37
CIRCUIT SIGNALS PROCESSING
•
MF amplifying circuit
Received by antenna 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.
•
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.
•
Line sync processing circuit
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.
•
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 high pressure, screen
grid and focus voltages, the transformer provides 180V video amplifier voltage by
winding 2. VD411, C411, R412, VD412, R414 and C412 form the X ray protection
circuit. R233, C231, R232, R403 and C408 form the beam restriction circuit. The
winding 9 of the transformer provides CRT filament voltage.
