Possibly a discharged capacitor?

Certainly possible that caps are degraded. I’ve rebuilt two or three ECUs that had erratic operation due to capacitors having reached the end of their life. Very easy job, especially with the single sided circuit boards, and no through-plated holes.

But mind the polarity! Replace type for type, and if they’re electrolytic, get the polarity right. It generally let’s you know if you’re wrong when you turn it on.

Dud caps (capacitors) due to age frequently look wrong. Bulged, a bit discoloured, split on top.