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Common Causes

• BL motor encoder producing wrong speed feedback
• VAC motor resolver or magnetic encoder, or its cable/connector, faulty
• Encoder-link cable/connector intermittent or picking up noise
• Inverter unit control board speed-loop or feedback interface failure

Troubleshooting Steps

1. 1Read the code number shown with the alarm: code displayed value = Motor speed measured at the trip point; the manual defines it as rev/4294967296 divided by the speed-control frequency Tv.
2. 2Record the object and the displayed speed code, then determine whether the motor truly oversped: listen for abnormal acceleration, check the last commanded move/spindle command, load condition and any recent tuning or drive work.
3. 3Stop the machine and isolate power with DC-bus discharge before opening cabinets; identify the feedback type for that motor: BL motor encoder, or VAC resolver/magnetic encoder with separate feedback cable.
4. 4Inspect and reseat the feedback connectors at motor and inverter ends; check for oil contamination, loose pins, chafed cable, missing shield clamp and routing parallel to high-current motor leads.
5. 5If safe and repeatable, compare the feedback device or cable with a known-good identical axis/spindle channel to see whether the alarm follows the feedback hardware or stays on the drive channel.
6. 6If feedback hardware is clean but the motor still accelerates beyond command, treat it as a drive/control-board hazard and keep the machine out of service until the inverter unit control board is checked.