Chosen Solution
My LG LW650T suddenly stopped working a few days ago, and although I’ve started the search to replace it as it was old, the picture quality was good and would love to repair if possible to use elsewhere and save some electrical waste.
I gave it to a local repair place who said he would do some basic checks, and reflow it, but it never worked so didn’t charge me.
Turning on via RC I hear the relay turn on, the main power LED turns on the the other control LEDs cycle on/off as normal. The power LED goes off but the relay does not click off. (I had set this option years ago for power LED to turn off when wathcing TV).
There is no backlight. I pressed menu on the RC and then shone a light into panel and could not see any image. Press the RC power btton, turns off the TV, as I hear the relay click.
Searching on here and other places on the internet, I have done some testing with my limited knowledge of electronics, saving peoples time.
All PSU voltages are present that connect from PSU to Main board.
On standby all 3.5v rails are fine .
Turning on via the remote
12v rails read 11.8v
24v rails read 24.1v
3.5v rails read 3.5v as before.
I also jumped the PSU board connector- 3.5v to Power On, 3.5v to DRV On. Applying power I hear the relay and the backlight turns on. I get 56v at the 4 LED+ points. Further investigation I read about TCON, and find that it is not gettting 12V from the mainboard. The fuse on the TCON board is ok. Following some guides, I have tried to trace the 12V voltage from main board, which goes through Q505,Q506 transistors and Q507 mosfet. This is the bit thats beyond my knowledge, I dont know exactly where to follow the final 12V through to output. I did find the 12v coming into the Panel Power section. Out of curiosity, I found the same Q507 mosfet used by the CI card slot (UK model). So I unsoldered it and replaced the Q507 with it. TV still does not work. So now I am stuck, as to why the TCON is not getting 12v. Oh btw I had removed the heatsink myself to check Can anybody shed any light. Thank you
Hi @thedragon , I don’t know the answer and I don’t know if this will be a help or not but here’s a link to a section of the service manual that shows panel power in the diagrams. There are no schematics as such in the manual only limited diagrams as to individual functions/sections of the TV. Even the No video/no audio troubleshooting flowchart on p.56 says to replace the mainboard if the voltages check out OK on the power board. Obviously not interested in board level repairs The manual is a bit difficult to use online as you have to keep changing the page number in the box below the page and click on Go when wanting to change pages. To download it you have to sign up to the website.
