What does the shutdown circuit do?
ANSWER. The shutdown circuit is a solid-state set’s overvoltage protection. Excessive voltages lead to excess heat, arcing, component breakdowns and even fire. A more insidious result of overvoltage is excessive x-radiation from the picture tube. The overvoltage circuit takes a voltage measurement near the horizontal output transistor. If voltage at this point measures high enough to switch a trigger diode, an SCR fires. This SCR is usually part of a crowbar circuit. This circuit blows a line fuse or disables the horizontal oscillator circuit. In either case, the TV set powers down. Before the set can operate normally again, it requires service. Overvoltage projection is also one reason why manufacturers allow no parts substitution in certain circuits. Among these circuits are…
