exceed the value of the control. Consider:
The "Waiting for NCK Connection" error on a SINUMERIK 810D is seldom a single-point failure. It is a symptom of a broken handshake between the HMI and the NCK. By methodically checking the NCU’s hardware state (7-segment display), isolating the Profibus, verifying batteries, and restoring from backup, 90% of these faults can be resolved without a service call. However, given the 810D’s age (end-of-life since 2005), repeated occurrences should prompt a serious discussion about control upgrade. sinumerik 810d waiting for nck connection
Final checklist before restart:
| LED | State | Meaning | |-----|-------|---------| | SF (red) | ON | NCK not ready / system error | | SF (red) | Flashing | NCK booting or waiting for PLC | | 5V (green) | OFF | No logic power | | NC (green) | OFF | NCK not active (should be ON steady) | If after completing Steps 1–5 you still see