308

Check DIAGNOSIS screen > SERVO > APC BATTERY (path varies by series: 0i/16i use SYSTEM > DIAGNOSIS > #300-399, 30i/31i/32i use DIAGNOSIS > SERVO > APC). Record battery voltage values for the affected axis.

Identify the motor serial number and battery type for the affected axis. Replace the APC battery on the motor encoder with correct Fanuc part (BR-2/3A with connector for alpha/beta servo, A98L-0031-0025 for older models). Battery is typically located on motor rear cover.

Battery replacement must be completed within 15-30 minutes of disconnection to prevent loss of absolute position data. Do NOT power down the servo amplifier during replacement.

After battery replacement, clear alarm 308 using RESET key. Verify alarm does not return and check APC battery voltage on DIAGNOSIS screen shows >3.0V DC (normal range 3.2-3.6V).

If alarm persists after battery replacement, perform APC data reset via parameter PWE=1, then SYSTEM > PMC > SETTING > INITIALIZE APC (path varies by control). Re-establish reference position using return-to-zero procedure for the affected axis.

APC reset will erase absolute position data. Machine must be manually homed after this operation.

Power down the servo amplifier for the affected axis (if absolute position loss is acceptable) or prepare for hot-swap battery replacement. Remove motor rear cover to access APC battery connector.

If machine absolute position must be preserved, perform this inspection with amplifier powered and complete inspection within 15 minutes.

Inspect battery connector (CN on encoder board) for corrosion, oxidation, or damage. Check battery holder contacts and encoder PCB connector pins. Clean contacts with electronics cleaner if corrosion is present.

Disconnect and reconnect battery connector firmly ensuring proper seating. Measure battery voltage directly at battery terminals with multimeter (should read 3.2-3.6V for healthy battery). Compare to voltage reading on DIAGNOSIS screen.

If voltage at battery is normal but diagnosis screen shows low, suspect encoder PCB issue. Replace encoder battery assembly or entire encoder if connector damage is severe. Clear alarm and monitor for 24-48 hours.

Verify fresh battery voltage reads 3.2-3.6V on multimeter independent of encoder. Install known-good battery and observe if alarm 308 clears or persists. Check servo amplifier LED status (green steady is normal, red indicates encoder fault).

Check encoder cable (alpha series typically 4-core shielded) for damage, shield continuity, and proper grounding. Inspect cable at both motor and amplifier connectors (JD1A/JD1B on alpha drives). Verify connector pin integrity.

Do not disconnect encoder cable while servo power is ON. This will cause immediate loss of position data and potential SV0441 alarm.

Review servo alarm history via ALARM > HISTORY menu for related alarms (SV0441 encoder error, SV0310 APC error). Check parameter 1815#0 (absolute encoder selection) is set correctly for encoder type installed.

If alarm persists with new battery and good connections, encoder replacement is required. Order replacement encoder with same specification (serial encoder for alpha, pulse-coder for AC servo). After replacement, perform APC setup and machine zero return procedure.

Encoder replacement requires re-establishing machine reference position. Document current position offsets from parameters 1850-1854 before replacement.