XOCECO PH-50HU31S, Service Manual

6 

Working principle analysis of the unit

The RF signal received by antenna will be sent to tuner TUN401, then IF signal will be obtained 

through high amplifier and mixed frequency, through pre-intermediate amplified by V408, then it will 
be sent to acoustic surface-wave Z407 to do IF filter and get better IF characteristics, then it will be 
sent to N404 (TDA4470) to do intermediate amplification, phase-locked loop VCO and synchronous 
wave detection to get video signal TV-V; after pre-intermediate amplification IF will also be sent to 
acoustic surface-wave Z406 to do filter at the same time, then it will be sent to N404 to do 
intermediate amplification and output the second sound intermediate frequency signal (TV-SIF). 

The TV-V signal output from TDA4470 together with TV-SIF will be sent to main IC 

NS4(MST9E88L).  

Video signals of AV1/S, VGA, YPbPr and HDMI will be sent to MST9E88L, too. 
Video RGB of SCART1 and S-Y, S-C of SCART2 will still be sent to MST9E88L, and the audio 

signal of them via audio switch N302(HEF4052BT) selection after also sent to MST9E88L. 

The main IC NS4(MST9E88L) is a high performance and fully integrated IC, which can realize 

HDMI processing, video demodulating, video switch selection, A/D and D/A conversion, 
interlace/de-interlace processing, modes conversion, OSD and low-voltage differential output, ect. 
And it also has functions of audio selection, processing and MCU. 

The video signal via MST9E88L processing, output 4 pairs differential signal and 1 pair clock 

signal for 

P

D

P

 panel display. TV-V output from TDA4470 via double video amplifying, it will be sent 

to SCART1 for AV-OUT. AV processed by MST9E88L via double video amplifying will be sent to 
SCART2 for AV-OUT, too.   

Audio signal via MST9E88L processing will be sent to sound amplifier N405 (MP7722DF) 

amplifying to speaker. The audio also sent to earphone amplifier N406(BH3547F) amplifying to 
earphone. TV audio signal will be sent to D/A converter NS6(DS4344) through I2S bus converting to 
analog audio signal TV-L/R, then sent to SCART1 for AV-OUT. At the same time, TV-L/R together 
with AV-L/R processed by MST9E88L will be sent to audio switch NS8(HEF4052BT), after selecting 
to SCART2 for AV-OUT.