APPARATUS FOR READING A DISK-SHAPED RECORD CARRIER

摘要

23,10.78 1 PHN 9204 "Apparatus for reading a disk-shaped record carrier." An apparatus for reading a disk-shaped record carrier, the radial scanning position being controlled with the aid of a first servo control loop, which controls a positioning member for the read element depending on a control signal which is read from the record carrier. If this control is disturbed a second servo control loop is rendered operative. This second servo control loop comprises a position indicator for supplying a position signal which is representative of the radial position of the positioning member, a memory circuit for storing the value of this position signal at the instant of failure of the first servo control loop, and a differential amplifier for applying a control signal to the positioning member, which signal corresponds to the difference between the instantaneous and the stored value of said position signal. Furthermore, there is provided a control circuit for changing-over between the first and the second servo control loop and vice versa depending on a built-in criterion.