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故障现象:副机不能呼叫主机,但主机能呼叫副机,通话、拨号等其他功能均正常。分析与检修:副机呼叫主机电路由主机和副机中的相关电路共同组成。首先检查到机中的相关电路,没有发现异常,说明故障发生在主机中的相关电路,主机中的相关电路如图1所示。副机呼叫主机时,副机发射的已调呼叫信号,由主机中的天线接收、三极管放大.并经集成电路MC3361内混频、鉴频、解调后,由MC3361的⑨脚输出,经R10、C41送入IC2 LM567单音译码集成电路的③脚,经IC2内部进行呼叫导频信号解调,使得IC2的⑧脚输出低电平。这一低电平分成两路:一路使三极管Q9导通,+8V电源电压经过Q9的c、e极加至话机电路中由Q105、Q106、Q119组成的低频放大器,为低频放大器提供工作电源;另一路经过D10加至逻辑集成电路IC6(TC4001)的⑥脚,TC4001为四个输入端或非门,④脚输出高电平,使得六反相器
Symptom: The slave can not call the host, but the host can call the slave, call, dial-up and other functions are normal. Analysis and Overhaul: Vice-host calling host circuit from the host and vice-related circuit together. First check the relevant circuit in the machine, did not find abnormal, indicating that the fault occurred in the host of the relevant circuit, the host of the circuit shown in Figure 1. Vice host calls the host, the auxiliary machine launched the call signal has been adjusted by the host antenna, the transistor amplification, and after the IC MC3361 mixing, frequency identification, demodulation, by the ⑨ pin MC3361 output, the R10 , C41 into IC2 LM567 single tone decoding integrated circuit ③ feet, by IC2 internal call pilot signal demodulation, making IC2 ⑧ pin output low. The low level is divided into two: all the way to turn on the transistor Q9, +8 V power supply voltage after Q9 c, e pole added to the phone circuit consists of Q105, Q106, Q119 composed of low-frequency amplifier for the low-frequency amplifier to provide power; The other way after D10 added to the logic IC IC6 (TC4001) ⑥ feet, TC4001 for the four input NOR gate, ④ pin output high, making the six-inverter