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例1 故障现象:该机无来电振铃声,无拨号音,不能拨打电话,但主机与手机间能正常通话。分析检修:根据故障现象分析,主机与手机收发电路均正常,故障应在市话线路与电话机话音电路,相关电路原理如图1所示。由图可知,外线接至极性转换器 D1～D4,话音及拨号经由
Example 1 Symptom: The machine has no ringing tone, no dial tone, can not make calls, but the host and the phone can talk normally. Analysis and maintenance: According to the analysis of the fault phenomenon, the host and the phone transceiver circuit are normal, the fault should be in the local telephone lines and telephone voice circuits, the circuit shown in Figure 1. It can be seen from the figure that the outside line is connected to the polarity converters D1 to D4, and the voice and dialing are via