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例1 故障现象:主机一频道发射失效。分析与检修:分析该机原理,电路如图1所示。发射基频在主振级Q14产生,共有三个发射基频,分别由Q14、C68、C71及晶体X4、X5、X6等组成的晶体振荡器产生。主振级Q14产生的发射基频为12.6917MHz,在Q16、Q17、Q18上可分别产生38.0751MHz、76.15MHz、152.3MHz的高频FM信号。该高频FM载波信号,经C95耦合,被送入由Q19、Q20、Q21等电路组成的三级高频发射电路。其中Q19、Q20分别为缓冲放大级及推动级,产生推动Q21所需的足够的激励信号,
Example 1 Symptom: host a channel lapsed. Analysis and Maintenance: Analysis of the machine principle, the circuit shown in Figure 1. The fundamental frequency of the transmission is generated at the main vibration level Q14. There are three fundamental frequencies of emission, which are respectively generated by crystal oscillators consisting of Q14, C68, C71 and crystals X4, X5, X6. The fundamental frequency of transmission generated by the main vibration level Q14 is 12.6917MHz, and the high frequency FM signals of 38.0751MHz, 76.15MHz and 152.3MHz can be generated respectively on Q16, Q17 and Q18. The high frequency FM carrier signal, coupled by C95, is fed into a three-stage high-frequency transmitting circuit consisting of Q19, Q20, Q21 and other circuits. Which Q19, Q20, respectively, for the buffer amplifier stage and the promotion level, to produce enough to stimulate the Q21 excitation signal,