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一般人以为300Ω馈线故障不外乎内部导线断路,其实不然,笔者曾遇到十几例较棘手的故障。现从中筛选出较有代表性的3例,供广大读者参考。例一,一台索尼20英寸遥控彩电,接有80多m 300Ω扁平馈线与室外接收天线相接,并装有天线放大器。一个多月来,逐渐出现灵敏度下降现象,呈进行性加重,后来发展到完全不能正常收看的程度。用户取另一台黑白电视机,接同一天线开机试看,故障依旧,遂从山头天线杆上取下天线放大器送来修理。经仔细检测,天线放大器的放大电路及电源电路均无异常,遂嘱用户回去仔细检查馈线。用户几经检查,未发现馈线有开路断线处,又携天线放大器前来修理。再次细测,天线放大器各点工作电压均正常,将其接入修理部的室外接收天线,通电开机试看,声图色彩俱佳,
Most people think that 300Ω feeder fault nothing more than internal wire breakage, it is not true, I have encountered more than a dozen cases more troublesome. Now select more representative of the 3 cases, for the majority of readers reference. Example One, a Sony 20-inch remote color TV, then received more than 80 m 300Ω flat feeders connected with the outdoor receiving antenna, and equipped with an antenna amplifier. More than a month, the phenomenon of gradual decline in sensitivity, was progressive increase, and later developed to completely unable to watch properly. Users take another black and white TV, the same antenna boot test, the fault still, then remove the antenna from the hill antenna amplifier sent to repair. After careful testing, antenna amplifier amplifier circuit and power supply circuit were normal, then asked the user to go back and carefully check the feeder. After several checks, the user did not find the feeder has open break, but also to bring the antenna amplifier to repair. Again carefully measured, the antenna amplifier operating voltage is normal at all points, access to the repair department of the outdoor receiving antenna, power boot try, sonography color superb color,