SV0381 Abnormal Phase (Separate Detector) fault in Fanuc drive

SV0381 Abnormal Phase (Separate Detector) fault in Fanuc drive

Description

SV0381 is a startup phase check for external linear scales. When the system powers on, it reads the immediate state of the A and B phase signals. If both signals are high or low in a way that suggests a broken wire or short circuit (e.g., A and /A are both High), SV0381 is triggered immediately. It differs from SV0384 (Running Phase Error) as this is a static electrical check.

Cause

• Wiring Short: The cable has been crushed, shorting the A+ wire to the A- wire.
• Unplugged: The connector is physically disconnected.
• Wrong Pinout: A new cable was made, but the soldering pinout does not match the Fanuc standard for that specific feedback card.

Solution

1. Ohm the Cable: Disconnect both ends. Check for shorts between A/B/Z pairs and power lines.
2. Check 5V: Ensure the scale is receiving power. Without 5V, the output drivers in the scale cannot pull the signal lines high, resulting in an "Abnormal Phase" state (all low).
3. Verify Pinout: Consult the "Connection Manual (Hardware)" for your specific CNC model to verify the pinout.