Karel,

Electrolytic capacitors are probably the shortest lived of all components in common use, so I'd always suspect those first.

I've never seen an A-143-2, but I've found a good image of one on schneidersladen.de, via a google image search.  I see what looks like four identical boards, with at least two electrolytic capacitors each. 

You might be able to spot the difference between the capacitors on the faulty board and the others, but not necessarily.  Sometimes you can see damage, but not always.

You could desolder them and measure their capacitance, but a lot of meters give false readings on faulty ones - they tend to show a higher value, when the ESR increases.  They are mostly quite cheap to replace, so it may be better to just try that first.

If there are any tantalum bead capacitors, those can be damaged by reverse voltage, but otherwise are more robust.

- Andy