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开机无光声,但电源指示灯亮。经查系R_(421)保险电阻开路,ZD_(403)(12/1W)稳压二极管击穿。造成这两个元件损坏的原因是VR_(901)(1kΩ)电源取样电仪器接触不良,使主电源输出电压瞬间升高,将ZD_(403)击穿后烧断R_(421)出现无光无声。由于VR_(901)接触不良的程度不同反映出故障现象也不相同:轻者,有时开机正常,工作一会儿自动关机,有时工作1天或几天后出现故障,无规律;重者则将ZD-(403)击穿。当出现上述现象之一时都应先更换VR_(403)。然后用7812稳压块代换击穿
Burn sound, but the power indicator light. The investigation by the R_ (421) insurance resistance open, ZD_ (403) (12 / 1W) Zener diode breakdown. The reason for the damage of these two components is that the power of VR_ (901) (1kΩ) is not good enough to contact the power sampling instrument, causing the instantaneous rise of the output voltage of the main power supply. After the breakdown of ZD_ (403), R_ (421) . Due to the different degree of bad contact VR_ (901) reflects the phenomenon is not the same: light, and sometimes boot normally, work for a while automatically shut down, sometimes 1 day or days after the failure, irregular; heavy ZZ- (403) breakdown. When one of the above phenomena should be replaced VR_ (403). Then replace the 7812 regulator block breakdown