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当无台或有台时,屏幕总会出现一片雪花噪点,看起来很不舒服,下面介绍一个简易蓝色背景电路,熊猫3625型彩电采用飞利浦机芯,CPU采用PCA84C640。工作原理:PCA84C640芯片的(29)脚为电台识别信号输入端,当有台时电压为4.5V左右(高电平),当无台时为0.5V左右(低电平),(27)脚是场同步信号。当(29)脚为低电平时BG1截止,BG2导通,蓝色视放管发射极电压下降,使电视屏幕出现蓝色背景,但屏幕上还将
When there is no Taiwan or Taiwan, the screen will always appear a piece of snow noise, looks very uncomfortable, here is a simple blue background circuit, Panda 3625 color TV with Philips movement, CPU using PCA84C640. How it works: PCA84C640 chip (29) feet for the radio identification signal input, when the station when the voltage is about 4.5V (high level), when there is no station when about 0.5V (low), (27) Is the field sync signal. When (29) pin is low when BG1 ends, BG2 turns on, the blue tube emitter voltage drops, the TV screen appears blue, but the screen will