304

Power down the machine and inspect the encoder cable (typically separate from power cable on αi series motors) on the affected axis. Check for physical damage, sharp bends, pinch points, or areas where shielding may be compromised near cable carriers or routing points.

Ensure EMERGENCY STOP is active and verify all power indicators are off before accessing cables.

Disconnect encoder connectors at both the motor (round Hirose/circular connector) and amplifier (CN2 on αi amplifiers, JA7 on older Digital AC servos). Inspect pins for corrosion, contamination, or bent contacts. Clean with electronic contact cleaner if needed.

Do not force connectors. Note orientation and pin alignment. Contamination from cutting fluid or coolant is common in machining environments.

Check cable shield continuity and grounding at the amplifier end using a multimeter. Shield should have low resistance to amplifier chassis ground. Re-secure cable clamps ensuring separation from power cables and high-current lines.

After reconnecting, navigate to DIAGNOSIS > SERVO screen and monitor parameter 300-303 (serial pulse coder data) while jogging the axis slowly. Values should increment/decrement smoothly without jumps or freezing, indicating clean communication.

Check DIAGNOSIS screen position 208 for battery voltage alarm status or low battery warning. On older systems, check ALARM history for preceding alarms 308 (APC battery low) or 309 (APC data lost).

If battery voltage is low (<2.7V on diagnosis), replace the encoder battery following proper procedure. For separate APC units, battery is typically on the detector. For αi motors with integral absolute encoder, battery is inside the motor connector housing.

Reference parameter 1815 (absolute position loss detection). Setting to 0 disables position loss alarm but does not fix underlying issue. Replace battery promptly to prevent position loss.

After battery replacement, perform absolute position establishment procedure: Set parameter 1815#0=1, move axis to reference position, execute G28 or manual reference point return, then write absolute position using SYSTEM > PMC > APC or parameter 1850 (axis-specific absolute position setting).

Machine must be properly referenced to known mechanical position before establishing absolute zero. Incorrect position data will cause positioning errors.

Swap the encoder cable from the affected axis with a known-good axis cable to isolate cable vs. encoder/amplifier fault. Clear alarms and test. If alarm follows the cable, replace cable. If alarm stays on same axis, proceed to component testing.

Check servo amplifier LED diagnostic codes. Refer to amplifier label or manual for LED patterns. αi series amplifiers show communication errors with specific red/orange LED patterns on the front panel. Record LED status for each power-up attempt.

If cable is confirmed good, temporarily swap the servo amplifier with another axis of the same type (verify matching amplifier model and capacity). If alarm moves to the new axis, amplifier serial communication circuit is faulty. If alarm remains, encoder is defective.

Ensure amplifier ratings match motor ratings. Verify parameter 2020-2023 (motor/amplifier codes) match after swapping. Incorrect pairing can damage components.

Replace defective component (encoder or amplifier). After encoder replacement, absolute position must be re-established using parameter 1850 or APC setting procedure. After amplifier replacement, verify all servo parameters 2000-2100 series match original settings.

Encoder replacement requires motor disassembly on most models. Maintain cleanliness and proper reassembly torque specifications to prevent contamination or mechanical runout.