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故障现象:上门修理一台康佳T2518D型彩电,据用户反映,两月前开始出现彩色时有时无的现象,最近几天就根本无彩色了,但黑白图像正常。该机小信号处理电路采用LA7688N及附属电路,CPU为ST6368B,有关色度解码电路如图1所示。实际检修顺序: 1.普查N301(LA7688)相关引脚电压,发现除N301(17)脚(COLOR)异常(0.08V)外,其余各脚与图标基本相合。 2.断开R353,测量N301(17)脚电压仍为0.08V,而测断开的R353左端电压在0.9～1.8V之间变化(受CPU②脚调节),说明色度控制脚及外接元件无问
Symptom: Home to repair a Konka T2518D-type TV, according to the user, two months ago began to appear when the phenomenon of color sometimes, there is no color in recent days, but the black and white images are normal. The machine uses a small signal processing circuit LA7688N and ancillary circuitry, CPU ST6368B, the chroma decoding circuit shown in Figure 1. The actual inspection order: 1. Census related pin voltage of N301 (LA7688) and found that the pins and the icons are basically the same except that the color of the N301 (17) pin (COLOR) is abnormal (0.08V). 2. Disconnect R353 and measure the voltage of N301 (17) is still 0.08V, while the voltage of left end of R353 is about 0.9-1.8V (regulated by CPU ②), indicating that the color control pin and external components are not ask