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故障现象 一台明科MK-757型CD唱机,不能启动工作,也无显示。 分析与检修 从该机的电路结构来看,当插上电源插头,接通220VAC电压时,AC电压加至机内电源变压器初级,由该变压器降压,再经整流、滤波、稳压电路稳压得到的12VDC电压加至启动电路中。 启动电路主要由双D触发器及驱动开关管VT9、小型继电器KA等组成(相关电路如附图所示),其作用是控制继电
Symptom A Ming Ke MK-757 CD player, can not start working, there is no display. Analysis and maintenance From the machine’s circuit structure, when plugged in, connected to 220VAC voltage, AC voltage added to the primary power transformer, the transformer step-down, and then rectified, filtered, voltage regulator circuit The resulting voltage of 12VDC is applied to the start-up circuit. Startup circuit is mainly composed of double D flip-flop and drive switch VT9, KA and other small relay (related circuit shown in the figure), its role is to control the relay