Briefing On Lc20H15 And Its Working Principle - Polaroid LC20H15 Service Manual

Briefing on LC20H15 and its working principle

LC20H15 multi-media liquid crystal TV broadcast and receiving set adopts liquid crystal display
screen of LG 20.1, which is provided with NTSC color system receiving function in addition to AV
input,S-VHS input,high definition signal port for component YPrPb/YcbCr,PC VGA port, earphone
output and other signal ports. For power supply an externally connected power adaptor is provided.
The circuitry of LC20H15 is composed of RF module board, video signal board, digital signal picture
processor and AC-DC transformer, and DC-DC circuit board.
The working process is as follows. The radio frequency signal undergoes an integrated tuner U1
before a color full video signal is generated. This video signal then enters analog board decoder IC N1
VCT3833 Pin19 where it is processed and it's output as analog signals R, G, B through Pin42, PIN43,
PIN44. Audio frequency signal is processed with sound in IC N1 VCT3833 Pin19 and then output
through MSP3420G Pin28 , Pin27 to SRS for surround sound processing in IC N6 M62494E. Finally it
is subject to power amplification in IC N8 TDA3002D2 before it is output to speaker.
VGA signal/high definition signal is input to personal computer through the main board. The signal
selected by Y/Pb/Pr through 5 way 1/2 switches IC(U9 BA7657F)is subject to reselection together with
signal TVRAIN, TVGAIN, TVBAIN through 5 way 1/2 switches IC(U7 BA7657F). Finally signals R, G, B
are selected and sent to the main processing chip PW1306.
PW1306 is a built-in X86 CPU of the main processing IC,externally connected by 8M Flash(U13)
memory to control the whole system. The input signal of V-port and G-port is subject to internal
arithmetic processing and then output as R, G, B signals with electric level of 24 bit TTL to sockets JP3
and JP4, where through connection wires the signals are sent to the port of LG liquid crystal screen
and for the realization of picture reproduction.
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