故障现象SN－736型手机能正常向外打电话，但来话时无报铃。分析检修该机的振铃电路如图1所示。台机发出的高频振铃信号经接收通道处理后，由MC3357解图1振铃解调电路调，解调后的呼叫导频信号从9脚输出，经10、11脚内的选频放大器放大，由VD1、VD2整流，触发12脚由低电平变成 Symptom SN-736-type mobile phone can make a normal call, but no ring when the call. Analysis and maintenance of the machine ringing circuit shown in Figure 1. Taiwan machine issued by the high-frequency ringing signal processing by the receiving channel, the solution by the MC3357 Figure 1 ringing demodulation circuit, the demodulated call pilot signal output from the 9-pin, the 10, 10-pin amplifier within the frequency of amplification, Rectified by VD1, VD2, trigger 12 feet from low to become