SV0366 Pulse Miss (Built-in) fault in Fanuc drive

SV0366 Pulse Miss (Built-in) fault in Fanuc drive

Description

SV0366 is a specific feedback error for the "Built-in" Pulsecoder (the one inside the red cap on the motor). "Pulse Miss" means the drive detected a loss of pulse data integrity but not necessarily a communication timeout. It often implies that the quadrature signals (A/B phases) or the absolute serial data check-sum failed momentarily. It is often associated with high-speed operations where the encoder cannot keep up with the data transmission rate due to degradation.

Cause

• Vibration: Excessive vibration at the motor shaft (bad bearings, unbalanced tool) shakes the encoder optics, causing the read head to miss lines on the grating.
• Encoder Degradation: The photo-diode inside the encoder is weakening, and the signal amplitude is on the borderline of being readable.
• Noise: Electrical noise on the cable shield interfering with the digital signal packets.

Solution

1. Check Vibration: Put your hand on the motor housing while it is running. If it is vibrating excessively, check the machine mechanics or motor bearings.
2. Swap Motors: SV0366 is almost always internal to the motor's encoder. Since you cannot easily replace just the encoder in the field (requires alignment), swapping the motor is the standard test.
3. Shielding: Ensure the ground clamps on the feedback cable are tight and clean.