| 摘要 |
PURPOSE:To prevent the channel selector of TV equipped with a tuning voltage sweeping circuit from malfunctioning by specifying the value of the tuning voltage to a certain value when any synchronizing signal is not detected after the completion of channel selection. CONSTITUTION:The channel number of a desired station is inputted b keyboard switch 9, which outputs a channel selection signal. As the channel selection signal is outputted, the tuning voltage is swept and when it is swept as many as prescribed, a stop signal is sent out to stop the sweeping of the tuning voltage. Then, pulse generating circuit 23 generates a pulse a certain time later. Since the output of synchronizing signal detecting circuit 24 is held at H when no broadcast wave arrives, the output of latch circuit 25 is held at H and the tuning voltage is reset and held at 0 V at any time, so that any broadcast wave will not be received. If a broadcast wave arrives after the channel selection, the output of circuit 24 is held at L, so that a prescribed station will be received without resetting the tuning voltage. |
