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[例18]故障现象:VGA状态下有声音输出。分析与检修:首先通电测试,在VGA状态下有音频输出,而正常机器在VGA状态下应该是没有音频输出的。根据信号流程图,我们知道,声音的选择是通过U100的輰訛輪和輱訛輪脚输出控制信号,控制Q108和Q109的工作状态,然后控制U104的选择信号。测量U104的输入控制⑨脚和⑩脚,发现⑨脚是高
[Example 18] Symptom: There is sound output in VGA status. Analysis and Maintenance: First of all, the power test, there is audio output in the VGA state, while the normal machine in the VGA state should be no audio output. According to the signal flow chart, we know that the sound is selected by the U100 error signal and the error output wheel caster control signal to control the work of Q108 and Q109, and then control the selection signal U104. Measurement U104 input control ⑨ feet and ⑩ feet and found ⑨ feet is high