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ErrorLib — Industrial Fault Code Library

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AC-INPUT-NO-ON

AC Input Signal Not Turning ON

Mitsubishi Electric · MELSEC iQ-R I/O Module

What does AC-INPUT-NO-ON mean?

An AC input signal fails to turn on, typically caused by step-like deformations in the input signal waveform around the zero-cross voltage. This issue often arises from power supply quality problems, such as those associated with off-line type Uninterruptible Power Supplies (UPSs).

Common Causes

  • Deformed input signal waveform around the zero-cross voltage, preventing proper detection by the AC input module.
  • Use of an off-line type UPS or other power supply that generates insufficient or distorted AC waveforms.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Improve the input signal waveform by using an on-line type UPS or other power conditioning device that provides a cleaner, stable AC waveform.

Browse all codes in this manual (56)
Verified technical data. Last updated: April 2026

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Source: Mitsubishi Electric MELSEC iQ-R I/O Module
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