| 摘要 |
PURPOSE:To detect whether or not the polarity of magnetic field impressed on a disk is right by providing a means for prohibiting actions at the time of deleting and recording with an output from an abnormality detecting means. CONSTITUTION:When the magnetic field is impressed in an opposite polarity, or the magnetic field does not occur or only small magnetic field occurs because the wiring of a field coil is disconnected or short-circuited, an input level to a comparator 39 becomes small and an output from the comparator 39 becomes 'L'. Then a switch 41 is made to be OFF and a constant-current circuit 31 is held in a state in which the light emission by a light emission power is prohibited, namely, in a write protect state. At this time the output from an EX-OR circuit 42 becomes 'H' and the switch 44 becomes OFF through a delay element 43 so that the current supply to the field coil 15 is made to be stopped and the write protect state can be securely held. Thus, a malfunction such as executing the recording and deleting in the state having a polarity different from normal one, can be securely prevented.
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