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LG 55UH950V Backlight issue

A family member has asked me to have a look at their LG TV. It’s a 55UH950V and they have said it has started ‘turning off.

It’s not though, the backlight is going off. If I shine a torch you can see the dim display.

There is no trend to how long it lasts, sometimes it’s over a minute, sometimes it is a few seconds before the screen dims.

As soon as the backlight goes off the orange indicator light on the power board flashes 4x in sequence.

I am thinking it could be the power board as the backlight looks fine until it goes dim.

Any ideas?

Update (07/14/24)

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Block Image

Which 18V do I test on the board?

I have done a couple out backlight changes on a 55” in the past but not an edge lit so that will be new to me, if they need changing!

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@chris90813 jumper J53 and J29 both must have 18V

da

Well I have a resolution but another question to go with it.

I am getting 18v on Pins 1.2.3.4 and on J29 and J23.

I get 18v over on the mainboard too.

I turned the TV on and quickly set the backlight to 20 and it stayed on for 15 mins. LED flickered on the bottom backlight array and the TV turned off, so it seems there is a backlight / LED issue?

Before I go ahead and order new strips I have another question.

There is a really strong yellow tint at the top of the TV down to midway and then it is a normal colour.

Is that simply the upper backlight or is it the panel?

da

@chris90813 yes, all

Of this sounds like a bad LED backlight strip. Replacing those strips should fix all of these issues.

da

I have ordered a set of strips. Will report back when they arrive and I have installed them.

da

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Hi @chris90813

Here's the service manual for the TV.

Go to p.40/78 (no video/normal audio troubleshooting) and p.72/78 (Power error/no power) to see how to check the voltages.

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That’s great, thank you!

da

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@chris90813 could be a power board issue. Check for the 18V on the board. If you show the proper voltage than you know you are either looking a bad inverter or bad backlight strips. Your LG may give you a 4 blink error code because of the feedback from the backlight detecting that there are failed LED's. Sometimes you can bypass this error detection. For that we really would need to see all of your boards etc. Some images must show the connectors to the power board and the main board. Aggiungere immagini ad una domanda

Ultimately, knowing the it is an LG and knowing that those have issues with bad back lights, I would definitely focus on that.

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I was thinking power board because the backlight seems absolutely fine, it can run for a minute or two and then the backlight just goes completely.

The TV keeps running, sound is on, just no backlight. The image is there if you shine a light at the panel.

Not seeing any sign of any of failed or failing LED’s before it goes off. The picture quality looks good.

The boards visually look fine, no bad capacitors.

I’ll check the 18v on the board.

da

@chris90813 agree. It's my first suspect when it comes to symptoms like your TV and being an LG.Time to disassemble the panel and to replace the backlight. Not a terribly complicated job just a PITA dues to the size of the panel. Make sure you do not flex the screen and have an extra set of hands available.

da

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Chris sarà eternamente grato.
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