Daewoo 2898ST Service Manual

Also see for 2594ST: Instruction manual

Contents

Daewoo 2898ST Service Manual Manual pdf 46 page image

46failure ( “ Power-On Reset “ bit POR ) is detected.The power failure may have corrupted the contents of the internal data registers, so the TDA8375A should bestarted up again.The TDA8375A has a separate supply input (pin 37) that only used as a clean supply voltage for thehorizontaloscillator circuits.Vertical synchronizationThe vertical sawtooth generator drives the vertical output.It uses an external capacitor at pin 51 and a current reference resistor at pin 52.The TDA8375A vertical drive has differential current outputs for DC-coupled vertical output stage, like the TDA8351 .At TDA8351 input pins l and 2 this current is converted into a drive voltage via a resistor.Geometry processingWith the TDA8375A is possible to implement automatic geometry alignment, because all parameters are adjustedvia the I2C bus.The deflection processor of the TDA8375A offers the following five controls;- Horizontal shift- Vertical slope.- Vertical amplitude- Vertical S-correction- vertical shiftColour decoderThe colour decoder contains an alignment-free X-tal oscillator, a dual killer circuit and colour difference demodulators.Together with the TDA8395 SECAM add-on a multi standard PAL/SECAM/NTSC decoder can be built withautomatic recognition.Which standard can be decoded depends on the external Xtals used.Two Xtal pins (34and 36) are present so normally no external switching is required.The I.C. must be told which X-tals are connected (bits XA and XB).This is important, because the X-tal frequency of the colour decoder is also used to calibrate many internal circuit.The burst phase detector locks the Xtal oscillator with the chroma burst signal.The phase detector operates during the burst key period only, to prevent disturbance of the PLL by the chroma signal.Two gain modes provide:- Good catching range when the PLL is not Locked.- Low ripple voltage and good noise immunity once the PLL has lockedThe killer circuit switches-off the R-Y and B-Y demodulators at very low input signal conditions (chroma burst amplitude).A hysteresis prevents on/off switching at low, noisy signals.Color standard pin34 pin35 XA XBPAL4.43/SECAM + NTSC-4.43 none 4.43 1 0PAL4.43/SECAM + NTSC-M 3.58 4.43 1 1Integrated video filtersThe TDA8375A has alignment-free internal luminance delay, chroma bandpass and chroma trap.They are implemented as gyrator circuits tuned by tracking to the frequency of the chroma Xtal oscillator.The chroma trap in the Y signal path is by-passed when Y/C input is selected (S-VHS ).For SECAM an extra luminance delay is build-in, for correct delay of the luminance signal.