SV0007

Navigate to DIAGNOSIS > PARAMETER and check parameter 1828 (position error detection level while stopped). Note the threshold value (typically 100-500 detection units).

Check DIAGNOSIS > SERVO > axis selection and monitor current position error (DGN300). If value fluctuates or grows while stopped, mechanical drift is occurring.

For vertical axes, manually verify brake operation: Servo OFF the axis and confirm mechanical brake engages (axis should not fall). If axis drifts, inspect brake pad wear, air pressure (pneumatic brakes), or brake release voltage at amplifier connector CN1.

Ensure axis is safely supported before disabling servo to prevent crashes on vertical axes

Adjust parameter 2002#1 (brake sequence timing) if brake releases too early or engages too late. Verify brake confirmation signal DI via DIAGNOSIS > PMC > DI/DO screen matches actual brake status.

Check servo amplifier LED status codes. Solid red or flashing codes (consult amplifier manual for αi, βi, or αSV series) indicate feedback or communication errors. Record LED pattern for cross-reference.

Navigate to DIAGNOSIS > SERVO and check DGN310-313 (encoder feedback pulse count) and DGN300 (position error). If DGN310-313 values change erratically while axis is physically stopped, encoder is faulty.

Inspect encoder cable routing for damage, proximity to power cables causing EMI, or loose connectors at motor (JE) and amplifier (JD) ends. Measure encoder cable resistance and shield continuity per Fanuc specifications (<1Ω per conductor).

For absolute encoders, check battery voltage at amplifier (should be >3.0VDC for lithium cells). Replace encoder battery and clear alarm with parameter 1815#4 (absolute position lost detection) set to 0 temporarily during re-establishment.

Record current absolute position before battery replacement to avoid position reference loss

Access SYSTEM > PARAM > SERVO and verify parameter 1825 (position loop gain) is within recommended range for axis inertia ratio. Typical values 3000-6000 (0.1 msec units). Increase incrementally by 10% if too low.

Excessive gain increases can cause oscillation or hunting; test with short jog moves after each adjustment

Check parameter 2021 (velocity loop gain 1st) and 2022 (velocity loop gain 2nd). Compare to factory recommended settings based on motor model and load inertia ratio (available in servo motor specification manual).

Monitor DIAGNOSIS > SERVO DGN020 (current command) while axis is stopped. Non-zero fluctuating values indicate amplifier drift. Perform amplifier offset adjustment procedure per Fanuc maintenance manual (typically accessed via DGN890-899).

If drift persists after gain adjustment and offset calibration, swap amplifier with known good unit of same model. Clear alarm history and test. If alarm moves to new axis, amplifier is defective; if alarm remains, revisit mechanical or feedback causes.

Ensure parameter backup before amplifier replacement; axis-specific servo parameters may require restoration