Faulty power-pcb on Siemens Logo PLC

[asdqwerty]

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

[SeanB]

Standard SMPS unit so the TOP232 likely has died, along with the 2 SMD capacitors on the board, and check the input side resistors and diodes for being open circuit.

To prevent it happening again get some inline mains filters on the power to the PLC units, it will help prolong the life of them a lot.

[asdqwerty]

ok. I'll take a closer look at that area !