Replacing Working Components In Switch Mode Power Supply
The OLAN 22″LCD TV came in with the complaint of no power symptom. Once the cover was removed I saw four circuit boards:
- Inverter Board
- Power Supply Board
- Main board
- USB Port that shared with the AC incoming board
The first thing to check was obviously is the main fuse and it was open circuit. With visual inspection I saw the main filter capacitor already bulged as seen from the photo below:
Checking on the power FET on board found it to be shorted. I proceeded to check on other components in the power primary side and found the current sense resistor was open circuit too.
As a precaution measure, I also replaced three working components ie; Optoisolator IC, TL431 IC and a filter capacitor. The reason I replaced the working components is because from experience, these component although are good at time of testing, it can go bad later. Why not replace it than to worry it will come back later for repair? A repeated call by customer will always be a non-profit repair. Once the components were replaced and powered On, the LCD TV came back to life.
Conclusion- You need lots of testing components skills to be able to understand the characteristics of electronic components. Some you can check on board, some you need to test it off board and some will tend to breakdown when under full load. If you would like to be good in checking electronic component, I can recommend Jestine’s Ebook. He uses his methods to accurately check on many electronics components with the help of few different meters.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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