SV0446 Hard Disconnect (Built-in) fault in Fanuc drive

SV0446 Hard Disconnect (Built-in) fault in Fanuc drive

Description

SV0446 is the "Hard Disconnect" alarm specifically for the motor's built-in Pulsecoder. While SV0445 is a "Soft" (data) disconnect and SV0447 is for "External" scales, SV0446 means the servo amplifier has detected a physical voltage fault on the feedback line from the motor. The drive monitors the +5V and 0V lines, as well as the differential pairs. If the voltage feedback is completely absent (open circuit), SV0446 triggers instantly to prevent the motor from running away without feedback.

Cause

• Unplugged Cable: The most obvious cause is the cannon plug at the motor or the connector on the drive (JF1) being disconnected.
• Broken Wire (Power): The specific wires carrying the +5V supply to the encoder are broken inside the cable track.
• Blown Fuse: The servo amplifier has an internal fuse protecting the 5V encoder supply rail. If this fuse blows due to a short, the encoder loses power.

Solution

1. Check Connections: Inspect the motor connector. Is it screwed on tight? Check the JF1/JF2 plug on the drive.
2. Measure Voltage: At the motor end, measure between the +5V and 0V pins. If you read 0V, unplug the cable at the drive and measure the drive output pins.
   • If the drive has 5V but the motor end has 0V, the cable is broken.
   • If the drive has 0V output, the drive's internal fuse or regulator is blown (Replace Drive).
3. Wiggle Test: If intermittent, run the machine while manipulating the cable in the drag chain.