Hitachi 22LD3750DC Service Manual page 5

Teletext/OSD
• Simple Text 10 Pages
• Fastext & Top Text (OPT)
• Teletext Languages (ALL)
• Character Based OSD
Electrical features
•IPS generates 12V and 5V DC supply.
•<1W standby power consumption
System Building Blocks
17MB29 chassis main blocks are as follows:
•Analog Front End : VCTI (Microcontroller+Video Proccessor+Audio Proccessor+IF
Demodulator+ Teletext Decoder+ OSD Generator)
•Back End : MST-TSUMU38BF(Scaler, Deinterlacer, OSD Generator)
Analog Front End
17MB29 main board consists of two major blocks. The first block is analog front-end and this
block is handled by VCTI chip that is highly multifunctional. VCTI performs Tuner IF demodulation,
CVBS, RGB, SVHS and audio input selection and processing. The audio processor (MSP) supports
equalizer, tone control, volume control, AVL, surround effect etc. The video processor (VSP) handles
video processing such as color standard detection and demodulation, picture alignment (brightness,
contrast, color etc.). The IC also has a teletext decoder with fastext memory. The processed video output
is sent to MST-TSUMU38BF, scaler/deinterlacer in RGB format together with a composite sync.
The TV tuner is PLL controlled symmetrical IF output type. The IF signal is filtered by a single
SAW filter. Inter-carrier sound demodulation is performed by the system. After the SAW filter block, IF
signal is processed by VCTI IF demodulator. Audio signal is digitally filtered in the IF demodulator
block. The same IF signal is buffered and sent to DVB-T module card, tdm1300.Since VCTI can handle
all the audio processing, there is no need for additional audio processor solution on the board.
MSP has two audio inputs which are assigned to the Scart in L/R and Audio Switch L/R output.
MSP has three audio outputs which are assigned to the headphone amplifier L/R input, audio amplifier
L/R input and Audio switch L/R input. The board employs MP7721 and TDA1308 to drive speaker and
headphone outputs, respectively. Switching control for other audio inputs and outputs (HDMI, Back AV,
PC, DVD, and DVB-T) is achieved by an I2C controlled audio switch (TEA6422).
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