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[例5]故障现象:不开机。分析与检修:首先开机测试,发现机器没有开机,一直处于待机状态。测试电源只有5VSTB的电压,而主电源没有12V电压。首先通过更换电源板排除了电源板的问题,问题在主板。根据电源的逻辑关系图我们知道,在待机时,电源板提供5VSTB(待机)电压,供给U110产生2.5V电压,供给U112产生3.3V电压,这些电压未提供给U100和U103、U102,使机器处
[Example 5] Symptom: do not boot. Analysis and Maintenance: First boot test, found that the machine does not boot, has been in standby. Test power only 5VSTB voltage, while the main power supply without 12V voltage. First of all by replacing the power board to exclude the power board problem, the problem on the motherboard. According to the logic diagram of the power supply, we know that in the standby mode, the power supply board provides 5VSTB (standby) voltage, supplying U110 to generate 2.5V voltage and supplying U112 to generate 3.3V voltage. These voltages are not provided to U100 and U103 and U102,