Unexpected PC817 Opto IC Problem In Marchsal LCD TV
I received this LCD TV and claim of owner was when TV is not warm TV work as normal but after a while when TV getting warmer the picture start to blink. I tested it out and it was true.
First I thought that the problem must be from backlight, ccfl and/ or transformers inverter IC.
I checked them all and try to bring out the inverter IC from protection mode by grounding the sense pin of inverter IC to ground (when each of the ccfl or transformers are malfunctioning, the inverter IC is going into protection mode and the IC will turn off the voltages to backlights in order to stop more damages to the TV )
But after shorted the inverter IC to ground, the problem still exist! I replaced the driver IC and also all bad electrolytes like 24 volts, but still problem is not solved! By experience I knew that this could be from the bad intermittent ICs in power supply. The IC does not show any problem when is not warm but when getting warmer start to on/off.
But I found it by this old trick. When TV is not warm by getting close the tip of a hot soldering iron to each of the suspect ICs in power supply you can find the bad IC. This time I found intermittent bad IC it was Opto- coupler PC 817 in location 120 on the board when I getting close the hot tip of soldering iron to the IC and the picture start to blink.
By replacing the IC the TV return to normal service and one more electronic machine rescued.
This article was prepared for you by Mr Beh from Iran.
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