The secondary sound MF signals are input via pin 54 of OM8377, and then demodulated in PLL tuner through
lowpass and limit inside OM8377. 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 OM8377 pin 51, controlled by
CPU. A swith inside I2C bus control OM8377 can be used for options of internal and external signals. The sound
signals are transmitted via OM8377 pin 1 to TDA7523 pin 1 via C601 coupling and transmitted from its pin 4, after
being amplified by TDA7523, 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 OM8377 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 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.
(5) Field sync and output circuit
Field sync seperator produces field sync signals from compound sync signals and activates the field frequency
splitting system. When a certain number field sync pulse is detected, the field frequency spliting system will start
operation for frequency spliting of the muliple line frequency signals generated by the line frequency oscilator. The
field pulse gained from frequency spliting will be sent to field sawtooth generator for sawtooth waves, and then
transmitted by pin 23. The output circuit of this TV set is mainly comprised of TDA8357 and other components.
(6) CRT output circuit
The tricolor signals produced by OM8377 will be transmitted to CRT board and then to the cathode of the TV tube
after being amplified by videoamplifier which is comprised of V902, V912 and V922.
(7) CCD performance
Circuit Explanation
Summary of Contents for HTVF20R72
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