SV0434 Inverter: Control Undervoltage fault in Fanuc drive

SV0434 Inverter: Control Undervoltage fault in Fanuc drive

Description

SV0434 is similar to SV0432 but applies specifically to the Servo Amplifier's control board, not the Power Supply. The servo drive (Inverter) takes the 24VDC control power from the PSM (daisy-chained via the CXA2A/CXA2B connectors). If this voltage arriving at the servo amp is too low, the logic circuits cannot drive the IGBT gates reliably, and the system trips SV0434.

Cause

• Daisy Chain Voltage Drop: If you have 6 drives daisy-chained together, the resistance of the cables and connectors adds up. The last drive in the chain might receive only 18V instead of 24V.
• Bad Connector: The CXA2 connector is loose or has a pushed-back pin.
• Internal Fuse: The servo amplifier has an internal surface-mount fuse on the control input that may have blown.

Solution

1. Measure at the Drive: Unplug the control power connector (CXA2B) at the specific drive showing the alarm. Measure the voltage on the cable. It must be >22VDC.
2. Check Preceding Drives: If the voltage is low, move upstream to the previous drive. Often, the output connector of the previous drive is the culprit.
3. Inspect for Shorts: If the voltage pulls down only when plugged in, the drive itself has an internal short on its 24V rail and needs repair.