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Power down the machine completely and verify lockout/tagout procedures are followed.

HIGH VOLTAGE - Ensure complete power isolation before inspecting connections

Inspect the U, V, W power cable connections at both the spindle drive output and motor terminal box for proper phase sequence per wiring diagram.

If recent work was performed, swap any two of the three power phases (U-V, V-W, or U-W) at either the motor or drive end to reverse rotation direction.

Only swap phases at one location, not both ends

Restore power and test spindle rotation in M03 and M04 modes at low speed (200-300 RPM) to verify correct directional response.

Access the spindle drive diagnostics screen and monitor encoder feedback signals (A, B, Z pulses) while manually rotating the spindle by hand in both directions.

Ensure spindle is in emergency stop mode before manual rotation

Check encoder cable connections at both motor and drive ends for security, pin damage, or corrosion. Verify cable shield is properly grounded at drive end only.

If encoder was recently serviced, verify A and B channel connections are not reversed. Check parameter 4020 (encoder type) and 4022 (pulses per revolution) match the installed encoder specifications.

If encoder signals are erratic or absent, replace the encoder cable first, then test. If alarm persists, the encoder itself may require replacement.

Compare current parameter 3741 setting with machine-specific parameter backup or manufacturer documentation. Default is typically 0, but some machines require 1 for reversed logic.

Record all parameter values before making changes

Check parameters 4002 (serial spindle channel), 4020-4024 (encoder settings), and 4132-4135 (orientation parameters) against OEM specifications for proper spindle configuration.

If parameters were recently changed or restored, reload verified backup parameters from a known-good configuration or contact machine manufacturer for correct parameter set.

After parameter correction, cycle power to the entire system, perform spindle reference position return if equipped with orientation, then test rotation in both M03 and M04.