PURPOSE: To make it possible to start horizontal oscillation even when an AC voltage increases gradually, by actuating a horizontal driver circuit by making use of a blocking oscillation output.

CONSTITUTION: To point B, a DC voltage is applied by resistance R1 and capacitor C4, and transistor Q1 is applied at its base with a constant voltage divided by resistances R2 and R3. In the beginning when the DC voltage is applied from point B via capacitor C5, the emitter potential of Q1 is equal to a potential at point B, but once capacitor C5 is charged with the time constant of resistance R4 and capacitor C5, it falls gradually by a value equivalent to the charge. With the emitter potential of Q1 decreases below the base potential, Q1 conducts to flow a collector current through the primary winding of transformer T5, and it is positively fed back via capacitor C6, so that Q1 will momentarily be saturated to charge capacitor C5 via Q1. With capacitor C5 charged, the emitter potential of Q1 increases up to the potential of point B and Q1 turns OFF. Although this operation is repeated, a voltage induced across the secondary winding of transformer T5 is rectified and smoothed by diode D1 and capacitor C1 and then supplied as the starting power supply of horizontal oscillation driver circuit 3.