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Shorted SMD Transistor In LED TV
The complaint of this 23″ LED TV was no display but there was power (the power LED light was on). The sound was good too except no display. However, the TV LED backlights were On -see the photo below.
This means that the internal LED TV driver board was working fine.
Once the cover was removed, I could see only two circuit boards i.e the main board and the backlight LED driver board.
I then checked on the mainboard voltages to the LED Backlight driver board and found that the three dc voltages of 3.3 volt, 5 volt and 12 volt were present. You need to check these pins when the dc power jack is connected and is on.
Next, I checked on the 5 volt dc line to the TV panel and found that it was only 1.44 volt instead of 5 volt. I knew this is the main cause of the TV no display problem.
I started to track from this 5 volt connector pin and found one suspicious SMD transistor where it received 5 volt but the output was only 1.44 volt.
I soldered out the SMD transistor and check it off board and true enough the transistor had a shorted leads where it showed 17 ohms. The ohms value should be high.
It is time to look for the spare part. I search from the junk board and found the right SMD transistor and soldered it-see the photos below:
After putting in the good SMD transistor and powered On, the 5 volt came back.
You can see the 5.09 volt reading from the meter in the photo below:
The best moment was able to see the TV display came back and the satisfaction is beyond description.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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