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Power off the machine and visually inspect the encoder cable along its entire length, especially in the cable track. Look for kinks, cuts, or areas where the cable has been pinched or abraded.

Always power off before disconnecting encoder cables to prevent damage to encoder circuitry

Check encoder connector at the motor (typically JA7A or similar designation on αi/βi servo motors) and at the amplifier JD1A connector. Ensure connectors are fully seated and locking tabs are engaged. Check for bent pins or contamination.

Perform continuity and insulation resistance test on encoder cable using multimeter. Check shield continuity and verify no short circuits exist between signal lines. Replace cable if any faults detected.

Check servo amplifier LEDs. A-series amplifiers show specific patterns: red ALARM LED lit continuously indicates encoder error. Consult amplifier manual for LED diagnostic codes specific to your αi or βi series amplifier.

Access DIAGNOSIS screen > SYSTEM > PARAM > Set DGN parameter display. Check diagnosis number 300 (Encoder I/F diagnosis) for the affected axis to verify encoder communication status and error counters.

Measure encoder power supply voltage at the amplifier connector JD1A. Verify +5V is present and stable (±5% tolerance). Check diagnosis 310-319 for serial encoder communication errors if using αi series serial pulse coder.

Use caution when measuring voltage on live circuits - ensure proper meter probe contact to avoid short circuits

Check parameter 2020 (serial encoder type) and parameter 2022 (encoder output pulses) match the actual encoder installed on the motor. Mismatched settings cause communication failures.

Verify noise suppression. Check that encoder cable shield is properly grounded only at amplifier end. Ensure encoder cables are routed away from power cables and noise sources. Check parameter 1815 bit 0 (encoder noise filter) if noise is suspected.

With power off, manually rotate the motor shaft slowly and feel for rough spots or resistance in encoder bearing. Encoder should rotate smoothly without binding or grinding sensations.

Ensure axis brakes are released and machine is in a safe condition before manually rotating axes

If encoder is accessible, inspect for contamination, oil ingress, or moisture. Check encoder mounting bolts for proper torque. Verify encoder coupling to motor shaft is secure and not damaged.

Substitute with known good encoder of same type if available, or swap encoder cables with another working axis temporarily to isolate whether fault is in encoder or amplifier/cable. Observe if alarm follows the encoder or remains on same axis.

If encoder replacement is required, record position offset data from parameter 1815-1824 (position offset) before replacement. After encoder replacement, perform reference position return and verify position accuracy using diagnosis screens 50-53 (position deviation).