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Identify Missing Signal

Press MOD key → Select 'Diagnose' → Choose 'CC' → Navigate to the affected axis. Observe which specific signal shown in %4 parameter is not active (typically 'Controller Enable', 'Drive Ready', or 'Power Stage On').

Write down the exact signal name from %4 - this tells you whether the problem is at drive level (Drive Ready) or controller level (Controller Enable).

Inspect X116 Connector

Power off machine. Check X116 connector at both the servo drive and CC/UEC module. Verify pins are not bent, connector is fully seated, and locking mechanism is engaged. Check for corrosion or contamination.

Disconnect all power sources and follow LOTO procedures before inspecting electrical connections.

Verify EnDat Cable Integrity

Inspect EnDat cable between motor feedback and drive for damage, especially at cable carriers and routing points. Check cable shield connection at both ends. Swap with known-good cable from functioning axis if available.

EnDat cable faults often cause intermittent enable signals. If alarm occurs randomly during motion, cable flex failure is likely.

Test Signal Continuity

Using multimeter or oscilloscope, measure continuity on the specific feedback signal pins identified in step 1. Reference CC/UEC wiring diagram for correct pin assignments on X116 connector.

For digital enable signals, you should see 24VDC when drive is ready. Absence indicates broken wire or failed drive output stage.

Check Drive Status LEDs

Observe LED indicators on the servo drive front panel. Red or flashing patterns indicate active faults. Consult drive manufacturer documentation (Rexroth, Siemens, Bosch, etc.) for LED fault codes specific to your drive model.

Many drives buffer multiple faults. Even if one clears, others may still block enable. Always check full fault history.

Access Drive Diagnostics via CC

From TNC, press MOD → Diagnose → CC → select axis → choose 'Drive Parameters' or 'Drive Status'. Look for active fault codes or error messages in drive's internal registers displayed through CC interface.

Common blocking faults: F7902 (overcurrent), F7905 (DC bus overvoltage), F8070 (motor feedback error). Address these before attempting re-enable.

Verify DC Bus Voltage

In CC diagnose screen, check 'DC Bus Voltage' parameter for the affected axis. Should be within drive's specified range (typically 540-600VDC for 400V systems). Out-of-range values prevent drive enable.

DC bus overvoltage can indicate regeneration problems. Do not repeatedly attempt enable with high bus voltage.

Check Motor Feedback Connection

Verify motor encoder/resolver feedback is valid by checking 'Position Value' in CC diagnose. Manually rotate motor shaft slightly - position should change smoothly. No change or erratic values indicate feedback failure blocking enable.

For EnDat encoders, check 'EnDat Status' parameter. Any value other than 'OK' will prevent drive enabling.

Reset Drive Faults

After correcting any detected faults, perform drive reset by pressing NC Stop on TNC, then Cycle Start, or use M4500/M4300 PLC markers to cycle enable. Monitor if drive transitions to ready state in CC diagnose.

If fault immediately returns after reset without motion attempt, issue is in stationary conditions (power, feedback, configuration) not dynamic conditions (load, tuning).