| 摘要 |
PURPOSE:To prevent malfunction by using an output of a count circuit so as to prevent malfunction of channel selection at antenna input selection and using an output of the counter circuit so as to control the display of the screen at the selection of external video input thereby making the threshold value of the counter circuit different depending on the selection of antenna input an external video input. CONSTITUTION:A horizontal synchronizing signal detected by a synchronizing signal detection circuit 16 is fed to a microcomputer 10, where the horizontal synchronizing signal per a prescribed time is counted. When the video signal of the number within a prescribed range is detected, it is discriminated that a video signal is inputted, and when not detected, it is discriminated that no video signal is inputted. Based on the result of discrimination, the AFT control is applied at channel selection to discriminate the invasion of an audio signal or noise and to control the display of the screen. The criterion differs from the channel selection and the screen display. Thus, malfunction at channel selection is surely prevented.
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