CRT Preset Focus
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Available color CRT displays require setting of individual electrode voltages for precision focussing by adjusting resistance values in a resistor divider chain during assembly of the display. This disclosure enables this setting to be carried out by the CRT manufacturer on a resistor chain deposited on the CRT glass with resistance adjustment by laser trimming. Color CRT requires bias voltages to set focus, G2 and the three cathode black levels, which differ from one CRT to the next. In existing display designs these voltages are produced from potentiometer circuits. Focus and G2 come from high voltage resistors plus mechanical potentiometers, usually mounted on the flyback transformer and tapped off the final anode high voltage point.