Ive not had the door card off myself, but they are all much the same.
remove the door card, take a look on or around the locking mechanism and you'll see what looks like a small electric motor.
It will be obvious, as it will have wires running to it.
There are a few on Fleabay if you need to visualise it, search "Grande Punto Central"
I'd start by checking the connections.
In all likelihood, its going to have 3 wires.
One for earth, one for open another for closed.
Check continuity on the earth, check for voltage on open and then closed.
If none of this makes sense, then you'll need to find help.
Good Luck