28010

Verify physical connectivity: Inspect PROFIBUS/PROFINET cables between NCUs for damage, kinks, or loose connectors. Check cable shielding continuity and ensure proper grounding at both ends per IEC 61158 standards.

Power down the control cabinet before inspecting connectors to avoid electrical hazard.

Access Diagnostics menu: Navigate to NCK → Diagnose → NCU Link in the operator panel or HMI. Monitor message transmission/reception counters and error counters for the NCU link to identify if errors correlate with alarm occurrences.

Check MD 32100 (NcuLinkCycleTime) and MD 32101 (NcuLinkTimeout): These parameters define the NCU link cycle time and timeout threshold. If timeout is set too aggressively (e.g., < 50ms), increase it incrementally and monitor. Typical range is 50-100ms.

Excessively large timeout values may degrade system responsiveness; consult machine documentation.

Verify remote NCU status: Check the LED indicators on the remote NCU control module (typically located on the 840D front panel). A solid red LED or no LED activity indicates the NCU is offline or in fault state. Cross-reference with the system alarm list on that NCU.

Perform a controlled power-cycle reset: Switch off the machine emergency stop or main contactor, wait 10 seconds for capacitors to discharge, then restore power. Allow full 60-90 second startup sequence. Monitor both NCUs reaching 'Ready' state before resuming operation.

Ensure all axes are in a safe, parked position before power cycling to prevent unintended motion.

Check remote NCU PLC program execution: In STEP 7 or TIA Portal, access the remote NCU's PLC diagnostics and verify the OB1 (main cycle) is running without errors. Review recent runtime errors in the PLC log. If PLC has halted, upload a fresh compile or check for corrupted NVRAM (MD 31000 - MemoryMode).

Validate NCU link table configuration: Open HMI menu Parameterize → NCU Link and confirm that the communication table number in MD 32050 matches the table referenced on the remote NCU. Both NCUs must have identical message structure definitions (data types, offsets, lengths).

Verify NCU link enable flags: Confirm MD 32060 (NcuLinkEnable) is set to 1 (enabled) on both the local and remote NCU. Check that no safety interlocks or soft-disable conditions are preventing NCU link activation via the PLC OB1 program.

Cross-compile and reload PLC program: If parameter values were recently changed or updated, recompile the PLC project in STEP 7 and download to both NCUs. Inconsistent symbol definitions between compile cycles can cause interpretation errors in inter-NCU messages.