XOCECO LC-32FC18, Service Manual

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8
Working principle analysis of the unit
1. Starting of the system
The system adopts 264MHz, 32bit MIPS CPU of Linux operating system. It needs bootstrap routine
to start the unit after power-on, which stored in N142 (serial Flash in the block diagram). After
bootstrap routine finish, start the Linux operating system and application programs from N141
(Nand Flash).
2. Video signal flow
Antenna reception signal send to digital-analog integrative tuner (contain HF and IF amplifier circuit),
which integrate decoder for analog NTSC, direct output NTSC composite video signal, and
integrate digital IF amplifier circuit. The tuner is controlled by the command (SDA and SCL) of N1
(X240H), select appropriate channel to store the signal into X240H. For the channel resource is
fixed, it can’t transmit the analog and digital program at the same time, X240 reception signal from
the tuner is analog CVBS (NTSC program) or the digital differential IF signal (ATSC/Clear QAM
program), only one of them. The digital IF signal is demodulated and MPEG decoded in X240.
AV and S-video signal via matched component direct send to N1 (X240H) video switch, A/D
conversion and digital decode; YPbPr via matched component send to video switcher
N701(PI5V330Q), the selected signal and D-Sub signal send to N502 (AD9880) ADC, then output
24bit RGB/YCbCr 4:2:2 to N1; HDMI also via N502 (AD9880) output 24bit YCbCr 4:2:2 to N1.
The all video signals (contain DTV video) send to X240H image scale and OSD superposition, then
output RGB signal of 24bit to LVDS switcher N561 (THC63LVDM83R), in there the signal is
converted into 3 pairs low voltage differential signals and 1 pair clock signal, then send to LCD
panel.
3. Audio signal flow
Sound signal (SIF, AV sound, YPbPr and D-Sub) via NB04 HEF4052BT (sound diverter switch) to
output signal, it send to N201 (MPS4440G on 53# board) sound processing and switch of audio,
select I2S digital audio signal, send to X240H video-sound synchronization, then send back to N201.
Likewise, I2S audio signal of HDMI send to X240H video-sound synchronization, then send back to
N201.
At last, sound signal send to N201 D/A convert and process of sound effect. Select left/right audio
channel, their send to sound amplifier NV01 (TPA3008) amplify, then send to speaker.
4. Function of ATMEGA 8
a. key scan and infrared control
b. power on/off
c. VGA
control
d. Brightness control of backlight
e. Timing
N801 communicates with N1 (X240) by UART