To the original poster... and to those looking for a chunk of metal.. i.e. an actual component called the "Yaw Damper"... IT DOESN'T EXIST! (At least not on the A330, A340, B777 and all modern aircraft.)
As grounded27 mentioned, Yaw Damping on FBW aircraft is a software function of the of the PFCS. Using inertial references, the primary flight control computers calculate an opposing input and feed it to the rudder servos.
A330s and A340s have a BYDU (back-up yaw damper). If the PRIMs fail, hydraulic fluid (B&Y) enters the BYDU, drives a generator to supply electricity for a small computational unit and a set of gyros. Signal output then commands a hydraulic actuator inside the BYDU to give inputs to the rudder servos input system, thus driving the rudder to provide a yaw damping function.