Daewoo DSC-3220E/3220L service manual Standard Features, FPLL, VCO and AFC

Page 46

Service manual SC-150

SAW filters

Ref.

Standard

Features

K3953M

B/G - D/K - I - L/L’

- IF filter for video application

 

 

- TV IF filter with Nyquist slopes at 33.9 MHz and

 

 

38.9 MHz

 

 

- Constant group delay

K9650M

B/G - D/K - I - L/L’

- IF filter for audio application

 

 

- TV IF audio filter with two channels

 

 

- Channel 1 (L’ ) with one pass band for sound

 

 

carrier at 40.40 MHz

 

 

- Channel 2 ( L, D/K, I, B/G) with one pass band for

 

 

sound carriers between 32.40 MHz and 33.40 MHz

5-2-3 Tuner-and VIF-AGC

At Pin 8, the VIF-AGC charges/discharges the AGC capacitor to generate a control Voltage for setting the gain of the VIF amplifier and tuner in order to keep the video output signal at a constant level. Therefore, in the case of all negative modulated signals (e.g., B/G standard) the sync. level of the demodulated video signal is the criterion for a fast charge/discharge of the AGC capacitor. For positive modulation (e.g., L standard) the peak white level of video signal controls the charge current. In order to reduce reaction time for positive modulation, where a large time constant is needed, an additional black level detector controls the discharge current in the event of decreasing VIF input signal. The control voltage (AGC voltage at Pin 8) is transferred to an internal control signal, and is fed to the tuner AGC to generate the tuner AGC current at Pin 11 (open collector output). The take over point of the tuner AGC can be adjusted at Pin 10 by a potentiometer or an external dc voltage (from interface circuit or microprocessor).

5-2-4 FPLL, VCO and AFC

The FPLL circuit (frequency phase locked loop) consists of a frequency and phase detector to generate the control voltage for the VCO tuning. In locked mode, the VCO is controlled by the phase detector and in unlocked mode,

the frequency detector is superimposed. The VCO operates with an external resonance circuit (L and C parallel) and is controlled by internal varicaps. The VCO control voltage is also converted to a current and represents the AFC output signal at Pin 22. At the AFC switch (Pin 19) three operating conditions of the AFC are possible:

AFC curve “rising” or “falling”an d AFC “off”. A practicable VCO alignment of the external coil is the adjustment to zero AFC output current at Pin 22. At center frequency the AFC output current is equal to zero. Furthermore, at Pin 14, the VCO center frequency can be switched for setting to the required L’ value (L’ standard). The optional potentiometer at Pin 26 allows an offset compensation of the VCO phase for improved sound quality (fine adjustment). Without a potentiometer (open circuit at Pin 26), this offset compensation is not active. The oscillator signal passes a phase shifter and supplies the in-phase signal (0o) and the quadrature signal (90o) of the generated picture carrier.

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Contents Chassis SC-150 Contents General description Main PCB Union PCB Sound Output Power Main FeaturesPower consumption Tuning systemSvhs Pin Signal Description Matching value Page C03 C01C02 C04639.25 S12 S10S11 S13Program Group Skip Special case Country selection = OthersITV Safety instruction RAY Radiation PrecautionParabola Order Default settingh for SC-150Alignment instructions HOR WidthOption HOR Paral BOW HOR Width Corner EW Trapez IC description VCTPage Page Chassis IC marking OSD languages Atss countries Text IC version VCT 3832A VCT 3834APin Name Type Short Description Gndaf Supply AGC Page Nicam plus FM/AM-Mono DSP-Section Audio Baseband ProcessingAnalogue Section German 2-Carrier System Dual FM SystemUssr PALSECAM-L AdrselDvss ResetqDvsup VREF2Testen FeaturesANAIN1 XtalinPin Symbol Function OUT1+ OUT1GND1 ModeTDA8946J Page GND Block diagram TDA6107Q SDA SCLPage IIN H Pin Name Symbol DescriptionVIN OVP TJ TSDDescription IC Pins Symbol Rating Unit I2C Decoder SW2 SW1SW0 SW3IN1 IN3OUT 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 Thermal shutdown circuit TSD Overcurrent protection function OCPLatch circuit 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 Jumper DEL Different Part List by PCB & Micom Version Main PCBUnion PCB JumperExplode View PCB Main PCB Union Schematic DiagramMAIN Schematic DiagramUNION

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