出故障时字符消失及所有操作失效,说明CPU工作不正常。该机伺服主板采用TE-802C主板。测其CPU(KS56C820-69A)供电端{46}脚电压,正常工作时为5V,故障出现后降为1V。5V供电电路见附图。故障时测Q306的c极电压为1V,e极为1.5V,IC1(7808)输入端电压为12V。经仔细检查发现其输出端{3}脚引脚剪得过短无法接触。更换一新IC后,故障排除。 |
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