Vertical deflection circuit with service mode operation.

摘要

In a video display apparatus having a service mode capability, a vertical deflection circuit (20) includes a vertical deflection winding (1 ) coupled to a DC blocking capacitor (CV). An output stage (21) is coupled to the vertical deflection winding (1 ) at an output terminal (A). A vertical sawtooth voltage generator (26) is coupled to a driver stage (22) for driving the output stage (21) at a vertical rate in a sawtooth manner to generate a sawtooth deflection current (iV) in the deflection winding (LV) and for establishing a DC operating voltage level (VO) at the output terminal (A) that charges the DC blocking capacitor (CV). The sawtooth generator (26) includes a second capacitor (C2) that, during normal operation, is charged in a sawtooth manner via a resistor (R11) for developing a sawtooth signal. A service mode switching circuit (50) is coupled to the resistor (R11) for asserting the service mode of operation by preventing the charging of the second capacitor (C2) via the resistor (R11). A DC feedback loop maintains the DC blocking capacitor (CV) charged during the service mode.