This page focusses on the what the possible reasons could be when the FX5 PLC does not automatically go into RUN mode – after startup.
For the most part – we will assume that no PLC errors are being detected.

The following Root cause possibilities can be looked at – in a process of elimination:

Possible Root Cause 1: The Run/Stop/Reset Switch is not on RUN


Possible Root Cause 2: PLC CPU set to stop when an error occurs

Possible Root Cause 3: One of the inputs of the PLC is selected as the RUN terminal. This input is off – at Startup This the PLC CPU is off;

Possible Root Cause 4: The PLC has an older program in its memory – which was overwritten. However, some settings are still applicable.

Additional Troubleshooting Strategy:

If none of the above root cause possibilities are applicable – then the answer might lie within the PLC special status bit. In particular;

After the PLC is turned back to run mode – check the following register values: SM203, SM204, SM206