Daewoo Color Television Service Manual

Contents

Daewoo Color Television Service Manual Manual pdf 32 page image

5. SECAM L/L' sound switching circuit.The microcontroller pin 4 is a three levels output. The voltage and configuration of this port is described below :In FM mode the microcontroller is internally grounded to pin 4. The TDA9830 output is muted6. Sound amplificationThe device TDA7267A is a mono audio amplifier in powerDIP package specially designed for TV application. Thanks tothe fully complementary output configuration the device delivers a rail to rail voltage swing without need of bootstrapcapacitors. No external heat sink is needed as the Cu ground plane of the PCB is used as heat dissipation.7. Vertical deflectionThe vertical driver circuit is a bridge configuration. The deflection coil is connected between the output amplifiers, whichare driven in phase opposition. The differential input circuit is voltage driven. The input circuit is especially intended fordirec connection to driver circuits which deliver symmetrical current signals, but is also suitable for asymmetrical currents.The output current of these devices is converted to voltages at the input pins via resistors R350 and R351. The differentialinput voltage is compared with the output current through the deflection coils measured as voltage across R302, whichprovides internal feed-back information. The voltage across R302 is proportional to the output current.Flyback voltageThe flyback voltage is determined by an additional supply voltage Vfb. The principle of operation with two supply voltages(class G) makes it possible to fix the supply voltage Vp optimum for the scan voltage and the second supply voltage Vfboptimum for the flyback voltage. Using this method, very high efficiency is achieved. The supply voltage Vfb is almosttotally available as fly-back voltage across the coil, this being possible due to the absence of a coupling capacitor.ProtectionThe output circuit has protection circuits for :- Too high die temperature- overvoltage of output stage AGuard circuitThe guard signal is not used by the TDA9361/ TDA9381 to blank the screen in case of a fault condition.Damping resistorFor HF loop stability a damping resistor (R305) is connected across the deflection coil.6FUNCTIONAL DESCRIPTION APPENDIXSound mode Port configuration VoltageFM Push Pull Internally shorted to groundAM L Push Pull Pull up to 3.3VAM L' High Impedance Fixed by R511, R156, R157