From the failure phenomenon analysis, which is a temperature related failure. After the failure of the image details can not be resolved, the high frequency components of the video signal is lost. Since the image synchronization state is always good, therefore, the inspection focus should be placed on the video part of the circuit.

General TV video portion of the circuit is relatively simple, from put the video signal output circuit enters the decoding IC for color decoding and brightness signal amplification, to output depending on the final directly promote the imaging tube cathode. But the machine uses Panasonic m18m movement, the multifunctional machine, and the use of the various video processing technology. Therefore, the video signal process twists and turns, is very complex.

Put the video signal circuit IC101 (M52760SP) output by IC201 M52317SP TV mode selection of, rushed to the AV / TV conversion circuit IC3001 AN5858K, IC3001 select the desired video signal and by {21} pin output, rushed to the Y / C separation circuit separation excellent signal (c) and the luminance signal (y), back again IC3001{20}, {19} feet. By IC3001{17} feet in the output signal Y, {15} foot output C signal. The Y signal in turn into the image of artificial intelligence (A1) circuit, horizontal sharpness enhancement circuit for processing, and then sent to the color processing circuit IC601 (ta1215an).

By C signal IC3001{15} pin outputs, PAL4.43MHz chrominance signal by the foot of the IC601{49} into, the demodulation of IC601 a R - y, B-Y signal, respectively by {40}, {41} feet in the output and sent to 1H delay line IC603 TA8772AN {27}, {26} feet. IC603 and after 1H delay r - y, B - Y signal respectively from {30}, {29} output pin, return to the foot of IC601{37}, {38}, then within the IC601 by color difference matrix circuit to produce a G Y signal.

Image artificial intelligent circuit and horizontal sharpness enhancement circuit for processing a luminance signal input by the IC601{60} feet, in the interior of the IC601 for further processing of evacuation to the IC's internal color matrix circuit, and R - y, g y, B-Y color difference signal together to demodulate R, G and B color signals, and then by the {16}, {17}, {18} pin output to the IC3401 TA8889AP {1}, {3}, {6} feet. IC3401 is the I2C bus control of white balance adjustment circuit, the adjusted R, G, B signal by the {16}, {14}, {12} output, send to the last stage depending on the circuit IC351 (tda6103q) {1}, {2}, {3} feet. After amplification by {9}, {8}, {7} feet in the output to the imaging tube cathode.

From this point of view, the video signal of the machine through the path more, it is easy to determine the loss of the high frequency component of the video signal accurately. However, it should be noted that this fault with image quality becomes poor and brightness decline phenomenon, and brightness changes, will some point appeared in the DC potential changes, from the lookup caused tube brightness decline reason of, may be able to find out fault reason.

According to the above analysis, the 9V and 12V voltage of the small signal processing circuit of the whole machine is checked, and the failure of the signal processing circuit is not changed.

Then measured IC351 R, G, B output end {7}, {8}, {9} pin voltage, found after a failure in the voltage from the normal value about 160V were up to 202V, 197V, 197V. Because the IC351{5} pin is a reference voltage, the change of the end voltage will affect the R, G, B output of the DC voltage at the same time. Therefore, the monitoring of the IC351{5} pin voltage is not changed, the next step is to detect the DC voltage of the IC351 input terminal. Because of its {1}, {2}, IC3401{16} and {3}, {14}, {12}, pin for the DC coupling, to shorten the maintenance time, direct measurement of IC3401{12}, {14}, {16} pin voltage. Just when the phone is switched on, the IC3401 the tripod DC voltage respectively 2.67v, 2.85V, 3.02V. With the boot time decreased to 2.10V, 2.17V, 2.31v, its input end {1}, {3}, {6} feet DC voltage is respectively from the 2.10V, 2.23V, 2.39V fell 1.70 V (SCE). And 1.69V, 1.69V. Because of IC3401{1}, {3}, {6} feet and IC601{16}, {17}, {18} feet through and DC voltage variation IC601 input end of the may also affect the output DC voltage changes, therefore, measuring IC601 RY, B-Y input end {37}, {38} pin voltage, stable without change. As can be seen from the figure, and IC601 IC603 no DC coupling. Therefore, the pin is DC voltage will influence each other, but consider to IC601 input signal amplitude changes would also affect the output DC voltage changes, so the signal wave form of oscilloscope monitoring IC601{37}, {38} feet, to appear before and after the fault amplitude without significant changes.

At this point, the basic judgment of the fault in the IC601 and its peripheral part, because of the failure and temperature changes are closely related, it will focus on the IC itself. IC601 internal function, the price is expensive, in order to ensure the accuracy of the judgment, the trial cooling method to further judge. Fault to be complete, with alcohol cotton ball on IC601 wipe help cool. After a moment image recovery normal, stop for a period of time after cooling and the failure to reproduce, repeated several times. Determine the IC601 bad, replace the troubleshooting.