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Power off the machine and manually check axis movement. Disconnect the motor from the ballscrew (remove coupling) and rotate the ballscrew by hand to detect binding, roughness, or abnormal resistance. Check way covers for debris or collision damage.

Lockout/tagout required. Verify all stored energy is released before disconnecting coupling.

Check DIAGNOSIS screen > Servo > Position Deviation (D-number varies by series: typically #300-#307 for each axis). Note the deviation value when alarm occurred. Compare to Parameter 1826 (In-Position Check Width) - deviation exceeded this value.

Inspect ballscrew bearings, ballnut, and coupling for wear or damage. Check gibs and way lubrication. Verify lubrication system is functioning (check DIAGNOSIS > PMC for lube-related signals). Address any mechanical issues found.

After mechanical repair, perform a controlled jog test at low feedrate (10% rapid override). Monitor position deviation on DIAGNOSIS screen during movement and at stop. Deviation should settle to near zero within in-position tolerance.

Access SYSTEM > PARAM and verify Parameter 1825 (Position Loop Gain) for the affected axis. Typical values range 20-60 depending on machine rigidity. Compare to sister axes or OEM documentation. Check Parameter 2020 (Velocity Loop Gain), typical range 100-400.

Record all current parameter values before making changes. Incorrect gains can cause oscillation or runaway.

Verify Parameter 1826 (In-Position Check Width) is appropriate for the machine (typically 50-500 detection units, equals encoder pulses × Parameter 1821 ratio). If recently changed to a tighter tolerance, this may be unrealistic for the mechanical system.

Check servo amplifier LED status during alarm condition. Green LED solid indicates normal ready state. If LED shows red or flashing pattern, note code and reference amplifier manual (α/β series specific). Verify servo parameters match motor model using Parameter 2000-series motor specifications.

If gains are suspect, perform Auto-Tuning if available (MAINTENANCE > Servo Tuning menu on 30i/31i/32i series) or incrementally increase Parameter 1825 by 10% and test. Monitor for oscillation or hunting. Restore OEM parameters from backup if available.

Excessive gain causes audible oscillation and potential mechanical damage. Increase gains gradually with immediate E-stop access.

Check DIAGNOSIS > Servo > Current Position (absolute pulse values) and observe for erratic counting when axis is mechanically stopped. Compare encoder output on DIAGNOSIS screen with machine position display for discrepancies indicating feedback issues.

Inspect encoder cable routing for proximity to power cables, spindle cables, or inverters causing EMI. Check cable shield grounding at amplifier end only (not both ends). Verify encoder cable connector engagement at both motor and amplifier, check pins for corrosion or damage.

Never disconnect encoder cable with servo power ON - this will trigger immediate alarms and may corrupt absolute position data.

Access MAINTENANCE > Encoder Test (if available on 30i+ series) or monitor DIAGNOSIS > #0300-#0307 for position deviation noise. Stable deviation within ±5 counts is normal; erratic jumping indicates encoder/cable problems. Check encoder battery voltage if using absolute encoder (DIAGNOSIS > Battery, >20VDC required).