Daewoo DSC-3220E/3220L service manual

Page 48

Service manual SC-150

5-3 Video - VCT description

5-3-1 Introduction

The VCT 38xxA includes complete video, display, and deflection processing.

All processing is done digitally, the video front-end and video back-end are interfacing to the analogue world. Most functions can be controlled by software via I 2 C bus slave interface.

5-3-2 Video Front-end

This block provides the analogue interfaces to all video inputs and mainly carries out analogue-to-digital conversion for the following digital video processing. Most of the functional blocks in the front-end are digitally controlled (clamping, AGC, and clock-DCO). The control loops are closed by the Fast Processor (‘FP’) embedded in the video decoder.

5-3-3 Input Selector

Up to seven analogue inputs can be connected. Four inputs are for input of composite video or S-VHS luma signal. These inputs are clamped to the sync back porch and are amplified by a variable gain amplifier. Two chroma inputs can be used for connection of S-VHS carrier-chrominance signal. These inputs are internally biased and have a fixed gain amplifier.

5-3-4 Clamping

The composite video input signals are AC-coupled to the IC. The clamping voltage is stored on the coupling capacitors and is generated by digitally controlled current sources. The clamping level is the back porch of the video signal. S-VHS chrominance is also AC-coupled. The input pin is internally biased to the center of the ADC input range. Each channel is sampled at 10.125 MHz with a resolution of 8 bit.

5-3-5 Automatic Gain Control

A digitally working automatic gain control adjusts the magnitude of the selected baseband.

5-3-6 Digitally Controlled Clock Oscillator

The clock generation is also a part of the analogue front-end. The crystal oscillator is controlled digitally by the control processor. The clock frequency can be adjusted within ± 150 ppm. This adjustment is done in factory for every TV set.

5-3-7 Analogue Video Output

The input signal of the Luma ADC is available at the analogue video output pin (#11). The signal at this pin is buffered by a source follower. The output voltage is 2 V. The magnitude is adjusted with an AGC in 8 steps together with the main AGC.

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Contents Chassis SC-150 Contents General description Main PCB Union PCB Main Features Power consumptionSound Output Power Tuning systemSvhs Pin Signal Description Matching value Page C01 C02C03 C04639.25 S10 S11S12 S13Program Group Skip Special case Country selection = OthersITV Safety instruction RAY Radiation PrecautionOrder Default settingh for SC-150 Alignment instructionsParabola HOR WidthOption HOR Paral BOW HOR Width Corner EW Trapez IC description VCTPage Page IC version VCT 3832A VCT 3834A Chassis IC marking OSD languages Atss countries TextPin Name Type Short Description Gndaf Supply AGC Page DSP-Section Audio Baseband Processing Analogue SectionNicam plus FM/AM-Mono German 2-Carrier System Dual FM SystemPAL SECAM-LUssr AdrselResetq DvsupDvss VREF2Features ANAIN1Testen XtalinPin Symbol Function OUT1 GND1OUT1+ ModeTDA8946J Page GND Block diagram TDA6107Q SDA SCLPage Pin Name Symbol Description VIN OVPIIN H TJ TSDDescription IC Pins Symbol Rating Unit I2C Decoder SW1 SW0SW2 SW3IN3 OUTIN1 IN2VEE Circuit description If section Block diagram Vision if Amplifier Standard Features FPLL, VCO and AFCPage Page Adaptive Comb Filter VCT3834A only Video Sync Processing CRT Measurement and Control Page Configuration Stand byDescription Application Forced KEY Page ESC Quadrature MixersPage Page Power supply primary part operations STR-F6654 general descriptionPage STR-F6654 oscillating operation Overcurrent protection function OCP Latch circuitThermal shutdown circuit TSD Overvoltage protection circuit OVPTV start-up operations TV normal run and stand-by mode operations Page FBT SC-150 Controlled Rectifier 6V DC High Service Parts List Cord Power Oxide Film 2W 1.2 OHM J Small Semi Fixed CCZB1H561K Cera Carbon Film Metal Film Carbon Comp PA01A RF27 RD-4Z221J Different Part List by PCB & Micom Version Main PCB Union PCBJumper DEL JumperExplode View PCB Main PCB Union Schematic DiagramMAIN Schematic DiagramUNION

DSC-3220E/3220L specifications

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