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Power off the machine and visually inspect the encoder cable from the motor to the amplifier. Check for cable pinching, excessive bending near connectors, oil contamination, or physical damage along the entire cable routing path.

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

Disconnect the encoder cable at both the motor and amplifier ends. Inspect connector pins for bent contacts, corrosion, or contamination. Clean connectors with contact cleaner if needed and verify pins are straight and properly seated.

Check cable continuity using a multimeter on all encoder cable conductors (typically +5V, 0V, DATA+, DATA-, and shield). Verify resistance is less than 1 ohm for power lines and proper continuity on data lines. Replace cable if any open circuits or shorts are detected.

Reconnect cable with proper torque on locking connectors. Power up and observe amplifier LED status. Check DIAGNOSIS > SERVO > SERIAL screen to verify encoder communication is restored. If alarm persists, proceed to next cause.

With power on and alarm present, measure encoder power supply voltage at the amplifier encoder connector. Verify +5VDC is present between the +5V and 0V pins. Voltage should be 4.75V to 5.25V. Low or absent voltage indicates amplifier encoder power circuit failure.

Use caution when measuring voltage on live circuits - ensure proper DMM probe contact to avoid shorts

Check servo amplifier LED indicators. Refer to the amplifier manual for your specific series (α-series, β-series, αi-series). A red LED or specific blink pattern typically indicates encoder communication error. Record LED status for reference.

Navigate to DIAGNOSIS > SERVO screen and check diagnostic number D0300 (encoder data reception status) for the affected axis. A value of 0 indicates no encoder data received. Also check D0020 (serial encoder alarm code) for specific encoder fault codes.

If amplifier voltage is correct but alarm persists with a known-good cable, the encoder itself is likely failed. Replace the motor encoder assembly. After replacement, perform encoder offset adjustment using SYSTEM > PMC > SETTING > ENCODER OFFSET or parameter 1815 (absolute encoder setting) as required for your encoder type.

Absolute encoders require battery backup - verify battery voltage above 3.0V after encoder replacement

Navigate to SYSTEM > PARAM and verify parameter 1815 (serial encoder type setting) matches the actual encoder installed. Common values: 0=incremental, 1=absolute, 4=separate absolute. Incorrect setting will prevent communication. Cross-reference with motor nameplate encoder model.

Check parameter 2000 (serial spindle/servo setting) and parameter 8131 (encoder pulse count) match the motor specifications. Verify parameter 1820 (encoder output specification) is correctly set for your encoder type (typically 4 for serial encoders).

Changing encoder parameters incorrectly can cause loss of reference position - document original values before changes

Swap the servo amplifier with an identical known-good spare or with another axis amplifier (if same type) to isolate amplifier vs. motor/encoder fault. If alarm follows the amplifier, replace the amplifier. If alarm stays with the axis, encoder or cable is faulty.

Ensure amplifier swap is performed with power off and amplifier parameters are transferred or re-entered for proper axis operation