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四、判断高频头电路故障部位的方法 1.高频放大电路 (1)故障现象:在强信号下,能收到VH频段的微弱信号,但图像暗淡,背景上雪花状杂波点干扰严重;弱信号时无图无声,但有噪波点;在空频道上,光栅上的噪波点明显减少。这些现象表明故障在高频放大电路。之所以在强信号下能收到频率高端的电视信号,这是因为频道端信号频率较高,可以通过高放管极间耦合电容耦合到混频电路的缘故。 (2)高放级检测:在高频头中,高放级发生故障的机率比本振电路和混频电路高的多,并且以高放管(BG1)损坏最为常见,多以be结击穿或开路表现出来。
Fourth, to determine the frequency of the first part of the high-frequency circuit 1. High-frequency amplifier circuit (1) Symptom: In the strong signal, VH band can receive a weak signal, but the image is dim, the background of the snow-shaped clutter interference serious ; Weak signal no picture silent, but noisy point; empty channel, the grating on the noise point is significantly reduced. These phenomena indicate that the fault amplifier at high frequency. The reason why the high-frequency television signal can be received under a strong signal is because the channel end signal has a high frequency and can be coupled to the mixing circuit through a high-density coupling capacitor. (2) high-level detection: In the high-frequency head, the high-level discharge fault probability than the local oscillator circuit and mixer circuit is much higher, and to high-tube damage (BG1) is the most common, mostly beaten Wear or open the way shown.