| 摘要 |
PURPOSE:To keep the initial quality of a picture by detecting a vertical displacement of an electron beam on a screen and feeding back the detected data to a part of a drive circuit to keep the electron beam to aprescribed vertical position at all times. CONSTITUTION:Four bar form detection metal backs A1, B1, B2, A2 are provided on a screen on which a fluorescent substance is coated in stripe form vertically and a metal back layer is added. Outputs of the detected metal backs A1, B1, B2, A2 are sampled by sampling circuits 53-56 through an isolation 52, A/D-converted and stored by initial value memories 61-64 as the initial value data respectively. Then the detection data during the blanking period is stored sequentially in detection memories 65-68 and the detection value data is compared with the initial value data by using a microcomputer 69. Then a vertical deflection data memory 27 is rewritten in response to the result of comparison so as to correct the position of the electron beam. |
