| 摘要 |
PURPOSE:To prevent white glitter on the left end of screen at mis-focussing, by clearing a monostable multivibrator in front of the effective screen with a low band signal from a photo detector, in a color receiver of beam index type. CONSTITUTION:A flip flop 43 is reset at the time point of the beginning of horizontal scanning start normally, the signal PX is obtained, a monostable multivibrator 46 is cleared with the output CP of the counter 45 obtained at the end of horizontal scanning start, and the switch 27 of the power supply 28 to drive the first grid 13 is cut off. At mis-focussing, at the start of hoirzontal scanning start, the flip flop 43 is not reset, but the light of index fluorescent stripe at the horizontal scanning start is detected at a photo detector 21, a signal PX is obtained through a low pass filter 51 to enable to clear a monostable multivibrator 46. Accordingly, even at mis- focussing, white glitter of the left end of effective screen, i.e., the start part, due to a given beam current is prevented. |
