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故障现象分机不能打外线电话，其他功能正常。分析检修检查主机接收电路工作良好，说明主机控制电路有故障（见图1）。根据主机电路分析，当分机按下通话键时，主机接收其导频信号送入控制集成电路A3的10脚，A3的2脚输出高电平，经电阻器R112耦合使晶体管V13导通，搞机继电器K
Symptom Extensions can not make outside calls, other functions are normal. Analysis and inspection of host receiving circuit works well, indicating that the host control circuit is faulty (see Figure 1). According to the host circuit analysis, when the extension press the call key, the host receives its pilot signal into the control integrated circuit A3 10 feet, A3’s 2 feet output high, the transistor R1 is turned on by the resistor R112 coupling Machine Relay K