故障现象 束流超过180μA，偏压显示不闪烁。 电路分析 电子显微镜的保护电路主要是用于在某种原因引起高压箱电流异常增大时，切断高压发生回路和灯丝回路的电源，起安全保护的作用。 此电路上端点的电压上升到3．5V时，由IC1的4、5、2脚组成的起滞后作用的比较器的2脚输出“L Symptom Beam current exceeds 180μA and the bias display does not flicker. Circuit Analysis The protection circuit of the electron microscope is mainly used to cut off the power supply of the high-voltage generating circuit and the filament circuit when the cause of the abnormal increase in the current of the high-voltage box is caused by a certain cause, and plays a role of safety protection. When the voltage at the end of this circuit rises to 3.5V, the 2-pin output of the comparator composed of pins 4, 5, and 2 of IC1 that acts as a hysteresis "L