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例2.故障现象:通电后“三无”。分析检修:实测开关电源+B输出电压偏低,测开关管V823(2SC4706)集电极电压为300V正常,而+B电压仅75V左右。分析造成+B电压偏低的原因主要有:(1)稳压控制电路异常;(2)待机控制电路不良;(3)过压、过流保护控制电路故障;(4)低压限制控制电路异常;(5)由N829、V839、V840等组成的恒流驱动电路异常。根据测量结果,首先断开待机控制管V828(2SC2230)
Example 2. Symptom: After the power “three no.” Analysis and Maintenance: Measured switching power supply + B output voltage is low, measuring switch tube V823 (2SC4706) collector voltage is 300V normal, and + B voltage is only about 75V. Analysis of the causes of low voltage + B are: (1) regulator control circuit abnormalities; (2) standby control circuit is poor; (3) overvoltage and overcurrent protection control circuit failure; (4) low voltage limit control circuit is abnormal ; (5) by N829, V839, V840 and other components of the constant current drive circuit abnormalities. According to the measurement results, first disconnect the standby control tube V828 (2SC2230)