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Check the spindle amplifier LED status indicators and verify battery voltage on the amplifier (should be above 3.0V DC).

Low battery voltage will cause immediate parameter loss upon power cycle.

Access spindle parameters and verify parameters 4020-4024 (motor data) and 4130-4135 (calibration data) contain non-zero values.

If parameters show zero or default values, restore from backup file or retrieve motor nameplate data and motor specification documents.

Never input estimated values - use only verified motor specification data.

Execute spindle calibration procedure using MANUAL OFFSET function in the spindle drive diagnostics screen, following exact procedure in amplifier manual.

Ensure motor is disconnected from spindle belt/coupling before running auto-tuning to prevent mechanical damage.

Enter spindle diagnostic screen and monitor encoder feedback signals (A, B, Z pulse) while manually rotating spindle. Check for dropouts, irregular counts, or missing Z-pulse.

Rotate spindle by hand only - do not attempt motorized rotation with alarm active.

Inspect encoder cable for damage, proper shielding continuity, and secure connections at both motor and amplifier ends. Check for oil contamination on encoder connector.

Measure encoder power supply voltage at the encoder connector (typically +5V DC). Verify voltage is within ±5% tolerance and stable.

If encoder signals are unstable or absent, replace encoder cable first, then re-test. If problem persists, encoder head replacement is required followed by full recalibration.

After encoder replacement, all spindle calibration data must be re-entered and calibration procedure repeated.

Power cycle the complete system and observe if alarm returns immediately during amplifier initialization or only when attempting spindle rotation.

Immediate alarm on power-up indicates memory/hardware fault rather than runtime calibration mismatch.

Access amplifier self-diagnostics and run internal memory test if available. Check for additional fault codes in amplifier history log.

Swap spindle amplifier with known-good unit if available, transferring all parameter settings via backup file. Test if alarm clears with replacement amplifier.

Document all parameter settings and calibration data before amplifier replacement.

If alarm persists with replacement amplifier and verified parameters, suspect motor encoder internal fault. If alarm clears, original amplifier requires repair or replacement.

Contact Fanuc service for amplifier repair authorization and return procedure.