Zenith C32V23 Service Manual

Also see for C32V23 - 32" Flat-Screen Integrated HDTV: Operating guide & warranty

PV154 - 923-03497 3-3 AB - SERVICINGSERVICINGDEGAUSSINGThe ADTV chassis employs an innovative method ofdegaussing, just like former Zenith TVs it is performedthrough software in order to obtain a properdemagnetization for these screens.IC6000 generates a pulse about 1 second on pin 48 setto high (about 4.8 VDC) through RX3900 (4.7K 5% ¼watt).It is applied to QX3900, which drives the 12 VCD relayKX3900 in series with a current limiting resistor. So thedegaussing is performed when the degauss coil is pluggedto the 4T8 connector ends.HORIZONTAL & VERTICAL DEFLECTIONThe AB chassis was designed to support only onehorizontal frequency for DTV, 33.75Khz. It supplyshorizontal and vertical currents to the deflection yokecoil and the high voltage generation for the CRT. Thissection is dependent on other circuits in the mainchassis to provide drive signal, DC control voltage,s anddeflection corrections. This section can be divided into6 functional blocks:• Horizontal Deflection and HV Generation• Base Drive• HV Compensation• Shutdown Circuit• Vertical DeflectionHORIZONTAL DEFLECTION AND HV GENERATIONThe Horizontal Deflection circuitry is a common flybacktopology used in many television and monitorapplications. QX3200 is the Horizontal Output Transistor.When QX3200 is initially turned on, current is allowedto flow from the B++ supply through TX3100, TX3201,and QX3200. This allows energy to be stored in TX3201.When QX3200 is turned off some of this energy is returnedto charge the S-capacitor(s) CX3208, CX3210, and C3232.After several cycles (repeating at scanning frequency)sufficient voltage appears across the S-capacitorsproviding an additional path producing current flowthough the horizontal deflection yoke coil (connector4X4). The negative current path is provided by thedamper diode DX3200. The result is a positive andnegative sawtooth current through the horizontaldeflection coils (approximately 11 to 17 Amps peak topeak). When QX3200 is turned off, about 1100 Voltspeak of flyback voltage is produced resulting from thestored energy in the horizontal deflection coils andTX3201. This voltage is induced to secondary windingsof TX3201 to generate the high voltage from 28 to 30KV. The flyback (or retrace) period is about 5.0 s.Horizontal Deflection and HV Generation Block Diagram