Came to fix can indeed be translated in est venu réparer, but also as est venu pour réparer. Both are correct, making your two first sentences correct. You can either use the one or the other to translate your original sentence.
The last sentence isn’t correctly built though. Adding à wouldn’t make any sense and would make your sentence incorrect. Pour is working because it is there to present a goal. In this sentence, the goal for the technician is to fix the light, so he came for that, pour ça.
So if we take another example, such as:
The woman came to buy some bread.
You could translate it as:
La femme est venue acheter du pain.
La femme est venu pour acheter du pain.
Leave a comment