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实例18 一台珊瑚D47C—9型彩电,在正常收看1h(小时)后,出现无图像、无光栅、有伴音故障。关机10min(分钟)后再开机,电视机能收看到电视节目,但在10s(秒钟)内图像光栅消失,故障重复再现。分析与检修:从该机有声无光故障现象反复出现,初步判断是保护电路出现故障。此类机型保护电路由集成块IC801(TA7698AP)的(24)、(30)、(33)脚内部电路及外围元件组成,含有阳极高压过压、束电流过流及场输出电容短路三个保护功能,其中(30)脚的直流电压是保护电路是否动作的参考点。正常工作时,U_(30)=0V,当U_(30)=1.5V时,表明保护电路动作,此时,(30)脚内的高
Example 18 A coral D47C-9 color TV, after normal viewing 1h (hours), there is no image, no grating, with sound failure. Shut down 10min (minutes) and then boot, the TV can watch TV shows, but in 10s (seconds) disappears image raster, repeat the fault. Analysis and Maintenance: From the machine soundless recurring phenomenon, the initial judge is the protection circuit failure. The protection circuit of this type is composed of internal circuits (24), (30) and (33) of the integrated circuit IC801 (TA7698AP) and external components, including three types of anode high voltage overvoltage, overcurrent of the beam current and short circuit of the field output capacitor Protection function, in which (30) DC voltage is the protection circuit is the reference point of action. Normal operation, U_ (30) = 0V, when U_ (30) = 1.5V, that the protection circuit action, this time, (30) feet high