SV0364 Soft Phase Alarm (Pulse Coder) fault in Fanuc drive

SV0364 Soft Phase Alarm (Pulse Coder) fault in Fanuc drive

Description

SV0364 is a "Soft Phase Alarm" related to the digital communication between the built-in Pulsecoder (encoder) and the servo amplifier. Fanuc uses serial encoders. This alarm specifically usually points to an issue with the absolute position data integrity. It often appears alongside battery alarms or communication errors. It means the drive has detected corrupted data regarding the phase angle or position from the encoder but hasn't lost communication entirely.

Cause

The causes are typically related to signal integrity or voltage levels at the encoder.

• Weak Batteries: If the APC (Absolute Pulse Coder) batteries (usually 6V alkaline or lithium) are dying, the encoder signal voltage drops, leading to data packet corruption.
• Noise Interference: Electrical noise from the spindle motor or other high-voltage equipment inducing currents in the encoder cable shield.
• Dirty Connector: Coolant or oil inside the feedback connector increases resistance and degrades the digital signal.
• Vibration: Excessive vibration at the motor can cause momentary disconnection of the encoder reading head.

Solution

Dealing with Pulse Coder alarms requires care to avoid losing the machine's Home Position (Reference Return).

1. Replace Batteries: With the machine powered ON (to prevent losing home position), replace the backup batteries located on the amplifier or in a separate battery box.
2. Inspect Shielding: Ensure the feedback cable shield is clamped correctly to the ground plate in the cabinet. A floating shield acts as an antenna for noise.
3. Check Cable Routing: Ensure the encoder cable is not zip-tied directly to the high-voltage motor power cable. They should be separated to prevent induction.
4. Reseat Connectors: Power down, unplug the encoder cable at the drive and motor, clean, and reseat. If the alarm persists, the Pulse Coder unit on the motor may be failing and requires motor repair.