4

PSM/PSMR Main Circuit DC Link Undervoltage

Fanuc · Series 30i CNC

What does 4 mean?

This alarm indicates that the DC voltage (DC link) in the main circuit of the Power Supply Module (PSM) or Power Supply Module with Regenerative (PSMR) has dropped below its operational threshold. An undervoltage condition on the DC link can lead to unstable operation or shutdown of connected drive modules.

Common Causes

  • A small power dip has occurred in the input power supply.
  • Low input power supply voltage, potentially outside specified limits.
  • The main circuit power supply may have been switched off with an emergency stop state released, indicating a sequence issue.

Repair Steps

  1. 1

    Check the input power supply for transient power dips or sustained low voltage conditions.

  2. 2

    Verify the input power supply specification and ensure the actual voltage meets requirements.

  3. 3

    Check the sequence logic related to the main circuit power supply and emergency stop conditions.

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Verified technical data. Last updated: March 2026