SV0426 Disconnect Alarm (Separate Detector) fault in Fanuc drive

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SV0426 Disconnect Alarm (Separate Detector) fault in Fanuc drive

Description

SV0426 is the specific "Disconnect" alarm for systems using a Separate Detector (External Scale) interface unit. It differs from SV0447 (which is a general hard disconnect) by pointing specifically to the 5V power supply or differential signal loss at the interface card level. It implies the interface unit sees the scale, but the signals are flatlining.

Cause

  • Unplugged Scale: The scale connector is loose.
  • Broken Wire: The 5V supply wire in the scale cable is broken.
  • Interface Card: The separate detector interface card (on the CNC or Drive) has a blown fuse for the scale power.

Solution

  1. Check LEDs: Look at the Scale Interface Unit (if equipped). Is the "Power" LED on? If not, check the fuse on the unit.
  2. Measure Voltage: Check for 5V at the scale end.
  3. Bypass: Set parameter 1815.1 (OPT) to 0 to disable the scale and run on motor encoder to verify the motor is fine.

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