Get into Santos Joint (It's a deadzone btw so bring lots of filters), Find a keycard there (In a room with Admin before getting in), then go to either Wing A-B or C and into elevator to the underground, find then another keycard in underground 1 and another one before going into Underground 2, then find the admin keycard, then go to Error aka Underground 3, fight a boss then grab the master keycard. Then get a rescue saw, inside one of the room is going to be a box. The Chainbreaker is inside of it