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ErrorLib — Industrial Fault Code Library

Disclaimer: ErrorLib is an independent technical reference tool. While we aim for accuracy, always verify with the manufacturer’s official service manuals before performing maintenance on industrial equipment. ErrorLib is not affiliated with the brands listed.

U

Energy Supply Stop (ECM)

Fanuc · Alpha i Series AC Servo Motor and Spindle

What does U mean?

A potential difference across a capacitor module is more than 300V, indicating an energy supply issue or abnormal voltage condition.

Common Causes

  • Charging current exceeds the allowed limit.
  • Faulty charging circuit or power supply.
  • Capacitor bank is not charging efficiently.
  • Overcharging the capacitor module.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Measure the voltage across the capacitor modules to confirm it exceeds 300V.

  2. 2

    Check the input power supply to the ECM for stable operation.

  3. 3

    Verify the internal charging and discharge circuits of the ECM for proper voltage regulation.

Browse all codes in this manual (29)
Verified technical data. Last updated: April 2026

Related Faults

08Regeneration Excess Alarm1Over-current at Power Running (ECM)2Over-current at Regeneration (ECM)
Source: Fanuc Alpha i Series AC Servo Motor and Spindle
Open Manual (Page 588)Search more codes in this manual