Centralized Closing Failure C.XSARA II

Hello everyone, I have a Citroen Xsara II and the central lock fails, I have tried to change the control pile and synchronize it according to the car manual, and it keeps failing when you want both when you open and when closing, to see if someone can tell me where the remote control receptor is located to check it, or give me another clue to be able to repair it.
Greetings to all.