描述
在PC2输出端并接10KΩ电阻,输出电压回落,说明PC2输出侧稳压电路正常,故障在PC2本身以及输入侧电路。在R7上并联500Ω电阻,输出电压有明显回落,说明光耦PC2良好,故障在PC3低效或者PC3外接电阻元件变值,反之,为PC2不良。供电电压过低,有三个故障可能:负载过重,使输出电压下降;稳压回路元件不良,导致电压反馈信号过大;开关管低效,使得开关变压器储能不足
。将供电支路的负载电路逐一排除,判断是否由于负载过重引起的电压回落,如切断某路供电后回复正常值,说明开关电源本身正常,检查负载电路,若输出电压低则检查稳压回路。检查稳压回路的电阻R5~R10,无变值现象;逐一代换PC2,PC3,若正常,说明代换原件低效。代换PC2,PC3无效,故障可能为开关管低效,或者UC3844内部输出电路低效,代换优质开关管或者UC3844芯片。
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