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故障现象:关掉电源一段时间后,再一次开机不启动,整机不工作。故障分析:该机的开关电源板为台湾生产,型号为TPFB-45-6-M,有五组电压输出,分别是+5V/3.5A,+12V/0.5A,-12V/0.25A,+18V/1A。整机不工作,故障为开关电源不工作。检查维修:用万用表测开关电源各组直流电压均无输出,保险丝良好,判定开关电源没工作,测电源整流滤波输出端有310V直流电压,开关管良好,用示波器检查集成电路SG2842的⑥脚没有开关脉冲输出(注意,在用示波器测波形时,要用一个1∶1的隔离变压器接在开关电源前)。SC3842是应用很广的PWM脉宽调制型开关电源集成控制器,⑦脚为电压输入端,其启动电压范围为16～34V。当输入电压低于16V时,电路
Symptoms: turn off the power for some time, once again boot does not start, the machine does not work. Fault Analysis: The machine’s switching power supply board for the Taiwan production model TPFB-45-6-M, there are five voltage output, respectively, + 5V / 3.5A, + 12V / 0.5A, -12V / 18V / 1A. The whole machine does not work, the fault is switching power supply does not work. Check the maintenance: switch with a multimeter to measure the power supply of the DC voltage output of each group are not, the fuse is good, determine the switch power supply did not work, the power supply rectifier filter output 310V DC voltage, the switch is good, with an oscilloscope IC SG2042 Switching pulse output (Note that in the use of oscilloscope waveform, the use of a 1: 1 isolation transformer connected to the switching power supply before). SC3842 is a widely used PWM pulse width modulation switching power supply integrated controller, ⑦ pin for the voltage input, the starting voltage range of 16 ~ 34V. When the input voltage is lower than 16V, the circuit