| 摘要 |
PURPOSE:To realize a tracking controlling method which quickly restores a tracking disturbed condition caused when a magnetic head is chocked with foreign matters, by switching the output value of a delay means to a fixed value when omission of synchronizing signals is detected by a means which detects the presence of the synchronizing signals in information signals for a continuous period which is (n) times (n is an integer of 2 or more) longer than a fixed peried. CONSTITUTION:When foreign matters adhere to a magnetic head 2 and the reproduced output of the head 2 is extremely dropped, synchronizing signals cannot be extracted from a synchronizing separator circuit 15, since the output of a demodulator circuit 14 disappears. As a result, omission of signals is detected by an omission detecting circuit 16 and the input side of a switching circuit 17 is switched from a one-frame delaying circuit 8 to a DC generating circuit 18, and then, the loop of tracking control is disconnected. Therefore, the case where the output of the magnetic head 2 is extremely dropped and the state of obtained tracking error signals becomes worse and, as a result, a wrong tracking condition takes place, can be prevented. Moreover, the value of DC is transferred to the one-frame delaying circuit 8 from the DC generating circuit 18 at this moment. Therefore, the cause of the reproduced output drop is eliminated and a normal condition is restored. |
