故障现象:该机最初故障表现为水平一条亮线,经他人修理后,不但未修复,反而扩大了故障,后期表现为“三无”。分析检修:首先检查保险丝F501已熔断,更换F501后,开机F501立即被熔断,说明机内电流过大,电路存在短路性故障。该机采用自激式脉冲变压器耦合型开关电源。220V电压经VD503～VD506桥式整流、L503、C507、C518滤波后得到脉冲直流电压加至开关变压器T511的初级绕组,再经开关管V513与地构成回路。V512为开关控制管,其作用是控制V513的导通时间。 Symptoms: The initial failure of the aircraft showed a level of a bright line, after being repaired by others, not only failed to repair, but expanded the fault, the latter showed “three noes.” Analysis and maintenance: First check the fuse F501 has blown, replace the F501, the boot F501 immediately blown, indicating the machine current is too large, the circuit short-circuit fault. The machine uses a self-excited pulse transformer coupled switching power supply. 220V voltage by VD503 ~ VD506 bridge rectifier, L503, C507, C518 filtered pulse DC voltage is applied to the primary winding of the switching transformer T511, and then formed by the switch V513 loop. V512 for the switch control tube, its role is to control the V513 on-time.