故障现象:每次开机3 min(分钟)便出现“自动关机”,约几秒钟后又自动开机,过半小时后又重复。分析与检修:起初以为是虚焊故障,开机检查电源及行电路都没有发现明显的虚焊现象,对其加焊了一遍,故障依旧。断开行电路接假负载,故障不变。又对开关电路进行仔细的检查。当故障出现时开关管 V513c极290V 电压,正常,b 极无电压,但当红表笔碰到 Symptoms: each boot 3 min (minutes) will appear “automatic shutdown”, about a few seconds and then automatically boot, half an hour later and repeat. Analysis and Maintenance: Initially thought to be Weld fault, check the power supply and the circuit did not find obvious Weld phenomenon, the welding again, the fault still. Disconnect the line circuit then leave the load, the same failure. Again on the switch circuit for careful examination. When the fault occurs when the switch V513c pole 290V voltage, normal, b very no voltage, but the red pen met