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例一:接收电视节目时,图像、伴音均正常,但图像顶部出现几根回扫线。分析与检修:此回扫线的产生是因场扫描逆程时间延长,引起场逆程脉冲幅度减小所致。测IC的⑦脚正常,故怀疑场输出级发生故障。如附图所示,电容C_(412)为场输出级电路的自举电容。如果此电容损坏或失效,Q_(402)基极电压不能随场输出中点电压升高,将使场扫描正程的前半部分输出幅
Example 1: When receiving a TV program, images and sound are normal, but there are several retract lines at the top of the image. Analysis and Overhaul: The generation of this flyback line is due to the prolonged vertical sweep of the field scan, resulting in the decrease of the amplitude of the field reverse pulse. Test ⑦ feet normal IC, it is suspected field output stage failure. As shown in the figure, capacitor C_ (412) is the bootstrap capacitor of the field output stage circuit. If this capacitor is damaged or fails, the Q_ (402) base voltage can not increase with the midpoint voltage of the field output and will cause the first half of the field scan range output amplitude