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例1.故障现象:红梅WJD—18型黑白机,光栅、图像均正常,但稍开一点儿音量旋钮,音量就最大,无法正常使用。分析与检修:如图1。该机伴音通道采用集成块μPC1353,第(14)脚为音量控制脚,外接4.7kΩ音量电位器进行直流电位控制,此直流电位是由8V电压经20kΩ、4.7kΩ、390kΩ三只串联电阻进行分压后,由音量电位器滑动触头取得的。检测该电位器,发现其接地下端与其它两端有开路现象,拆开电位器,发现内部碳
Example 1. Symptom: Hongmei WJD-18-type black and white machine, grating, the image is normal, but a little bit more volume knob, the volume is the maximum, can not be used normally. Analysis and maintenance: Figure 1. The sound channel of this machine adopts the integrated block μPC1353, the fourteenth leg is a volume control leg, and the external 4.7kΩ volume potentiometer is used for the DC potential control. The DC potential is divided by 8V voltages through three series resistances of 20kΩ, 4.7kΩ and 390kΩ After pressure, obtained by the volume potentiometer sliding contact. Detection of the potentiometer and found that the bottom of the ground with the other ends open the phenomenon, open the potentiometer and found that the internal carbon