Automatic correction of centering and convergence errors in CRT displays

A system for the automatic correction of centering errors in a cathode ray tube display, said display having a major axis and a minor axis perpendicular to one another, said system comprising:

• a first masked light sensor positioned on said major axis and a second masked light sensor positioned on said minor axis, said first and second light sensors being located outside the field of view of said display but within the scanned area;
• light blip generator means responsive to horizontal and vertical timing pulses supplied to said cathode ray tube display for unblanking the video circuits during the horizontal and vertical blanking intervals to thereby generate light pulses in the vicinities of said first and second light sensors;
• and
• microprocessor feedback controller means responsive to the outputs of said first and second light sensors and connected to centering circuits in said cathode ray tube display for iteratively generating correction signals to the centering circuits whenever no output is received from one or the other or both of said first and second light sensors.