上门维修收到其他维修同行的一台康佳LC32CS11,二次开机后无光无声。打开机壳,测dianyuan电源板5V正常,12V 24V无输出,用1K电阻跨于5V与开待机控制脚之间,测CF901 450V/150Uf两端为308V,判断【故障】在PFC电路。测PFC芯片供电脚8脚为0v,该脚受控于QB902B极,只有当光耦N950 3 , 4脚导通,QB902(PNP型)b极电压下降,c极才会有电压输出至PFC芯片8脚。测光耦N950 1,2脚间压降为0.7V, 3,4脚间压降为14.3V(应为0V),判断该光耦N950损坏,更换后开机,12V , 24V输出正常,灯管点亮,【故障】排除! |
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