| 摘要 |
PURPOSE:To prevent unnatural disorder from occurring to an image by detecting whether the input signal of a tuner has a desired receive frequency or not from the output signal of a discriminator. CONSTITUTION:When a channel selection signal is inputted from an input device 9, a microcomputer 10 outputs data for supplying a voltage for channel selection to the tuner 1 to a D/A converter 8. The microcomputer 10 performs normal AFT operation with the frequency increase/decrease detection signal of an automatic fine tuning function AFT and completes channel selecting operation when a video signal processing circuit 5 obtains a normal synchronizing signal. When the increase/decrease detection signal of the AFT is not obtained, the tuning frequency of the tuner 1 is decreased by about 250kHz and search-up operation is started a specific time later to detect whether the output signal of the frequency discriminator of an intermediate frequency amplifying stage 4 increases or decreases. When the detection signal is obtained, the microcomputer 10 performs the normal AFT operation, and when not, the tuning frequency is further decreased to repeat the same operation as mentioned above. |
