Vertical deflection circuit with service mode operation

A vertical deflection circuit of a video display apparatus having normal and service modes of operation, comprising;

• a vertical deflection winding;
• an amplifier responsive to a sawtooth signal and having a driver stage that is coupled to said deflection winding for generating, during normal operation, a sawtooth deflection current in said deflection winding;
• and
• a sawtooth signal generator for generating said sawtooth signal, said sawtooth signal generator including:
• a source of a first voltage developed during said normal and during said service modes of operation;
• a first capacitance coupled to said source of said first voltage;
• a source of a first control signal at a frequency that is related to a deflection frequency;
• a first switch responsive to said first control signal and coupled to said first capacitance, said first switch operating at a frequency that is related to that of said first control signal during both said normal mode of operation and said service mode operation, for discharging, in said normal mode of operation, said first capacitance via said first switch during a first portion of a given period of said first control signal;
• a source of a second control signal having a first state that is indicative when said normal mode of operation is required and a second state when said service mode of operation is required;
• and
• a controllable impedance responsive to said second control signal and coupled via said first capacitance to said source of said first voltage for providing, in said normal mode of operation, a current path to a current that charges said first capacitance during a second portion of said given period to produce said sawtooth signal at a second terminal of said first capacitance, and for decoupling said current path from said second terminal of said first capacitance when said second control signal is at said second, service mode operation state to prevent the charging of said first capacitance for preventing the generation of said sawtooth signal and said deflection current.