SV0437 Input Circuit Overcurrent fault in Fanuc drive

SV0437 Input Circuit Overcurrent fault in Fanuc drive

Description

SV0437 is distinct from the more common SV0438 (Inverter Overcurrent). While SV0438 deals with the output (motor side), SV0437 deals with the input side of the servo amplifier. It indicates that the current flowing from the main DC link into the specific servo inverter section is excessively high. This alarm is generated by the Power Supply Module (PSM) monitoring the input to the specific drive, or by the drive itself detecting a short across the DC rail input terminals.

Cause

• Internal Bus Short: The internal bus bars or capacitors inside the servo amplifier are shorted together.
• Transistor Latch-up: The IGBTs are failing in a way that allows DC current to flow continuously (shoot-through) without switching.
• MCC Timing: On some older systems, if the Magnetic Contactor (MCC) closes out of sync with the pre-charge cycle, the sudden inrush triggers this.

Solution

1. Disconnect DC Link: Power down and remove the copper bus bars connecting the drive to the PSM.
2. Resistance Check: Measure the resistance across the P (Positive) and N (Negative) terminals on the servo drive. It should charge up (capacitance) to high resistance. If it reads a dead short (0 Ohms), the input capacitor bank or IGBT module is destroyed.
3. Replace Amplifier: This is a catastrophic internal failure. The drive must be replaced.