380

Check alarm history (ALARM > HISTORY) to confirm alarm 380 appears consistently on the same axis. Note which axis (n) is affected in the alarm message.

Access diagnostics screen (DIAGNOSIS > SERVO) and check position feedback status for the affected axis. Verify if position data is frozen or erratic, confirming encoder failure rather than cable issue.

Power down the system and inspect the external pulse coder (separate detector) physically for any visible damage, contamination on optical disk, or burnt marks. Check cable connections at both encoder and amplifier sides.

WARNING: Discharge servo amplifier capacitors and follow LOTO procedures. Do not attempt to disassemble the pulse coder as it is a sealed unit.

Replace the external pulse coder assembly with OEM Fanuc replacement. After installation, perform reference position return and verify encoder feedback via DIAGNOSIS > SERVO screen. Check parameters 1815 (serial encoder type) or 1820 (absolute encoder type) match new encoder specifications.

WARNING: Absolute encoders require battery backup verification and may need position data re-establishment using parameter 1815#4 (APC) after replacement.

Power down and visually inspect the entire encoder cable run from servo amplifier connector (JD8A/JD8B for serial, JD2A/JD2B for separate) to the external pulse coder. Look for pinch points, cuts, or mechanical damage.

WARNING: Ensure machine is powered off and locked out before cable inspection.

Check connector pins at both encoder and amplifier ends for corrosion, bent pins, or contamination. Measure DC voltage at encoder connector (typically +5VDC for LED power) using a multimeter while powered on to verify power supply integrity.

WARNING: Use proper ESD precautions when handling encoder connectors. Do not short power supply pins.

Swap encoder cable with known good cable of identical type and length if available. Clear alarm and perform test jog. If alarm 380 does not return, replace original cable permanently.

If cable replacement resolves issue temporarily but alarm returns, suspect encoder connector wear or contamination. Clean connectors with electrical contact cleaner and apply dielectric grease, or replace encoder if connector is integral to housing.

Swap the encoder cable from the affected axis to a known good axis amplifier channel (if multi-axis amplifier) or replace with spare amplifier module. If alarm follows the amplifier, the encoder interface circuit is faulty.

WARNING: Power down completely and wait 5 minutes for capacitor discharge before swapping amplifier connections. Verify parameter 1020 (axis number assignment) is updated if changing physical axis positions.

Check servo amplifier LED indicators. For α/β series amplifiers, observe the LED display codes on the front panel. Consult Fanuc servo amplifier manual for specific error codes related to encoder interface (typically LED code 8 or 9 indicates encoder issues).

Review parameter 2020 (encoder type selection) and 1815/1820 (serial/absolute encoder settings) to ensure correct encoder type is configured. Incorrect settings may cause false LED failure detection.

If amplifier fault is confirmed, replace the servo amplifier module. After replacement, verify parameters 2020-2084 (servo parameters) match original settings, perform encoder calibration if required, and establish reference position.

WARNING: Record all servo tuning parameters before amplifier replacement as some may reset to defaults.