| 摘要 |
PURPOSE:To detect the tuning state, by applying the output of an AC voltage generating circuit to a tuner to change the tuning voltage while disconnecting an AFC loop in the tuning detector used in a TV receiver and detecting and displaying the output of an AFC detecting circuit. CONSTITUTION:The voltage from a tuning voltage generating circuit 6 is applied to an electronic tuner 1, and the intermediate frequency signal is not only given to a video wave detecting circuit 3 but also inputted to an AFC wave detecting circuit 5, and the AFC signal is applied to the tuner 1 through a switch 13 to form an AFC loop. In case of tuning, when the switch 13 is opened and a switch 14 is closed to change the tuning voltage by a variable resistor 15, the AC voltage from an AC voltage generating circuit 8 is applied to an adding circuit 7, and oscillation is performed witha local oscillation frequency of several tens kHz-several hundred kHz. The AFC signal corresponding to this frequency is applied to window comparators 9a-9e, and one of light emitting diodes 12a-12e corresponding to the AFC voltage is lit; and when the light emitting didoe 12c is lit, an optimum tuning point is discriminated. |
