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十、图像中频电路工作原理与故障分析检修 1.图像中频电路的构成、功能及原理分析 TA两片机彩色电视机图像中频电路,大多由一级预中放、声表面滤波器和TA7680AP(CD7680CP)内部分电路与外围元件构成。其基本电路结构和工作原理均大同小异。现以有一定代表性的北京牌8316—2型彩色电视机的图像中频电路(如图29所示)为例,图像中频电路的主要功能与工作原理分析如下: 图像中频电路的主要功能,是将高频头送来的图像中频信号(IF)进行放大,然后经视频检波电路获得彩色全电视信号(F、B、A、S)和第二伴音中频SIF(6.5MHz)信号。为使高频头内本振频率能始终保持在允许偏差范围内(±50kHz以内),图像中频电路中均设有AFT(自动频率微调)电路。并为保证中放输出视频
Ten, the image IF circuit working principle and fault analysis and maintenance 1. Image IF circuit structure, function and principle analysis TA two-chip color TV image IF circuit, mostly by a pre-release, SAW filter and TA7680AP (CD7680CP ) Internal circuit and peripheral components. The basic circuit structure and working principle are the same. A typical representative of the Beijing brand 8316-2 color TV image IF circuit (Figure 29) as an example, the main function of the image IF circuit and the working principle is as follows: The main function of the image IF circuit is The IF signal sent from the tuner is amplified, and then the full-color TV signal (F, B, A, S) and the second audio IF signal (6.5MHz) are obtained by the video detection circuit. In order to keep the local oscillator frequency within the allowable deviation (± 50kHz), AFT (Automatic Frequency Trimming) circuit is installed in the IF circuit. And in order to ensure the release of video