330-003D

Check Key Switch Position

Verify the detachable key switch positions match the displayed operating mode in MOD function. Check switches for positions 2 (input 18), 3 (input 11), and auxiliary switch (input 19).

Always follow lockout/tagout procedures when checking key switches

Test Switch Continuity

Using a multimeter, test continuity across key switch contacts while cycling through positions. Check for intermittent connections or worn contacts.

Key switches often fail at detent positions - test multiple times at each position

Verify Safety Module Inputs

Access PLC diagnostics and monitor safety inputs 11, 18, and 19 in real-time while operating key switches to identify signal discrepancies.

Use the TNC's integrated PLC status display for real-time monitoring

Replace Defective Switch

If switch shows intermittent behavior or failed continuity, replace with identical Heidenhain-approved key switch and reconfigure safety parameters.

Safety switch replacement requires safety system validation and may need certified technician

Visual Inspection of Safety Connectors

Power down system and inspect connectors X65, X66, and X67 for loose pins, corrosion, or physical damage. Check connector seating and locking mechanisms.

Ensure complete power isolation before connector inspection

Measure Signal Continuity

Using wiring diagrams, measure continuity from safety module inputs to their respective sources, focusing on inputs 4, 8, 10, 11, 18, and 19 mentioned in alarm description.

Check both signal and return paths - safety circuits are typically dual-channel

Check Cable Routing and Shielding

Verify safety cables are properly routed away from power cables and that shielding is intact and properly grounded to prevent EMI interference.

Safety cables should maintain minimum 6-inch separation from motor power cables

Reseat and Secure Connections

Clean connector contacts with appropriate contact cleaner, reseat all safety module connectors, and verify proper torque on terminal connections per Heidenhain specifications.

Use only approved contact cleaners that won't leave residue

Check Safety Module Status LEDs

Examine all status LEDs on the safety module for error indications. Red LEDs typically indicate faults, while green indicates normal operation.

Refer to safety module manual for specific LED pattern meanings

Perform Safety Module Diagnostics

Access TNC safety diagnostics menu and run built-in safety module tests. Check for any reported internal faults or communication errors.

Safety module diagnostics may temporarily disable safety functions

Compare Input/Output States

Monitor safety module inputs and outputs simultaneously to identify any processing delays or incorrect logic operations within the module.

Use oscilloscope for timing analysis if available - safety modules have strict timing requirements

Replace Safety Module

If diagnostics confirm internal failure, replace safety module with identical part number and restore safety configuration from backup or manual reconfiguration.

Safety module replacement requires complete safety system validation and certification

Check Velocity Feedback Signals

Monitor encoder feedback signals for axes and spindle to ensure clean, consistent velocity data is reaching both CC and MC controllers.

Use TNC's built-in encoder diagnostics in the service menu

Verify Safe Velocity Parameters

Check machine parameters related to safe velocity limits and monitoring thresholds to ensure they match between CC and MC configurations.

Incorrect velocity parameters can compromise machine safety

Test Velocity Monitoring Function

Perform controlled test of safe velocity monitoring by commanding reduced speed operation and verifying both controllers recognize the safe state consistently.

Document velocity response times to identify timing mismatches