故障现象 一台莺歌C47-4型彩电黑白图像与伴音正常,但无彩色。 分析与检修 试用一只20k电阻跨接在IC301(TA7193AP)⑿脚与地之间,此时图像上出现了滚动的彩色干扰条纹,这说明无彩色故障是IC301内部的消色器关闭所致。消色器关闭故障大多发生在解码器电路上。故障原因有:(1)行逆程脉冲信号未输入到IC301④脚内的双稳态触发器上,使PAL开关失常。(2)色同步信号分离电路出故障,使色同步信号丢失。(3)VCO压控振荡器失常。为快速确定故障部位,首先用示波器观察IC301④脚(行逆程脉冲输入端)有1V_(p-p)幅度的行逆程信号波形,说明行逆程脉冲信号已输入到双稳态触发器上。 Symptoms A Yingge C47-4 color TV black and white images and sound normal, but no color. Analysis and Overhaul Try a 20k resistor across the 30 foot of the IC301 (TA7193AP) between ground and the picture shows a rolling colored interference fringe pattern, indicating that achromatic failure is caused by the closure of the internal color eraser in the IC301. Achromat shut down mostly occurs on the decoder circuit. The reason of the trouble is as follows: (1) Line reverse pulse signal is not input to bistable flip-flop in IC301 ④, so the PAL switch is abnormal. (2) color burst signal separation circuit failure, the color burst signal is lost. (3) VCO VCO abnormalities. In order to quickly determine the fault location, first observe the IC301 ④ foot-line (line reverse pulse input) line 1V_ (p-p) amplitude of the line inversion signal waveform oscilloscope, indicating the line back pulse signal has been input to the bistable flip-flop.