| 摘要 |
PURPOSE:To avoid mis-adjustment, by making a diode conductive with a constant voltage of a tuner at the UHF mode and preventing a current from a UHF AGC voltage set variable resistor to the tuner at this conducting state. CONSTITUTION:One end of a variable resistor R4 is grounded via a resistor R5 and connected to a cathode of a diode D2. A voltage BV obtained at the turner 4 is applied to the anode of the diode D2. The voltage is 12 Volt at the VHF mode and 0 volt at the UHF mode. Since the terminal 5 is 12 Volt at the VHF, a diode D1 is cut off. The VHF AGC voltage is set by adjusting a variable resistor R2. Since the terminal 5 is 0 Volt at the UHF, the diode D1 is conductive. The UHF AGC voltage is set by adjusting the variable resistor R4. In this case, since the diode D2 is cut off, no current flows from the variable resistor R4 to the tuner. |
