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笔者接修了“三无”故障的两台昆仑牌S541-8A型彩电,出过差错,有过教训。现将有关教训提供给读者,以免重犯类似的错误。 该机电源原理图如附图所示。第一台故障机经查,保险丝完好。通电测量,Q506管射极无输出,C502(150μF/400V)两端有300伏电压,说明桥式整流滤波电路正常。测开关管Q503集电极和基极时,集电极电压为300伏,基极无电压(注:电源部分的“地”是“悬浮地”,以C501的负端作为“地”),再测取样放大管Q501和脉宽调整管Q504和Q502各脚电压均为零,但是,将表棒搭在C502的负端时为-300伏,到此发现R506(2.2Ω/2W)电阻已开路。
The author then repair the “three no” fault of two Kunlun brand S541-8A color TV, had made mistakes, had learned. The lesson is now available to the reader so as not to repeat a similar mistake. The machine power schematic as shown in the figure. The first failure of the machine check, the fuse intact. Power measurement, Q506 tube emitter no output, C502 (150μF / 400V) at both ends of the 300-volt voltage, indicating that the bridge rectifier filter circuit is normal. Measuring switch Q503 collector and base, the collector voltage of 300 volts, the base voltage (Note: the power part of the “ground” is “floating” to the negative side of C501 as “ground”), and then measured Sampling amplifier Q501 and pulse width control Q504 and Q502 each pin voltage is zero, but the watch stick to the negative end of C502 -300 volts, found that R506 (2.2Ω / 2W) resistance has been open.