SV0368 Serial Data Error (Built-In) fault in Fanuc drive

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SV0368 Serial Data Error (Built-In) fault in Fanuc drive

Description

SV0368 indicates a communication breakdown specifically regarding the "Built-in" Pulsecoder. Unlike the Soft Phase alarm (which is data corruption), this often implies that the serial data packet simply isn't arriving at the amplifier. The communication protocol between the motor and drive is high-speed serial. If the drive requests position data and receives silence or a malformed start bit, SV0368 is generated.

Cause

This is typically a physical connectivity issue or Pulse Coder hardware failure.

  • Feedback Cable Damage: The most common cause is a crushed or cut feedback cable. Because these cables carry low-voltage digital signals, even a slight crimp that damages the shielding or internal twisted pairs causes failure.
  • Connector Oxidation: Corrosion on the pins of the Honda or military-style connector at the drive or motor end.
  • JF1/JF2 Ports: On the drive unit, the ports where the feedback cables plug in can sometimes suffer from broken solder joints on the PCB due to cable tension.
  • Pulsecoder Failure: The electronics inside the encoder on the motor have failed.

Solution

Swap tactics are the best way to diagnose this:

  1. Visual Inspection: Follow the entire length of the cable. Look for pinch points, melted spots, or areas where the cable is pulled tight in the track.
  2. Swap Cables (If possible): If you have two identical axes (e.g., X and Y are both the same motor type), power down and swap the feedback cables at the drive end. If the alarm moves to the other axis, the fault is in the cable or motor. If the alarm stays on the original axis, the fault is in the drive control board.
  3. Check Shielding Ground: Ensure the cable shield is grounded only at the drive end (typically) to prevent ground loops.
  4. Ohm the Cable: Disconnect both ends and check continuity of every pin. Also, check for shorts between signal wires and the shield. If any continuity is intermittent while wiggling the cable, replace the cable.

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