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All the functions of this lcd tv were good except the contrast and brightness controls. When I decreased the contrast and brightness to 50 %, after few minutes it automatically shot up again to 100%. My first suspect was the corrupted program file of EEPROM IC . Since I do not have the original programs I tried to check on the voltages to see if the voltages stable or not.
I measured the output voltages from the power supply and found two voltages were good (13v and 12 v). But the 5 volt line seems to be unstable and fluctuated. After that I saw an electrolytic capacitor that was bulged located along the 5 volt line.
The cap value was 2200 micro farad @ 10 volt 105 C and when tested with my capacitance meter it showed only 32 micro farad. The capacitance value was way out. I checked the same capacitor again with my ESR meter and it showed 2 ESR ohm. By right it should have about 0.02 ESR ohm. After a new replacement was done the control functions of the contrast and brightness of the TV was back to normal again.
Note: I changed the bad cap with new one. 2200micro @ 16volt 105 c and this works with no problem.
Conclusion : An exact and stable voltage is a must for the supply of microcontroller IC.
Beh from Iran
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