用500型三用表直流电压500v、50v、10V挡,测整机高压供电电路,C4对地+305V电压,正常。测低压供电电路C92对地+18V电压。正常。测C91对地+5v电压,正常。测比较器(U2B)(1)脚输出端对地+0.2v电压(正常为+4.9V),测(U2B)(7)脚同相输入端对地+3.4V电压,偏低(正常为+4V),比较器(U2B)已翻转由高电平变为低电平。将三用表拨至RxlOk挡,检测发现电阻R16(470kΩ/lW)变值至510kΩ,更换电阻R16后整机恢复正常。 |
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