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Manufactured December 2013. Model Number: 47LN575V - ZE

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What do I replace to fix failed backlights?

Hi guys, the tv powers on and plays sound but the picture has gone dark. The picture is visible if you really try to see it so i have assumed it is the backlight inverter that has failed. The only problem is… i have no idea where it is on this tv. I saw on another post someone say it was on the power board, but is there any way i can fix this without having to replace the whole board? I want to get into repairing so changing components is fine with me.

Any help is really apreciated.

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Hi @jackem

Looking at an image of the layout on p.74 of the service manual it appears that the LEDs are powered from the power board and not a separate inverter board unless the board is mounted under the metal plate, on the back of the screen itself, of course.

The trouble shooting flow chart shown on p.92 (see image below) suggests that if the 24V on the power board is OK then replace the inverter or the module. Usually the word “module” is terminology used to mean the LCD panel.

Block Image

(click on image to enlarge for better viewing)

Looking at images for the power board online it appears that there is a separate connector that is used to connect a cable to, to supply power to the panel LEDs. The connections are marked as LED+ and LED-. Hopefully I’ve found the right one and yours is the same.

I haven’t scoured the whole manual to find the schematics for the power board but a quick look suggests that it may not be there. It is hard to use the manual as you have to select each page one at a time to view it. To download it requires signing up with the website, which I didn’t want to do.

If you prove that the LED power supply is the problem and there are no schematics for it in the manual then perhaps searching for the (insert power board board number) schematics may get results. The board number is printed on the board itself or maybe it is on a barcode sticker.

Finding board level faults without a schematic is very hard unless the problem is an obviously damaged component or perhaps a sign of heat stress etc.

Also have you checked that it isn’t the LEDs themselves that are the problem?

Using a TV backlight tester (examples only) is a quick way to know whether the problem is with the LEDs or the power supply to the LEDs as it tests them independent of power having to be connected to the TV. You just connect it to the LED power supply cable which has been disconnected from the power board. Might save a lot of time wasted unnecessarily looking for a problem in the wrong place because it is not there to be found.

Be safety aware when testing for the voltages on the power board. Even though you are testing for low DC voltages there is exposed lethal AC voltage on the power board near to where you may be testing. If you don’t know how to test safely when high AC voltage is present then don’t do it!

Hopefully this is of some help

Update (04/05/2021)

Hi @jackem ,

Before you try to find a LCD panel (which may not be that easy to find or if you do then the price is not worth it) did you check the voltage to the LEDs from the power board?

I’m not quite sure where you meant that the 24V was fine, the power board connector to the mainboard or the LED power connector. I’m not sure if there is 24V to the LEDs though so set your Voltmeter to the highest measurement scale as a safeguard and then lower the scale to suit for more accuracy.

Here’s an image of the power board (hopefully yours is the same) where I’ve highlighted where I think that the LED connector is. It is a bit hard to see but maybe there are pins on the connector that are marked LED+ and LED-. If you measure between the LED+ and an Earth point (a screwhead on the board should be earthed to the chassis) you should get a reading.

Block Image

(click on image to enlarge for better viewing)

Also it may be worth investing in a backlight tester and testing the LEDs first, as it will be a lot cheaper than a panel and if it is the power board and not the panel, then both i.e. power board and tester would still be cheaper than a panel.

Maybe by using the tester you’ll find that it is the LED strips themselves that are the problem. (supplier example only)

There are videos on YouTube that describe how to replace the LED strips in a TV but make sure that you find one for your model (or very close) as a panel comprises diffuser sheets as well so you have to know how to dis-assemble it so that you re-assemble it correctly. Either that or take pictures as you dis-assemble ;-)

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2 Commenti:

Thanks a lot, this was more than I expected. I really apreciate it.

da

I have tested the power and the 24v is fine, to fix this would i need a new lcd screen?

da

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Jack sarà eternamente grato.
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