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No backlight, but displays picture

Hi everyone!

I’m needing help trying to fix my TV. I have a D55un-e1, and the power supply board has the LED driver parts included (PLTVHU401XABV) Hyperlink to see picture of the board.

Did the flashlight test - there is picture, but NO backlight. Haven’t checked sound, but I’m assuming that it works since image shows (probable sign of T-Con and Main boards working).

I used the multimeter to test connection points on the main driver that goes directly into the panel. There are only 2 types of actual points - VLED and VLED 1. Everytime I read the points, I only get readings from VLEDs, but 0’s from VLED 1s. With the power on, I get the reading of 33.5 from all VLED points (only about 4 of them) and 0’s from VLED1 points.

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What could be the issue? I know it’s probably the LED inverters/driver board section of the power supply board, but I don’t see any burn marks nor lose capacitors/parts. I’m pretty new to this TV-fixing-realm, so I have no idea what could be the issue. I’ve even replaced the main board as well.

Would really appreciate the help!

Update (01/20/2021)

Thanks again for your help! I got my led tester, but with this power supply/led driver board, I’m not too sure where to stick the positive and negative needles (?)

Would you happen to know which goes where?

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Really appreciate it!

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Hi @johnny_k

One of the quicker ways to isolate the problem is to use a backlight tester (examples only) as this can be used to test the backlights without power being applied to the TV, thereby removing any “interference” by the boards as to whether they operate or not.

The tester is connected directly to the LED power supply lead which has been disconnected from the power board.

If the don’t work then it is in the LED backlights somewhere, either the connection to the backlights or in the LED strips themselves.

If they do work then it is harder as it may be in the power board since you have replaced the mainboard, but it still could be in the cable connection between the mainboard and the power board e.g. signal to turn on the LED backlights may be missing. Without a schematic of either board (I couldn’t find them anyway, you may have better luck) it would be difficult to know which wire this was on.

Usually there is audio when there is only a backlight problem so hopefully there isn’t something else as well.

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Thanks so much! Really appreciate the help! Will give it a try.. hopefully it’s not as difficult to fix.

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@johnny_k

Look on the board where the LED power cable plugs into.

the VLED leads are the +ve leads and the -VLED are the -ve leads

The pin count is shown on the board i.e. 1 down the bottom or on the right when looking at the image you posted and 12 at the top or the left.

So place tester between pins 12 (+ve) and pin 10 (-ve) ON THE PLUG, (which is disconnected from the socket)

Then between pin 11(+ve) and 9 (-ve), then presumably between pin 2 (+ve) and pin 8 (-ve) and then pin 1 (+ve) and pin 7 (-ve)

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Johnny K zal eeuwig dankbaar zijn.
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