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前些年生产的彩电,频道预选器大多是采用按键联动开关转换频道,电位器分压取得调谐电压的分立元件频道预选器。由于按键联动开关操作频繁,用不了多久就会出现机械接触不良故障,其现象是图像伴音不稳定,图像闪烁,对比度、清晰度不断变化,时常出现网纹,甚至出现不同步,伴音出现咔嚓噪声甚至时有时无。此时用手按一下联动开关一般会好一些,但过一会儿又出现类似现象。更换新的开关,由于市售开关质量较差,用不了多久又出现接触不良故障。用户对此十分头疼。笔者对电路进行了分析改进,用电子开关代替
A few years ago the production of color TV, channel preselection are mostly keyswitch switch channel, potentiometer partial pressure to obtain tuning voltage discrete component channel preselector. Due to the frequent operation of the key switch, mechanical failure can occur in a short time. The phenomenon is instability of the image sound, flickering of the image, constant change of contrast and sharpness, regular occurrence of anilox and even out-of-sync sound with clicking noise Sometimes even sometimes At this point by hand click the linkage switch will generally be better, but after a while there is a similar phenomenon. Replacement of the new switch, due to the poor quality of the commercially available switch, can not take long before it appears bad contact failure. The user is very headache. The author of the circuit analysis and improvement, with electronic switches instead