故障现象:手机不振铃。分析检修:与故障有关电路如附图所示。由原理可知,手机振铃是通过主机外线端L1、L2输入的铃流信号经L2、L3抗干扰电感,C1隔直电容,R2、R3限流电阻,ZD1抗干扰二极管加至IC8,使IC8内的发光管点亮,光敏管导通,低电平振铃检测信号经R5送至微处理器UC1775第⒀脚,经内部处理后输出数据 Symptom: phone does not ring. Analysis and Maintenance: The circuit related to the fault is shown in the attached figure. It can be seen from the principle that the ringing of the handset is performed by the L2, L3 anti-jamming inductance, C1 blocking capacitor, R2, R3 current limiting resistor and ZD1 anti-interference diode added to the ringing signal input through the external terminals L1, L2 of the host computer, The LED light, light-sensitive tube conduction, low-level ringing detection signal sent to the microprocessor by the fifth foot UC1775 foot, the internal output data after processing