LG LW650T has no picture no sound. Have done many tests...Help

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LG Television

Repair guides and support for your LG TV.

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Dave @thedragon

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Postato: 7 feb 2021

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LG LW650T has no picture no sound. Have done many tests...Help

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

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jayeff @jayeff

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Postato: 8 feb 2021

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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.

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Hi @jayeff , thanks fo chiming in. Thanks for the link, I had a look around and seems the same copy I got from another site. You're right, it does say to replace board. I guess that's just how society has now become and "educated" to doso, either replace or buy new. It's quite unfortunate, as many electronic devices can continue to function much longer. I asked as two more repair specialists and they said they don't want to. Maybe I should do a electronics repair course ha,

8 feb 2021 da Dave

@thedragon

54 years ago I was taught electronics to be able to do board level fault finding and repair as an apprentice technician but when I left (after 40 years -deemed too old to be retrained in the newer technologies so I got out) it got to the point of becoming a board jockey (or should I say a “bored" jockey) as the equipment I worked on (telecommunications network switching) got to the point of having a maintenance computer telling you which board was the most likely problem and it had already switched it out of service and had the inplace standby board working in its place. The humans were only required to actually change the board which required not much skill except knowing how to locate it in the equipment rack and then to ship it back to the manufacturer who had an analysis PC that could detect where the most likely problem was on the board

It’s too expensive to train good techs and people don’t want to pay for their skills as they think that it is easy to do after all it's only a fuse ;-). Little do they know.

Cheers

8 feb 2021 da jayeff

Oh my, that's quite some experience in that field. I understand completely what you mean. I've worked in the IT field for about a decade, starting off in basic support then technician/building computers and then to field server supoort.

Whilst working as the technician, if a PC mainboard would malfuntion, we'd simply be told to swap it out. If a laptop mainboard deemed to be malfunctioning, the while laptop would be replaced and the broken one sent back to IBM/lenovo. The PC mainboards were either kept, scrapped or sent off somewhere. I was told by colleague who had been working there much longer, that in previous years, IBM would send their technician, who would then analyse the boards on site, and many times repair them at component level.

Now it's just not cost effective. I'm just an amateur, but have always tickered and tried sometimes succesfully repaired. As components have got so minuscule, its becoming impossible. I even repaired some of those PC boards, mostly capacitors. I just detest waste.

8 feb 2021 da Dave

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Hi @jayeff , thanks fo chiming in. Thanks for the link, I had a look around and seems the same copy I got from another site. You're right, it does say to replace board. I guess that's just how society has now become and "educated" to doso, either replace or buy new. It's quite unfortunate, as many electronic devices can continue to function much longer. I asked as two more repair specialists and they said they don't want to. Maybe I should do a electronics repair course ha, — Dave
@thedragon

54 years ago I was taught electronics to be able to do board level fault finding and repair as an apprentice technician but when I left (after 40 years -deemed too old to be retrained in the newer technologies so I got out) it got to the point of becoming a board jockey (or should I say a “bored" jockey) as the equipment I worked on (telecommunications network switching) got to the point of having a maintenance computer telling you which board was the most likely problem and it had already switched it out of service and had the inplace standby board working in its place. The humans were only required to actually change the board which required not much skill except knowing how to locate it in the equipment rack and then to ship it back to the manufacturer who had an analysis PC that could detect where the most likely problem was on the board

It’s too expensive to train good techs and people don’t want to pay for their skills as they think that it is easy to do after all it's only a fuse ;-). Little do they know.

Cheers — jayeff
Oh my, that's quite some experience in that field. I understand completely what you mean. I've worked in the IT field for about a decade, starting off in basic support then technician/building computers and then to field server supoort.

Whilst working as the technician, if a PC mainboard would malfuntion, we'd simply be told to swap it out. If a laptop mainboard deemed to be malfunctioning, the while laptop would be replaced and the broken one sent back to IBM/lenovo. The PC mainboards were either kept, scrapped or sent off somewhere. I was told by colleague who had been working there much longer, that in previous years, IBM would send their technician, who would then analyse the boards on site, and many times repair them at component level.

Now it's just not cost effective. I'm just an amateur, but have always tickered and tried sometimes succesfully repaired. As components have got so minuscule, its becoming impossible. I even repaired some of those PC boards, mostly capacitors. I just detest waste. — Dave

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LG LW650T has no picture no sound. Have done many tests...Help

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