akira 21WHBN, Service Manual

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9
Model No: 21WHS3BN
Version 1.0
THE HORIZONTAL AND VERTICAL CIRCUIT
Through Synchronous separating circuit, the video signal is divided into horizontal-Synchronizing
signal and Vertical-Synchronizing signal. The horizontal-Sync pulse coming from the pin 33 is
transferred to the horizontal-drive transistor, and will be used to drive the horizontal-transformer. The
horizontal-switch transistor is V451, it and the +B supply drives the flyback transformer to generate
the anode high voltage, the focus voltage, the screen voltage, the CRT board drive voltage 190V, the
vertical drive voltage 15V and -15V.
The vertical sawtooth wave is generated on the pin 21 and 22, and then enters the vertical output
amplifier circuit. The vertical output amplifier circuit is realized with the power amplifier IC –
LA78040 or STV9302A.
The STV9302A is a 7 pins vertical deflection circuit (3 Amperes) for DC-coupled 90° deflection
systems with frame frequencies of 50 or 60 Hz. Two single supply voltages for the scan and two
supplies for the flyback are needed.
The vertical drive currents of TDA9381 pins 21 and 22 are connected to input pins 1 and 7 of the
STV9302A. Pin 2 is the +15V DC power supply voltage, Pin 4 is the -15V DC power supply voltage.
The outputs (pin5) is connected to the series connection of the vertical deflection coil and feedback
resistor R406. The voltage across R406 is fed via pin 1 to obtain a deflection current which is
proportional to the drive voltage.