When troubleshooting a PLC, which of the following should be checked first?

Checking the power supply first when troubleshooting a Programmable Logic Controller (PLC) is essential because the power supply is fundamental to the operation of the PLC itself. If the power supply is not functioning correctly, the PLC will not operate, and all other functions will be irrelevant. A lack of power can also affect the communication across the network and with connected devices, making it impossible to diagnose further issues effectively. Ensuring that the PLC is receiving the correct voltage and is powered adequately can prevent unnecessary troubleshooting steps that may arise from assuming the system is simply malfunctioning.

Once the power supply is verified as operational, attention can be turned to other components like physical connections, software settings, and output devices. Each of these elements can introduce their own set of problems, but they all depend on the controller being powered correctly. Thus, checking the power supply first offers a logical and efficient starting point for troubleshooting.