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故障现象:光栅正常,无图像,有失控的噪声。检修过程:光栅正常,有噪声,说明后级电路工作正常。前级电路未正常工作。全机是在微处理器MN15287KWEC控制下工作。首先查该芯片是否有工作电源,其①脚为地,(52)脚为电源正端。测量(52)脚无5V工作电压。查前端电源供电端,其工作电压是由开关电源中T902、V908所组成的副开关电源而来,经VD910整流,三端稳压器V904(7805)输出5V,经XS602插件进入主板。查V904无5V电压,而V904输出端有10V电压,说明VD904有问题,焊下测量VD904内部断路。换新后,开机出现“三无”现象。说明整个电路在微
Symptoms: grating normal, no images, there is no control of noise. Maintenance process: grating normal, noisy, indicating that the circuit is working properly. Pre-circuit is not working properly. The whole machine is under the control of the microprocessor MN15287KWEC. First check whether the chip has a working power supply, its ① feet to ground, (52) feet for the positive power supply. Measurement (52) feet without 5V working voltage. Check the front-end power supply side, the operating voltage from the switching power supply T902, V908 formed by the sub-switching power supply, the VD910 rectifier, three-terminal regulator V904 (7805) output 5V, XS602 plug into the motherboard. Check V904 no 5V voltage, and V904 output 10V voltage, indicating a problem VD904, Weld test VD904 internal circuit. After the change, the boot appears “three noes” phenomenon. Shows the entire circuit in the micro