Multiple frequency vertical scan system

A vertical scan control system for use in a cathode ray tube display having a vertical deflection yoke and a vertical deflection system including a saw-forming capacitor and an oscillator operative thereon to periodically charge the saw-forming capacitor and conductive element for discharging the saw-forming capacitor for producing vertical deflection current in the deflection yoke, said vertical scan control system comprising:

• sensing means coupled to said saw-forming capacitor for producing a sample vertical deflection signal representative of the current within the vertical deflection yoke;
• amplitude detecting means coupled to said sensing means for producing a control signal proportional to the amplitude of said sample signal;
• reference voltage means producing first and second reference voltages corresponding to first and second predetermined vertical deflection current amplitudes;
• comparator means having a first input coupled to said amplitude detecting means and a second input producing an output signal representative of the difference between signals applied to said first and second inputs;
• a switch for selectively coupling said first or second reference voltages to said second input of said comparator means;
• and
• amplitude means including an active element coupled to said saw-forming capacitor having a conduction level responsive to the output of said comparator means for altering the amplitude of vertical deflection current produced by the vertical deflection system by altering the discharge of said saw-forming capacitor.