Working Principle Analysis Of The Unit - Prima LC-20S3 Service Manual

Working principle analysis of the unit

The set is multi-media LCD TV boardcast receiver, it contain PAL/SECAM B/G,I,D K L L' of color
system, and AV input, S-VHS input, PC,VGA,DVI and earphone output terminals. The power
circuit is built-in, it adopt the power manage chip STR-W6856N of the SANGKEN company, output
the 12v and 18v voltage, provide a 12V for the picture processing and 18V for sound amplifier.
It is composed of the power board and the video signal digital image processing.
VCT4993R (N102) is a integrative chip of digital IF amplifier, video decode, sound processing,
image processing and CPU, it has teletext decode function and 8M FLASH (N103) and 1M SRAM,
there can deposit 250 page teletext.
FR signal via the image IF signal of the tuner TUNER101, the signal is send to PIN109 and PIN110
of multi-system video/sound signal of N102 VCT4993 via Z103 of SAWF (Surface Acoustic Wave
Filter), IF signal is demodulated for image and sound, output a composite video signal, then select
switch signal source for video and s-video of AV board and RGB signal of SCART of the main board,
it send to digital image processing chip (MST519VA) via image processing (ITU656 of digital
signal).
After sound of DVI and YPBPR via switch selection N301 HEF4052, this signal and sound of the AV
and SCART, with sound of demodulation IF via internal switch selection, and stereo processing
from PIN124 and PIN125 of VCT4993 (N102) output, then sent to sound amplifier (N504) of the
power board, it is amplified for speaker.
MST519VA (N202) is digital image processing chip, it process the YPBPR, VGA, DVI signal and the
ITU656 signal from VCT4993 (N102), through auto ADC correction and internal arithmetic
processing, then outputs 24 BIT TTL level RGB signal to socket X202. Through N501 cable, the
signal is sent to LCD panel interface to perform reproduction of image.
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