1 - 271.4.3 DBF (Dynamic Beam Focus) circuitSince the display is flattened, the focus becomes unequal between the center and circumfer-ence of the picture. To compensate for it, it is necessary to superimpose the parabola voltageof 370Vp-p in the horizontal cycle with the static focus (with the horizontal width is 396mm) andthe parabola voltage of 145Vp-p in the vertical cycle. The slight voltage that is generated fromthe parabola voltage generating circuit is amplified and reversed to generate the high voltagein order to keep the focus equal. This circuit is called DBF circuit.As shown in Fig. (16), the circuit is composed of the parabola voltage generating circuit IC601,amplifier section IC6A1 in the front step, Q7A1 to Q7B5 of amplifier section in the rear step,T7A1, and so on.Video periodFigure 15In case of the horizontal DBF :370Vp-pIn case of the vertical DBF :145Vp-pApprox. 350VVertical DBF Horizontal DBF90VQ7B1Q7B2Q7B4Q7B5R7A5R7B7R7B9IC6A1IC601DEFL-PROCESSORICOP-AMPQ7A1 R7A5R7A4R7A6T7A1R7A3To FBTQ7B3Figure 16
