Measure the voltage across the input terminal and the common ( COM ) line. It must match the rated voltage (e.g., 24V DC). If voltage is present but the LED is off, the input optocoupler circuitry may be damaged.
Indicates a hardware error, memory corruption, or a watchdog timer timeout. A flashing red light often denotes a non-fatal program error, while a solid red light points to critical hardware failure. Common Diagnostic Error Codes and Solutions Symptom / LED State Potential Cause Troubleshooting Steps POWER LED is OFF No incoming power or blown fuse. idec plc fa2j manual