SV0435 Inverter: DC Link Undervoltage fault in Fanuc drive

SV0435 Inverter: DC Link Undervoltage fault in Fanuc drive

Description

SV0435 is a DC Link low voltage alarm detected by the Servo Amplifier (Inverter), not the PSM. While the PSM supplies the DC voltage, the Servo Amp measures it at its own input terminals. If the PSM says "Voltage is fine" (No SV0433) but the Servo Amp says "Voltage is low" (SV0435), it indicates a connection break between the two units.

Cause

• DC Link Bar Failure: The copper bus bars or jumper wires connecting the PSM to the Servo Amp are loose or missing.
• Blown Fuse on Drive: Some older drives have a DC input fuse.
• Sensing Circuit Failure: The voltage divider circuit inside the servo drive that measures the 300V/600V bus has failed, reporting 0V even when 300V is present.

Solution

1. Visual Inspection: Look at the top of the drives. Are the bus bars installed? Are the screws tight? A loose screw can arc and cause this alarm.
2. Measure Voltage: Carefully measure the DC voltage at the screws of the servo amp. If you measure 300VDC but the alarm is on, the drive's internal sensing circuit is broken (Replace Drive).
3. Check Adjacent Drives: If multiple drives show SV0435, the issue is likely at the connection point coming out of the PSM.