LCD TV Backlights Overheating transformer on Samsung LN40B550K1F





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Published on May 3, 2013

I remember being told that the Cold Cathode Fluorescent Lamps on LCD TV's will draw more current as they begin to age due to a build up of carbon, After replacing a burnt out inverter transformer with a new one, I used my temperature probe on each of the 4 output transformers to see if my replacement transformer was operating at a higher temperature than the others, and i noticed it was. My first thought was there might have been an issue with the replacement transformer, so I tried swapping locations with one of the other transformers, but it still ran hot. My youtube friend Norcal715 suggested there might be an issue with AC ripple distorting the drive pulse going to the transformer due a bad electrolytic capacitor, but. when I examined the transformer inputs I noticed they all shared the same source, so this ruled out there being a bad capacitor on the input side, I also checked my ceramic capacitors on the outside and they all checked okay, and this led me to the conclusion that my Cold Cathode Fluorescent Lamps were starting to draw more current than they should due to a carbon build up from natural aging.
The TV I repaired is a Samsung Model LN40B550K1F. The inverter board number is a BN44-00264B. The transformer part number is QGAH02095.

For those who are interested here are some helpful books.
How to troubleshoot and repair Switch Mode Power supplies by Jestine Yong at http://davestv.jestinemichellepow.cli... This is a 271 page ebook packed with helpful information on how to troubleshoot switch mode power supplies which are found in many kinds of electronic equipment. I have many books and videos on this kind of power supply, but this is by far the best of my collection.
I created a video where I demonstrate some of the fundamentals of switching power supplies at this link. http://www.tvrepairinfo.com/switch-mo...
Testing electronic components and finding unknown resistor values by Jestine Yong. http://5d8388ioop4nfm862d1b0u7sbj.hop... This is a great book for beginners who want to learn more about testing electronic components.

How to repair LCD Computer Monitors by Jestine Yong at
Even though this book was about computer monitor repair I found most of the troubleshooting techniques he demonstrates also applied to LCD TV repair so I was glad to have read it. Much like the book on Switch Mode Power Supplies I found it was easy to understand.
Mikes TV case histories, This book has the combined case histories of 70 repair shops who have submitted their notes for Mikes book. It contains info on CRT, Plasma and Projection TVs. at http://www.mikestvtips.com/ 1-410-272-4984
When I first started in the TV repair business and my troubleshooting skills were not that great often times Mike's case histories told me exactly which parts I needed to replace and it often saved me from having to purchase a great many schematics. I have been using his case histories since 1995 and I would not be with out them. If you call him please be considerate of his time zone and call between 11:00 AM TO 8:PM Eastern time only.
Getting Started In Electronics by Forest Mims available at some Radio Shacks or through this link.



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