XOCECO PH-50T18, Service Manual

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9
Working principle analysis of the unit
1. TV board part
The audio signal from AV1, AV2, YpbPr2 send directly to AV switch (M52797), 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 of AV1 and AV2 send to AV switch 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 V2 OUT 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.
3. IC function, the internal block diagram, the pin introduction
3.1 PW2300
PW2300 is a piece of the front-end video-processing chip that integrates a high-powered,
multi-system video decoder with a high speech ADC module. All of the input video signal (except for
HDMI signal) are inputted to this chip to the AD switch and video decoding, 24 bit digital RGB signal