Working Principle Analysis Of The Unit - XOCECO PH-42T8 Service Manual

Working principle analysis of the unit

1. TV board part
This set adopt all system for integrative tuner (include high frequency and intermediate frequency
amplification circuit), the antenna receive the signal and send to the tuner, the tuner is controlled
N602 PW118 MCU (by SDA, SCL), and select the appropriate channel, switch the right mode, after
the high frequency amplification and intermediate frequency amplification, output the video and
audio signals.
The audio signal output by the tuner send directly to AV switch (M52797), select this signal and the
audio signal from AV1, AV2, YPbPr, output the audio signal of the selected channel and separate to
two ways; one way after amplifying 6 db is AU OUT; another way send to audio and sound
processor IC N907 R2A15900. In R2S15900, such signal and audio signal of VGA, HDMI, YPbYr1
are selected by MCU, and output the signal by volume and treble-bass control into D type power
amplifier to amplify, finally output to sound box and represent the sound. When insert the earphone,
the jack of the earphone with the switch send the left/right track of the output of R2S15990 to the
earphone power amplifier N908 NJW1109, after amplifying, when use the earphone output to the
earphone jack to listen (the earphone can select by the customer's request).
The sound power amplifier MPS7720 is the high effective D type of power amplifier of the single
track. The output power can reach 20W without radiating fin, provided with the protective function of
overcurrent and overheat, when the direct-to-ground input is shorting, it can protect automatically
and stop outputting. If it has been not shorting, it can resume normal circumstance. Therefore,
when plug and play the audio cable (do not suggest such operation), if the set have no sound
because of incautious shorting, it will get right as long as you restart it.
2.The picture part
The video signal outputted by the tuner send to AV switch M52797 (N903), input the video signal of
AV1 and AV2 to M52797 (N903), and switch to gain two group of video output. One group output of
video signal sends to the AV-OUT terminal with its sound output and treat them as the AV OUT
output. Another group output of video signal send to PW2300 and make the video decoding, then
the video signal of S-VIDEO, YpbPr1, YpbPr2, VGA send to PW2300 (N700) synchronously. All of
these video signals shall be sent to this chip to make the video decoding or the AD conversion, and
then output the 24bit digital RGB signal and the related sync signal. PW2300 (N700) complete
mostly the function of 3D comb filter, the channel switch, 5 line Y/C separation, the colour decoding,
and so on. 24 bit digital RGB signal and the related sync signal are outputted by PW2300 (N700)
and are inputted to the next step chip PW118 (N602). The HDMI signal is inputted to AD9398 (N208)
to make the decoding, at the same time 24 bit digital signal and the related sync signal are
outputted and sent to PW118 (N602) to make the processing. PW118 is the new high-powered
image manipulation chip of Pixelworks. The 24 bit digital RGB signal and the related sync signal
outputted by AD9398 and PW2300 shall be inputted to this chip to make the image manipulation. In
addition to the function of interlaced to line-by-line, this chip further include the function of image
enhancement, etc.. PW118 can make the format switch for the different format inputted signal
(under the customer's request select SCALER function), and accord with the format request of the
screen, and output the low-voltage difference signal of digital RGB LVDS, and then send to the
screen and drive the screen. PW118 is the main CPU as well, the procedure store in external flash
MX29LV800 N404. The software update of RS-232 is that update the stored content of the N404 by
PW118.
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