PLC Fault Finding & Troubleshooting Procedures The following tables list some PLC Fault Finding common problems and troubleshooting procedures for the PLC systemin the event of faulty operation. PLC Fault Finding and Troubleshooting System Operation Symptom Troubleshooting and Corrective Actions for PLC system PLC Fault Finding & Troubleshooting Procedures Corrective Actions for PLC system All LEDs are OFF 1 . Check the power supply wiring. 2 . Check If the power supplied to the PLC control units is in the range of the rating. 3 . Be sure to check the fluctuation in the power supply. 4 . Disconnect the power supply wiring to the other devices if the powersupplied to the PLC control unit is shared with them.If the LEDs on the PLC control unit turn ON at this moment, the capacity of the power supply is not enough to control other devices as well. Prepare another power supply for other devices or increase the capacity of the power supply. 5 . ...