We have checked the driver's actuator and it is working. Power is reaching it too. Then the rear one on the driver's side. Everything great as well. The only difference between them is an sliding mechanism that have a contact wires to command the other doors (secondary and smaller set of wires).

Following the wires, we have found this under the dash. It's probably the remote central locking unit (key-less system).

Former owner have lost the main key with remote door opening. So we tried to fix some contacts that looked bad (reinforce the welds). Nothing. Then we fed power directly in there and got a response. But some on the actuators kind of of get jammed most of the times (to the point where you cannot even get it open manually with the key on the lock cylinder).
We have also noticed what seems to be an infrared frequency receptor on the driver's door, near to the lock cylinder. There is probably a switch in there and it could be the problem as we could find nothing else.
If anyone went through something similar, please help!!!
cheers