BAND SELECT
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3.Circuit signals processing
(1) MF amplifying circuit
Received by antanna and processed by the high frequency tuner, the television signals will be transmitted by the
tunner as 45.75MHZ signals to sound surface filter through C112 coupling after being amplified by V102, and
then the MF signals of trapped wave in sound carrier wave from sound surface filter F45U will be sent to pin 5
and 6 of LA76814. The MF demodulation circuit of this TV set is completed through PLL carrier wave
generator and outside pressure control oscillator (T101) in LA76814. The MF frequency is adjusted by T101
adjustment, and output of AFC is generated by a numerical control IF-PLL circuit, and read and sent to CPU by
I
2
C bus for correction of MF signals frequency deviation. The external capacitor of pin 3 decides the time
constant of AGC
，
and high frequency amplication AGC will be transmitted by I
2
C bus through pin 4 for control
of high frequency tuner gain.
(2) Sound signals processing
The secondary sound MF signals are input via pin 54 of LA76814, and then demodulated in PLL tuner through
lowpass and limit inside LA76814. After demodulation, the sound signals will be amplified through inside
lowpass and transmitted via pin1. Pin 2 is FM output, C121 is deaccentuation capacitor, pin 9 is FM detector’s
DC filter connector and C117 is filter capacitor. The external AUDIO signals are input via LA76814 pin 51,
controlled by CPU. A swith inside I2C bus control LA76814 can be used for options of internal and external
signals. The sound signals are transmitted via LA76814 pin 1 to LA4225A pin 1 via C601 coupling and
transmitted from its pin 4, after being amplified by LA4225A, to the speaker. The mute circuit 1 is comprised
of V601, V602 and other components for Power On and Off mute. Circuit 2 is comprised of CPU mute pin
V603 and other components.
(3) Line sync processing circut
The line oscillation circuit of the TV set is fully comprised of LA76814 internal integrated components. The
brightness signals containing compound sync signals are transmitted to the internal sync seperation circuit for
line and field sync pulse.
(4) Line output circuit
Standard line oscilation pulse is output via pin 27 to V431 for line drive. T431 is H (L) drive used to convert the
low current and high pressure pulse signals from line tube into low voltage and large current signals for line
export needs. V432 is line output, C435 and C436 are reciprocal capacitor, C441 is S calibration capacitor,
L441 is line linear indutance and T471 is line output transformer. 240V voltage needed for field scanning is
transmitted via winding 10 of the transformer and gained after being rectified by VD472. In addition to anode
Circuit Explanation
