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一台飞利浦20CT6050彩电图像正常,无伴音且调谐选台彩条指示线不消失。根据电路原理分析,认为同时出现无伴音且调谐指示线不消失的故障与行扫描电路有关。首先测量TDA2577(13)脚电压,发现有信号时为4.4V,无信号时为11.33V(正常有信号时1.35V,无信号时为11.26V)。显然(13)脚电压在有信号时升高了3.05V。检查(13)脚外围电路3879、3875、3877都正常。TDA2577(13)、(18)脚外接电阻3879、3880、3875、3877、电容2880与内电路构成功能自动转换电路。在选通门电路的控制下,从(13)脚输出识别信号,经电阻3880、3875分别送至选台调谐彩条指示电路LM339的⑧脚和中放电路晶体管7165的基极,以实现彩条指示和静噪控制功能。由于TDA2577(13)脚电压升高,导致图像中频电路中晶体管7165基极电压升
A Philips 20CT6050 color TV images normal, no sound and tuning station color bar indicator line does not disappear. According to the analysis of circuit theory, it is considered that the failure that accompanies no sound and the tuning indication line disappears at the same time is related to the line scanning circuit. First, measure the voltage of TDA2577 (13) pin and find 4.4V when there is a signal and 11.33V when there is no signal (1.35V when there is a normal signal and 11.26V when there is no signal). Obviously (13) pin voltage increased 3.05V when there is a signal. Check (13) foot peripheral circuits 3879,3875,3877 are normal. TDA2577 (13), (18) feet external resistors 3879,3880,3875,3877, capacitor 2880 and the internal circuit constitutes a function of automatic conversion circuit. Under the control of the gate circuit, from (13) feet identification signal output, respectively, through the resistance 3880,3875 were sent to the election tuning color bar indicating circuit LM339 pin and the base of the discharge transistor 7165 in order to achieve color Bar indication and squelch control functions. As TDA2577 (13) pin voltage increases, leading to the image IF circuit transistor 7165 base voltage rise