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Unexpected Shorted Parts In LG LED TV
Customer sent to me this 22 inch LG LED TV with the complaint of no power. The model of this TV is 22LD310. I have connected the AC power to the TV and indeed, it was no power. The reason I test the TV again is because sometimes the problem could be different of what the customer actually complaint at.
For example, when you turn on the TV there is power LED, after few seconds later the power LED went off. This symptom is totally different from a no power fault.
Once the metal cover was removed I can access to the connector to check on the DC output voltage. Since the main fuse did not blow, so to confirm it is actually power supply fault or mainboard fault is to measure the DC output voltage. The result was zero volt and this indicated it was the power supply fault.
The next step is to check on the components in the power primary side. I found one zener diode component was shorted and others corresponding components seems to be good. I thought I have repaired the set by replacing the zener diode but the problem was still the same. The below photo is the result of a shorted zener diode:
I did not give up and continued to check on other components such as secondary side output diodes and Optoisolator IC.
You wouldn’t believe if I told you the Optoisolator IC was short circuited in the phototransistor side.
A new replacement part of PC817B (4 leads) cured the fault. Below are the photos of a lighted LED and a working TV set.
Conclusion- If you want to learn how to test components to perform the electronics repair work you can get Jestine Basic Electronics Repair ebook Here. If you want to be a professional in switch mode power supplies repair then you need to check out his another ebook HERE. Ok see you in the next article.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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