27900

Inspect all PROFIBUS DP connectors on the affected axis drive and NCK module for corrosion, bent pins, or loose M12 connectors. Check cable routing to ensure separation from motor power lines and inverter output cables by at least 150mm.

Do not test PROFIBUS continuity with high-ohm meggers; use only low-voltage multimeters or qualified PROFIBUS test equipment.

Verify 120Ω termination resistors are installed on the PROFIBUS DP network—typically at the NCK interface module and the last drive on the line. Access the physical termination switches on each device's DP connector.

In SINUMERIK HMI or Siemens SCOUT TIA, navigate to Diagnostics → Communication → PROFIBUS and check the error counter for this axis. Log the code %2 value (typically 0x80xx range for SI faults) and correlate with SINAMICS drive error logs via STARTER tool.

Replace the PROFIBUS cable segment with certified CAB PB (shielded twisted-pair, 0.34 mm²) and re-terminate. If alarm persists, swap the DP interface module (typically located in the NCK control cabinet) and test.

Access the affected drive via SIEMENS STARTER software and retrieve the detailed SI fault code from the drive's diagnostic buffer. Code %2 in alarm 27900 typically maps to drive error classes (e.g., 0x8101 = encoder loss, 0x8201 = parameter error). Document the exact fault code.

In SINUMERIK NCK, navigate to Axis-Specific Parameters → [Axis name] → Drive Assignment and verify that MD33000 (Encoder type) and MD33005 (Encoder resolution) match the physical encoder on the drive. Cross-reference against the SINAMICS drive type (S120, S210, S210P) documentation.

Check PROFIBUS address assignment: in SINUMERIK, verify that the drive's PROFIBUS slave address (typically set via DIP switch on the DP interface or via STARTER) matches the PROFInet/PROFIBUS node configuration in the NCK. Misalignment causes the drive to reject servo commands.

In STARTER, perform a parameter backup, then reset the SINAMICS drive to factory defaults, reload the saved parameters, and perform a commissioning reset (parameter set P0970=1). Perform an axis power-on and reference move to confirm SI fault clears.

Resetting drive parameters may disable safety-critical settings; ensure machine is in a safe state and all personnel are clear before recommissioning.

In SINUMERIK HMI, navigate to System Information → Software Versions and document the NCK kernel version (e.g., 6.40.02) and the PROFIBUS interface firmware. Cross-reference against Siemens release notes to confirm compatibility with the SINAMICS drive firmware version (retrieved from STARTER).