SV0445 Soft Disconnect Alarm fault in Fanuc drive

SV0445 Soft Disconnect Alarm fault in Fanuc drive

Description

SV0445 is a "Soft Disconnect." Unlike a "Hard Disconnect" (which detects a physical break in the wire via voltage levels), a Soft Disconnect is a software-detected anomaly. The digital servo software monitors the position data coming from the Pulsecoder. If the data packet is received but the values jump impossibly far in a single millisecond (e.g., the axis "teleported" 10mm), the software concludes that the encoder feedback is intermittent or corrupted, rather than the axis actually moving that fast.

Cause

This is the classic "bad cable in the drag chain" alarm.

• Intermittent Cable Break: As the cable flexes in the track, the copper strands inside make and break contact momentarily. This doesn't trip the voltage alarm (Hard Disconnect) but scrambles the position data bits.
• Connector Pin Fretting: Vibration causes the pins in the cannon plug to wear, creating micro-gaps that interrupt the digital serial stream.
• Noise/Shielding: High-frequency noise from a VFD or plasma cutter induces spikes in the feedback cable that look like massive position jumps to the computer.

Solution

Troubleshooting requires physically manipulating the cables.

1. Wiggle Test: With the machine powered on (but servo off if possible to avoid runaways), violently shake and bend the feedback cable, especially where it enters the motor and where it bends in the cable track. If the alarm trips while shaking, you found the break.
2. Check Grounding: Ensure the shield of the feedback cable is grounded at the drive end. If it is grounded at both ends, you may have a "ground loop" introducing noise.
3. Replace Cable: If the alarm is intermittent and clears with a reset, it is almost certainly the cable. Do not replace the motor or drive until you have replaced the cable.