Abstract: An apparatus has a part which can be moved to an operating position by an actuating device, in response to movement of a button to an on position. Upon movement of the part to its operating position, a latching member directly associated with the part latches the button in its on position. Upon sensing a predetermined condition in the apparatus, a control member prevents the transmission of the actuating movement by the actuating device to the part, and a user becomes aware that the part has not moved to its operating position because the button does not become latched in its on position.

Abstract: A magnetic-tape apparatus (1) comprises at least two buttons (9, 10, 11) for selecting modes of operation of the apparatus and at least one apparatus part (37) to be positioned in conformity with the modes selected by actuation of the button. For positioning the apparatus part (37) the apparatus comprises a servo mechanism (50) which can be driven by a motor (27), which mechanism comprises a first eccentric means (71) arranged on a servo wheel (52), a drive member (73) which is movable by this eccentric means (71), and an actuating member (85) which is movable by the drive member (73) for positioning the apparatus part (37).