366

Power off the machine and manually rotate the affected axis motor shaft while observing for unusual resistance, grinding, or clicking sounds from the encoder end of the motor.

Ensure all safety lockout/tagout procedures are followed before manual manipulation of axis motors.

Access DIAGNOSIS screen path: SYSTEM > DIAGNOSIS > SERVO and monitor diagnostic numbers D0300-D0303 (Position Deviation) for the affected axis while jogging slowly. Erratic or spiking deviation values confirm encoder feedback issues.

Remove the motor from the machine and disassemble the rear encoder housing cover. Inspect the encoder coupling (flexible disk or spring coupling) for cracks, set screw looseness, or axial displacement. Replace coupling if any degradation is visible.

Mark motor and encoder shaft alignment before disassembly to maintain encoder phasing during reassembly.

After reassembly, verify encoder installation by executing the reference position return (G28) and checking current position display matches expected machine coordinates. Perform Parameter 1815 (Position Deviation Excessive Error Detection) check to confirm stable operation.

With the motor removed, carefully open the encoder housing and inspect the encoder disk (glass scale or metal grating) for contamination, scoring, or cracks. Clean with isopropyl alcohol and lint-free cloth only if contamination is present.

Never touch the encoder disk surface with bare hands. Use powder-free gloves to prevent oil contamination.

Check the encoder LED indicator (if visible through inspection port) or measure LED current at encoder connector pins using the amplifier diagnostic function. Refer to servo amplifier manual for specific pin assignments (typically pins vary by αi/βi series amplifiers).

If contamination cannot be cleaned or internal encoder components show wear, replace the entire encoder assembly. After replacement, execute reference position reset using Parameter 1815 bit settings and re-establish reference position via G28.

Verify encoder signal quality via DIAGNOSIS screen D0060-D0063 (encoder A/B phase pulse monitor) while manually rotating motor shaft. Consistent square wave patterns confirm proper encoder function.

Inspect the motor cable along its entire length, especially at stress points (motor connection, drag chain entry/exit, amplifier connection). Check for visible insulation damage, tight bend radii below manufacturer minimum, or cable flattening.

Do not perform continuity testing on encoder signals with power applied to the amplifier. Disconnect motor cable from amplifier before testing.

Measure cable shield continuity and resistance from motor encoder housing to amplifier ground (should be <1 ohm). Check encoder signal wire resistance between motor connector and amplifier connector (typically <5 ohms per conductor for standard cable lengths).

Temporarily swap the suspect motor cable with a known-good cable of identical specification. Clear alarm 366 (RESET button), execute axis motion test, and monitor for alarm recurrence. If alarm does not return, replace the original cable.

Ensure replacement cable matches original Fanuc part number specifications for encoder signal type (serial/parallel), shielding requirements, and bend radius ratings.

After cable replacement, verify proper shield grounding at both amplifier and motor ends. Check Parameter 2020 (Serial Encoder Communication Error Detection) is enabled and monitor ALARM HISTORY (SYSTEM > ALARM > HISTORY) for any residual encoder-related alarms during 24-hour burn-in period.