SV0402 SV Ready OFF (Group Alarm) fault in Fanuc drive

SV0402 SV Ready OFF (Group Alarm) fault in Fanuc drive

Description

SV0402 is a "Parent" alarm. It rarely appears alone. It signifies that the CNC axis card has requested the servo drives to turn on, but none of them are ready. Unlike SV0401 (which might be a specific axis), SV0402 usually means the entire servo system failed to initialize. It is a "System Not Ready" state. You will almost always see another alarm (like SV0438, SV0434, etc.) accompanying it in the history or on the drive displays.

Cause

• Missing 24V Control Power: The drives have no logic power, so they cannot communicate "Ready" status.
• Emergency Stop: The E-Stop button is pressed, removing power from the MCC coil.
• Communication Break: The fiber optic cable between the CNC and the first drive is unplugged.
• Axis Card Failure: The motion controller card on the CNC motherboard is dead.

Solution

1. Ignore the 402: Look for the *other* alarm. If you see "SV0402" and "SV0438," troubleshoot the 438. The 402 is just a symptom.
2. Check Drives: Open the cabinet. Are the LED displays on the drives lit up? If they are blank, check the 24V power supply and fuses.
3. Check Optical Cable: Ensure the COP10A cable is plugged into the CNC axis card.