Structural unit for an electric actuator, particularly for a heating, ventilating and/or air-conditionning damper of a motor vehicle

A casing bottom part has a holding area and a positioning device (1) for a detachable holder for boards with different types of function in a precise position regarding a drive shaft. Types of boards vary according to availability, structure or form of resistance slide-ways (8) or of electrically conductive sliding surfaces (9) that detect the rotating angular position of a drive shaft or switch off a drive motor in a defined rotating angular position for the drive shaft.