button for ejecting the card 4 the element 29 is slidebly mounted through the front wall of the dashboard 2 and protrudes outwardly from the same in order to be accessible before introducing the tuner control unit 4 into its housing 5 the heel forming part 26 is in the awaiting position shown in dotted lines when the unit 4 is introduced into housing 5 the rear end of the same rests against the stop forming part 26a so as to tilt the heel forming part 26 clockwise in cavity 5b about its axis x x 39 until the plane face 26b1 of part 26b rests on plate 4 maintaining the latter correctly in position and ensuring perfectly the capacitive and electromagnetic couplings the fixing point of the spring to the extreme face of the stop forming part 26a move on an approximately circular trajectory from the position shown in dotted lines to the position shown in continuous line the heel forming part 26 is blocked in active position by the semi cylindrical part 26a abutting against the rear extreme face of unit 4 and also by the lever arm 26 the spring 27 having a very weak return force the user who wants to recover the tuner control unit 4 presses the push element 29 towards the left with respect to fig8 so as to pivote the lever arm 28 in a direction corresponding to the tilting of the heel forming part 26 towards its awaiting position in dotted lines during this tilting of the heel forming part 26 the semi cylindrical part 26a pushes back the unit 4 towards the right in the direction of arrow f2 in order to partly eject it from its housing 5 advantageously a stroke end contact not.