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3.维修案例[例1]故障现象:不开机。分析与检修:此机器是分公司的返修板。首先接入机架测试故障,发现指示灯亮,但是不开机。由于指示灯正常点亮,说明待机电路的5V待机电压正常。于是测试数字板插座P803的P14脚,发现没有高电平输出。进一步测试待机控制的Q803的基极为高电平,说明数字板的主解码芯片没有工作。检查数字板的待机电路,发现待机电路的U803的
3. Maintenance Case [Example 1] Symptom: do not boot. Analysis and Maintenance: This machine is a branch of the repair board. First access to the rack test failure, the indicator light, but does not boot. As the light is lit normally, indicating standby 5V standby voltage is normal. So test P143 P80 pin socket and found no high level output. The base of the Q803 for further test stand-by control is high, indicating that the main decode chip of the digital board did not work. Check the digital board’s standby circuit and find the standby circuit’s U803’s