From the analysis of the phenomenon of failure, indicating circuit CPU and audio amplifier circuit is normal, fault most likely audio processing circuits.
This machine uses IC512 (TDA8844) in images, sound, and small-signal processing, the field scan, color decoding, and brightness, color separation, and so on. As drawings by shows, video full TV signal from IC512{6} feet output, by C520, and (62pF), and R514 (1k ω) sent to sound MF more standard demodulation IC HTC2 (LG9842) {2} feet, by internal standard conversion switch demodulation Hou of second sound MF signal by {4} feet into IC512{1} feet, sound MF signal by IC512 internal with pass filtering, and pre zoom and the volume switch control Hou, from its {15} feet output to sound amplifier circuit. Meanwhile, HTC2 under CPU control, in the case of different standards, HTC2{8}, {9} feet at low and high level changes when receiving DK (China) {8} when TV mode PIN is 0V, {9} feet 1. 4V。


Control keys screen displays "DK" characters, the measured voltage is 0V, {9} HTC2{8} feet foot 1. 4V, the correct CPU-controlled HTC2, HTC2{4} no output is the internal damage caused by foot. LG9842 is expensive and difficult to repurchase in a timely manner, according to circuit theory analysis of the machine, as shown in fig disconnect HTC2{2}, {4} feet, the other three Terminal LT6. 5M ceramic filter circuit test machine, sound normal, still in use for more than a year, the effect is very good.