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故障现象:在收看过程中出现一条水平亮线,但伴音始终正常。该类机易发生的故障就是一条水平亮线。应重点检测IC681(STA441C)场输出块及外围元件。根据STA441C内部框图可知,内包含两只二极管和两只NPN型硅三极管组成(如图1所示),与外围元件构成一个推挽功放电路。首先,用万用表测量IC681各脚电阻值,发现①～⑦脚数据均正常,而⑧～⑩脚内部三极管测量值有差异,但外围元件都良好。为了准确判断,将IC681⑧～⑩脚断开,测量发现该管呈开路状态。因为本机是一台老龄彩电,加上手头没有现成场输出块
Symptom: in the process of watching a horizontal bright line, but the sound is always normal. This type of machine prone to failure is a horizontal bright line. Should focus on testing IC681 (STA441C) field output block and peripheral components. According to STA441C internal block diagram shows, which contains two diodes and two NPN silicon transistors (as shown in Figure 1), with the external components constitute a push-pull amplifier circuit. First of all, with a multimeter to measure the resistance of the IC681 pin, found ① ~ ⑦ pin data are normal, and ⑧ ~ ⑩ pin internal transistor measurements are different, but the external components are good. In order to accurately determine the IC681 ⑧ ~ ⑩ feet off, the measurement showed that the tube was open. Because this machine is an old color TV, plus no ready-made output block on hand