SV0427 Soft Disconnect (Separate Detector) fault in Fanuc drive

SV0427 Soft Disconnect (Separate Detector) fault in Fanuc drive

Description

SV0427 is the "Soft Disconnect" alarm for external linear scales, analogous to SV0445 for motors. It indicates that the position data from the scale changed abruptly or the amplitude of the analog sine wave (A/B signals) fluctuated momentarily, but did not completely disappear. It is often a precursor to a hard failure or a sign of intermittent connection issues.

Cause

• Dirty Scale: A smudge of oil on the glass scale causes the signal amplitude to drop momentarily as the reader head passes over it.
• Vibration: Heavy machining causes the reader head to "bounce" relative to the scale body.
• Cable Flex: Intermittent wire contact in the cable track.

Solution

1. Clean Scale: This is the most common fix. Clean the scale glass carefully.
2. Check Cable Routing: Ensure the scale cable is not pulled tight during axis movement.
3. Disable Scale: To verify, disable the scale (Param 1815 Bit 1). If the machine runs fine, the issue is strictly in the scale system.