438

Power down the CNC and disconnect motor power cables (U, V, W) at the amplifier end. Use a megohm meter (megger) to test insulation resistance between each motor winding phase (U-V, V-W, W-U) and between each phase to motor ground/frame. Acceptable resistance should be >10 megohms at 500VDC test voltage.

Discharge motor windings and wait 5 minutes after power-down before megger testing. High voltage testing can damage electronics if not properly isolated.

Measure winding resistance with a precision ohmmeter between U-V, V-W, and W-U. Compare values to motor nameplate specifications. Resistance values should be balanced within 5%. Significant deviation or near-zero resistance indicates winding short circuit.

Inspect motor power cable routing for pinch points, cable carrier damage, or sharp edges that may have damaged insulation. Check cableentry points at motor and amplifier for chafing or conductor exposure.

If motor tests faulty, replace motor and verify amplifier functionality using diagnostic screen SYSTEM > DIAGNOSIS > SERVO (parameter screen depends on control series: 0i/16i use #300-#399, 30i/31i/32i use #400-#499 range) to monitor current load values during manual jog before returning to automatic operation.

Power down and visually inspect the entire motor power cable run from amplifier to motor. Pay special attention to cable carrier entry/exit points, areas with tight bend radius, and any signs of cable jacket wear or crushing.

Disconnect motor power cables at both amplifier (TB1 or CN1 depending on amplifier type) and motor ends. Perform continuity test on each conductor and verify no short circuits exist between U-V, V-W, W-U phases or between any phase and shield/ground.

Tag and photograph cable connections before disconnection to ensure proper phase sequence on reconnection. Incorrect phase connection can cause alarm or motor rotation issues.

Inspect connector pins at both ends for bent pins, corrosion, or carbon tracking. Check for proper connector seating and locking mechanism engagement. Verify cable shield/drain wire is properly terminated only at amplifier end.

If cable damage is found, replace entire motor power cable with Fanuc-specified cable type. After replacement, verify proper operation by monitoring DIAGNOSIS screen #400 (alpha/beta SVU current feedback) or parameter #300 (16i/18i current monitor) during slow axis movement before resuming production.

After confirming motor and cable integrity, check amplifier LED diagnostic codes. Alpha/Beta series SVU amplifiers display 7-segment LED codes: observe for codes indicating IPM fault (typically flashing patterns). Refer to amplifier label or manual DESC.002E for specific LED code interpretation for your amplifier model.

Check servo alarm history in SYSTEM > ALARM > HISTORY to identify if alarm 438 occurred immediately at power-on or only during motion. Immediate occurrence suggests amplifier fault; occurrence during motion suggests motor/cable issues. Also check for preceding alarms (414, 415, 437) indicating thermal or other inverter warnings.

Temporarily swap the suspect amplifier channel with a known-good axis amplifier (if multi-axis amplifier) or swap entire amplifier module. Update axis control parameters (parameter #1020 for axis number assignment, #1825-#1832 for amplifier channel assignment on 30i/31i series) to match new configuration. Test if alarm follows amplifier or remains with motor.

Backup all parameters before modification. Incorrect servo parameter settings can cause dangerous machine movement or additional equipment damage.