Zenith C32V23 Service Manual

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

PV154 - 923-03497 3-4 AB - SERVICINGSERVICINGA sensing resistor inside of TX3201 provides a DC voltageproportional to the CRT anode voltage and is used like aprimary feedback for the HV compensation circuit. Asecondary winding on TX3201 (pin 6) provides a lowvoltage flyback pulse (H-FLYBK) used for synchronizationof the Scan Boost Converter and the HV Compensationcircuit. A capacitive divider, CX3205 and CX3206, providea low voltage flyback pulse (H-FBP) used forsynchronization, phase comparison, etc.The linearity coil L3200 is saturating inductor skewedby a permanent magnet bonded to the coil. It producesa non-linear inductance curve vs current. Thischaracteristic cancels non-linearity in the deflectioncurrent caused by horizontal deflection coil resistance.BASE DRIVE(Refer to figure on the next page). The Base Drive(Proportional Drive) circuit provides high forward andreverse current to drive the base of the horizontal outputtransistor QX3200 from a low level input (H-DRV fromthe deflection processor ICX2600 in main chassis). Thissignal is approximately 9 Volts peak to peak at theoperating frequency and has a duty cycle of about 40%high, 60% low.Current from H-DRV is amplified by transistors Q3203and Q3204 providing low impedance to rapidly drivethe gate of the driver transistor Q3205. This action resultsin an alternating current flow in the primary of drivertransformer T3200. During Q3205 on time energy is storedin T3200 and rapid turn off of QX3200 is initiated. DuringQ3205 off time the energy previously stored in T3200 isused to drive the base of QX3200. A winding in T3200from the emitter of QX3200 to ground provides pulseshaping to optimize the base drive and improve efficiency.HV COMPENSATIONA resistor inside of the sweep transformer senses the CRTanode voltage (Pin 14). The DC voltage appearing onthis resistor is used in one of the operational amplifiersof IC3101 to provide the error voltage needed to regulatethe HV to a specified level.The error voltage is compared with a ramp signalgenerated in one comparator of IC3100 and sinchronizedby the flyback pulse (H-FLYBK) at horizontal scanningfrequency to modulate the pulse width in the output todrive the gate of the switching transistor Q3103. Thisramp signal is present only during the flyback pulse.Q3103 is on during the scan time and as long as theerror voltage is higher than the ramp signal. This allowsenergy to be stored in TX3100. When Q3103 is turnedoff, the resonant circuit formed by C3109 and the primaryinductance of TX3100 produce a flyback voltage of about400 volts peak resulting from the stored energy inTX3100.This voltage is induced to the secondary windings ofTX3100 to add to the voltage generated in the horizontaldeflection circuit. This induced voltage is used tocompensate load variation (beam current variation) inthe HV flyback transformer TX3201. RX3335(potentiometer) is used to adjust the high voltage to aspecified level. (Refer to the figure on the next page).SHUTDOWN CIRCUIT OPERATION(Refer to figure on the next page). The flyback pulsevoltage from pin 6 of TX3201 (flyback transformer) ispeak detected (rectified) by the action of diode D3000and capacitor C3001. This forms a DC voltage appearingon C3001 representative of the CRT anode voltage (HV)produced by TX3201. This voltage is divided down byprecision resistors RX3001, RX3002, and RX3003. Thislower voltage appears on the positive input (pin 5) ofIC3101. In the event the CRT anode voltage becomesexcessive, in IC3101 the positive input (pin 5) will behigher than negative input (pin 6) and therefore thisoutput (pin 7) will go to high level at approximately 15volts. This signal (SD-DRV) is sent to the base of Q3201causing the horizontal drive to be disabled and latchedcausing HV to goe down. In about 5 seconds theshutdown reset circuit (Pins 8, 9 & 14 of IC3100) enablesthe horizontal drive and HV must be reestablished. Ifthe shutdown condition persists, the circuit goes intohiccup mode. The circuit formed by Q3104, C3113,C3108, D3107, R3131, R3132, R3133, and R3134 disablethe HV compensation output (Q3102-B signal) duringturn on and shutdown conditions (transients).VERTICAL DEFLECTION(Refer to figure on the next page). The vertical deflectioncircuit (ICX2100) is a linear amplifier that can directlydrive the yoke current (including the required DCcomponent). The sawtooh waveforms needed as inputsby ICX2100 are generated in the Deflection ProcessorICX2600. V-PROT is an image of vertical deflection currentand it is used by the Deflection Processor to protect theCRT.