416

Check DIAGNOSIS screen > [SYSTEM] > [SERVO] > Diagnostic 201 (or #201) for the affected axis. Look for status bits indicating cable disconnection or signal loss (typically shows as 0000 or abnormal values for pulse coder feedback).

Power OFF the CNC system. Inspect the pulse coder cable from motor to amplifier. Check connector security at both motor-side (typically M12 or M23 connector) and amplifier-side JD1A/JD1B connectors. Look for bent pins, corrosion, or cable shield damage.

Ensure power is OFF before disconnecting any pulse coder cables to prevent damage to encoder circuits.

Perform cable continuity test using a multimeter on all pulse coder signal lines (A+, A-, B+, B-, Z+, Z-, shield). Compare readings with Fanuc Connection Manual for your amplifier series (αi, βi, or αis). Replace cable if any open circuits detected.

Check servo amplifier LED display. A 'dC' (disconnection) or flashing alarm LED indicates loss of encoder feedback. After cable repair, clear alarms and perform a controlled axis movement test in JOG mode at low feedrate (F10-50).

Check DIAGNOSIS screen > Diagnostic 300 through 307 (axis 1-8 respectively) for current pulse coder feedback values. Manually rotate the motor shaft slowly and observe if position counts increment. No change indicates dead encoder.

Ensure machine is in EMERGENCY STOP before manually rotating motor shafts.

Measure pulse coder power supply at motor connector. Verify +5VDC ±5% (older systems) or +12VDC (newer αi systems) between power pins. Low voltage indicates amplifier power supply fault; correct voltage with no signals indicates encoder failure.

If available, temporarily swap the pulse coder cable with an adjacent working axis. If alarm follows the cable, cable is faulty. If alarm stays with original axis, pulse coder or amplifier channel is faulty.

Replace pulse coder and perform setup. Set Parameter 1815 (serial pulse coder type) or 1820 (pulse coder number of pulses) to match new encoder specifications. Execute CONTROLLED AXIS SETUP if using absolute pulse coder, then establish reference position.

After encoder replacement, Parameter 1815 must match encoder specifications or severe position errors will occur.

Access DIAGNOSIS screen > Diagnostic 206 for the affected axis to check servo alarm history. Look for preceding alarms like 410 (overload), 414 (overheat), or voltage-related faults that may indicate amplifier damage.

Check servo amplifier LED status. Continuous red LED with '416' or 'dC' display indicates feedback circuit fault. Verify no physical damage, capacitor bulging, or burning smell on the amplifier module PCB.

If pulse coder and cable test good, swap the entire servo amplifier module with a spare or adjacent axis module (ensure Parameter 1020-1023 axis assignment is updated). If alarm moves with amplifier, replace the amplifier module.

Swapping amplifier modules requires updating Parameter 1020-1023 (axis to amplifier assignment). Incorrect assignment will cause incorrect axis movement.

After amplifier replacement, verify Parameter 2020-2027 (motor serial number) and Parameter 2001-2008 (servo motor type) match the connected motor. Clear all alarms, power cycle, establish reference position, and perform servo tuning check via DIAGNOSIS 380-387 (load meter).