| 摘要 |
<p>PURPOSE:To prevent disturbance of the drum servo system, by providing the first and the second detecting circuits which detect drop-out of the reproducing horizontal synchronizing signal and noise in the video signal and by holding the drum rotation frequency voltage, by which the frequency of the horizontal synchronizing signal is caused to approach a prescribed value, when outputs of these detecting circuit are obtained. CONSTITUTION:Horizontal synchronizing signal PBH is supplied to reproducing period detecting circuit 6, horizontal synchronizing signal drop-out detecting circuit 18, and noise mask circuit 22 through gate circuits 15 and 16. Pulse width modulation signal PWM is formed according to the reproducing synchronizing signal by circuit 6, and servo voltage C is output by LPF7. The output detected by circuit 18 is applied to circuit 16 and gate 19 to generate artificial modulation signal PWM at the output of circuit 1. Output Q of circuit 22 is applied to counter 23 and is counted, and the output is applied to gate 20. When horizontal synchronizing signal drop-out and noise are detected by circuits 18 and 22, modulation signal output from circuit 6 is held in FF21 and is output from output circuit 17, thereby preventing disturbance of the servo system.</p> |
