Disclosed is an image display screen controller for the control of a cathode-ray tube. There is produced a blanking logic signal that begins on a leading edge of the frame synchronization square-wave pulse and ends only on the trailing edge of the VFBACK signal generated from the frame flyback pulse without getting interrupted if the frame synchronization pulse and the pulse VFBACK corresponding to the frame flyback do not overlap. An RS flip-flop circuit is activated on the leading edge of the frame synchronization square-wave pulse VSYNC and is reset only by the trailing edge of the frame flyback pulse VFBACK. The output of the RS flip-flop is applied to an input of an OR gate that receives other inputs, notably the synchronization square-wave pulses and the line and frame flyback pulses. If the scanning disappears for example by the destruction of a transistor, the absence of a frame flyback pulse will prevent the reactivation of the beam and hence prevent a dot of the screen from being burned out.