On a place with lot of inductive load, SON-lamps, there are used some Siemens LOGO PLC's.
They tend to fail. It seems like the powersupply is the problem. I suspect voltage spikes.
They consists of 2 pcb. One power and relay (in-out) pcb, and one display-cpu pcb.
What I often do, is buy a new one, taking the power pcb from the new and mix with the old display-cpu pcb. And then it all works again.
I guess it's one component that fails..
Maybe someone have a suggestion for which component to investigate..?
Attached is pictures with two models of the power-input-output-pcb