Daewoo DTC-14D9T Service Manual

Also see for DTC-14D9T: Instruction manual

Contents

Daewoo DTC-14D9T Service Manual Manual pdf 30 page image

4For SECAM L and L’ the TDA9346/TDA9341 is switched to positive modulation via I2C bus. SECAM L’ transmission onlyoccur in VHF band I and have their picture and sound carrier interchanged, compared to SECAM L and PAL B/Gchannels. For SECAM’L the picture carrier is situated at 33.9 MHz and the AM sound carrier at 40.40 MHz. The IF PLLreference is tuned from 38.9 to 33.9 MHz, this is done via I2C Bus and the SIF filter is switched from channel 2 to channel1;this is done by pin 4 of TDA 9346.The tuner AGC time constant is slower for positive than for negative modulation, because the TDA9346 reduces its AGCcurrent. To make the AGC time constant even slower an extra series resistor R105 is added. To prevent IF overloadwhen jumping from a very strong transmitter to a weak transmitter a diode D103 has been added3. Source switchingVideo :The TDA9346/TDA9341 has only one external video input. The SCART video in pin (#20) is connected to the frontRCA video input.The controlling software via I2C bus selects the signal source :- Video signal from tuner ( Pin 40 ).- External video.- External SVHS from SCART.The sound source switching is done in the video processor part and in the AM demodulator by the -Controller via I2Cbus.The video processor pin 28 has multiple functions and provides in this applicationbus.- Deemphasis time constant- Audio monitor output- External AM input- Deemphasis time constant : The time constant is given by the capacitor C511,needer to obtain the 54 s time timeconstant for standarad PAL signal.- Audio monitor output : the nominal output signal is 500 mVrms, for all standards. The signal is also internallyconnected through to the audio switch. This signal is not controlled by the volume setting and can be used forSCART audio output.The signal is buffered to avoid influencing the deemphasis time constant and to adjust the output level.- External AM input : By software the deemphasis pin can be converted into an input pin. External AM signal forSECAM L/L’ is directly connected to this pin. In this configuration the FM sound is internally muted, DC levelremains at 3Vdc.An external sound signal of 500mVrms is applied to pin 35 via a coupling capacitor. The input impedance of this pin is25k‰ typical. Switching between internal FM, external AM or external audio from SCART is controlled internally bysoftware.FUNCTIONAL DESCRIPTION APPENDIXThe SAW filter ( SF1 ) has a double Nyquist slope at 38.9 MHz and 33.9 MHz needed for this multistandardapplication. The disadvantage of this choice is that a 5.5 MHz trap filter ( Z501 ) is needed to suppress the residualsound carrier in the video for B/G signals.