Cassette auto changer system

A cassette auto changer system including a member for selectably providing a plurality of cassettes to be loaded into one or more tape signal readers. A cassette rack is provided including a plurality of cassette receiving compartments, a cassette port accessible from an outer side of the auto changer apparatus whereby cassettes may be inserted or removed from the auto changer apparatus, a tape transfer mechanism operable to selectably transport cassettes between the cassette rack and the tape signal reader, and the cassette port. A YES/NO sensor at the cassette port determines whether a cassette is present in the cassette port. In applicants' cassette auto changer system, when a YES indicator determined by the YES/NO sensor changes to a NO determination, a controller sets the cassette port an IN port empty condition. When in such IN port empty condition the YES/NO sensor changes to a YES condition to indicate the presence of a cassette in the cassette port, operation of the tape transfer mechanism to the cassette port is disabled and an IN port loaded condition is determined. When, in an IN port empty condition of the cassette port and operation of the tape transfer mechanism is detected by the YES/NO sensor, the controller determines an OUT port loaded condition of the cassette port. When in the OUT port loaded condition, a change from a YES indication to a NO indication is determined by the the YES/NO sensor, an IN port empty condition of the cassette port is determined by the controller.