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Old 05-27-2020, 04:09 AM   #1
axon18
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Default Lg 32lb5700 no power on led

Good Morning,
I have a TV that suddenly stopped showing pictures. After searching in the internet, i find that could be the LED tapes. I opened the TV and it really had a burnt and scorched tape led ... i replaces them all.
When I connected everything is the same.
Can you help me?

I attach the photos and measurements on and off.

Sorry my bad english.
Attached Images
File Type: jpg 20200526_200718.jpg (696.5 KB, 7 views)
File Type: jpg 20200526_200738.jpg (729.2 KB, 12 views)
File Type: jpg 20200526_200833.jpg (617.7 KB, 6 views)
File Type: jpg 20200526_200857.jpg (666.8 KB, 6 views)
File Type: png OFF.PNG (266.7 KB, 7 views)
File Type: png ON.PNG (189.4 KB, 8 views)
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Old 05-27-2020, 04:43 AM   #2
dick_barton
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Default Re: Lg 32lb5700 no power on led

You are missing a signal from the mainboard to turn the leds on. DRV_On should be approximately 3.5V
Disconnect the mainboard from the power supply and connect a 1K resistor from 3.5V to PWR_On and a second 1K resistor from 3.5V to DRV_ON
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Last edited by dick_barton; 05-27-2020 at 04:48 AM..
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Old 05-27-2020, 08:15 AM   #3
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Default Re: Lg 32lb5700 no power on led

Hello
your board need to be reball CPU !!!!
do not tuch any thing !!!
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Old 05-27-2020, 09:14 AM   #4
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Default Re: Lg 32lb5700 no power on led

Quote:
Originally Posted by salarsat View Post
Hello
your board need to be reball CPU !!!!
do not tuch any thing !!!
That's just a HUGE assumption.
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Old 05-28-2020, 03:52 PM   #5
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Default Re: Lg 32lb5700 no power on led

Quote:
Originally Posted by dick_barton View Post
You are missing a signal from the mainboard to turn the leds on. DRV_On should be approximately 3.5V
Disconnect the mainboard from the power supply and connect a 1K resistor from 3.5V to PWR_On and a second 1K resistor from 3.5V to DRV_ON
Hello, i make what you said and the led poweer on, then i disconnectt the led and check 142vdc in led connector.
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Old 05-29-2020, 01:56 AM   #6
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Default Re: Lg 32lb5700 no power on led

So the backlight works when you tested using the resistors, yes?
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Old 05-29-2020, 02:00 AM   #7
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Default Re: Lg 32lb5700 no power on led

Yes
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Old 05-29-2020, 02:29 AM   #8
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Default Re: Lg 32lb5700 no power on led

It looks like you have a mainboard problem not providing the signal and your leds are OK.

Can you follow the DRV_ON pin on the mainboard and see if it connects to a transistor/mosfet.
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Old 05-29-2020, 02:47 AM   #9
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Default Re: Lg 32lb5700 no power on led

Or reflow to the processor.
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Old 05-29-2020, 04:53 AM   #10
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Default Re: Lg 32lb5700 no power on led

Quote:
Originally Posted by dick_barton View Post
It looks like you have a mainboard problem not providing the signal and your leds are OK.

Can you follow the DRV_ON pin on the mainboard and see if it connects to a transistor/mosfet.
After search i find that c701 is missing, there is olny the place with solder.
I attatch picure with the pin DRV_ON and the component that is missing.
And i don't know what is...i search the board but i can't find the manual..eax65610905
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Old 05-29-2020, 05:17 AM   #11
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Default Re: Lg 32lb5700 no power on led

Why would the smd capacitor C701 be missing? It does look as though it is. Was this TV working for you or do you have it for repair? Has the mainboard been replaced or worked on?
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Old 05-29-2020, 05:36 AM   #12
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Default Re: Lg 32lb5700 no power on led

The television was working. It was on a living room sideboard and then I posted it on the wall. after that it worked a few hours.
It wasn't to fix. It won't pay off. Appliances are very expensive to repair here.
Can you tell me what componet i have tu buy tu put there.. to see if works.
Regards
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Old 05-29-2020, 05:42 AM   #13
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Default Re: Lg 32lb5700 no power on led

Unfortunately, I do not know what the component is.
Perhaps someone with an identical board could tell you but there would be no guarantee that that is the only problem. There also appears to be an smd resistor alongside that is not in circuit so it may be that they were never included in this version of the mainboard.

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Old 05-29-2020, 05:55 AM   #14
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Default Re: Lg 32lb5700 no power on led

That's where a MLLC capacitor would go, see all the others, look around tho, maybe this setup did not require that cap, there are many more places on that board that don't have those caps in place, see them, just because there's a place for one does not mean it was needed in this particular setup/configuration.

Last edited by nomoresonys; 05-29-2020 at 05:56 AM..
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Old 05-29-2020, 07:35 AM   #15
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Default Re: Lg 32lb5700 no power on led

Quote:
Originally Posted by axon18 View Post
After search i find that c701 is missing, there is olny the place with solder.
I attatch picure with the pin DRV_ON and the component that is missing.
And i don't know what is...i search the board but i can't find the manual..eax65610905
That's definitely looks broken off, non filled pads have more rounded solder domes. I have an identical board here and have just pulled that capacitor, it's 10uf.
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Old 05-29-2020, 07:45 AM   #16
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Default Re: Lg 32lb5700 no power on led

Quote:
Originally Posted by diif View Post
That's definitely looks broken off, non filled pads have more rounded solder domes. I have an identical board here and have just pulled that capacitor, it's 10uf.
There's also an smd resistor in the photo I posted that I could not see on his original photo. Is it on your board and can you see its value.
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Old 05-29-2020, 08:42 AM   #17
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Default Re: Lg 32lb5700 no power on led

It's tiny and black which is why it doesn't look like it's there. It's in circuit with the two black devices either side of it, it sits lower than them so it's very unlikely it could be knocked off, unlike that cap.
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Old 05-29-2020, 12:29 PM   #18
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Default Re: Lg 32lb5700 no power on led

Yep, looks like it fell off or was removed, what's the tv history? another pic. there: https://www.ebay.com/itm/LG-32LB570V...-/273575219348

Last edited by nomoresonys; 05-29-2020 at 12:35 PM..
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Old 06-02-2020, 04:44 PM   #19
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Default Re: Lg 32lb5700 no power on led

Good evening,
Thank you all for your help. I ended up buying a new card.
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Old 06-02-2020, 06:38 PM   #20
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Default Re: Lg 32lb5700 no power on led

Ok, let us know if it works.
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