Abstract: When a “screen saver” operates to display a homogeneous black picture image after the same image is continuously displayed on a CRT for a predetermined period of time, a power supply for a CRT display unit is controlled to be turned off, thereby preventing the CRT display unit from being left for a long time in a power-on state. Namely, a waiting time of 3 minutes, for example, is provided when the “screen saver” operates so that the CRT displays a homogeneous black picture image to turn off a power circuit for the CRT, and then a heater for the CRT is turned off after a lapse of a predetermined period of time of 5 to 60 minutes, for example. An extension graphics board, which is inserted in an open slot provided in a computer of an open architecture type may be provided to perform this function.

Abstract: In order to eliminate any harmful influence due to electric field radiation on the human body, electric field radiation from a front surface of a cathode ray tube is reduced. A degaussing coil arranged in proximity to a peripheral edge of a front surface of a cathode ray tube is employed advantageously. The degaussing coil is supplied with a voltage which is opposite in polarity to an electric field radiated from the front surface of the cathode ray tube. The reverse polarity voltage is derived from an output signal obtained from an output signal of a horizontal deflection circuit by a flyback transformer and/or derived from a voltage obtained by phase-inverting an anode voltage fluctuating in vertical synchronization.