SV0385 Serial Data Error (Separate Detector) fault in Fanuc drive

SV0385 Serial Data Error (Separate Detector) fault in Fanuc drive

Description

SV0385 is the "External Scale" version of the Serial Data Error. It means the digital communication between the Linear Scale (or interface box) and the Fanuc Drive has failed. This applies to serial scales (like Mitutoyo AT-series or Fanuc's own serial scales). The drive requested position data, and the scale returned a communication error code or gibberish.

Cause

• Cable Length/Quality: Serial data at high speed is very sensitive to cable capacitance. Using a homemade cable instead of the Fanuc specification cable causes this.
• Interface Unit: If the scale uses an external "Interface Box" (ADB), that box may have lost power or failed.
• Scale Voltage: The 5V supply at the far end of the scale cable is dipping below 4.7V.

Solution

1. Check Power: Verify 5VDC at the scale connector. If low, check for corrosion or use a thicker gauge power wire.
2. Shielding: Ensure the cable shield is grounded. Disconnect the shield at the scale end to prevent ground loops (ground at drive end only).
3. Interface Box: If an ADB box is used, check its power LED. Cycle power to the box.