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故障现象:一台长虹C2169彩电,出现图像不停地上下抖动,在抖动的同时,图像轻微地伸缩,亮度、彩色、伴音均正常。分析检修:场抖一般与场频有关,一个原因是场振荡频率有异常,与全电视信号的场同步脉冲的频率略偏低,不能被同步脉冲完全锁定;另一个原因是全电视信号的场同步脉冲不正确,不能与本机场频50Hz保持一致而造成抖动。首先查TA7698第(28)、(29)脚外接的定时元件及制武切换电路正常,再查TA7698第(36)脚到第(28)脚的同步脉冲积分电路,电容全部换尽亦无济于事;怀疑同步头被削减,查TA7698第(37)脚至第(40)脚的电路,也正常,最后
Symptoms: A Changhong C2169 color TV, appears constantly shaking up and down the image, shaking at the same time, the image slightly telescopic, brightness, color, sound are normal. Analysis and maintenance: Field jitter is generally related to the field frequency. One reason is that the field oscillation frequency is abnormal. The frequency of the field sync pulse with the full-TV signal is slightly lower than that of the full-field sync pulse and can not be completely locked by the sync pulse. Another reason is that the field of the full-TV signal Sync pulse is not correct, can not be consistent with the airport frequency 50Hz caused jitter. First check the TA7698 (28), (29) external timing components and switching weapons Wu normal, and then check the TA7698 (36) feet to (28) feet synchronous pulse integration circuit, all the capacitors are also exhausted; Suspect sync head is cut, check the TA7698 foot (37) to the foot of the circuit (40) is normal, and finally