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Samsung UN32EH5000F won't power on when dim control connected to PSU

I have a Samsung UN32EH5000F. Replaced the power board and the main board but still cannot power on. What I have found when I unplug the backlight dim control I can power it on but not when is plugged back. The plug for the backlight dim control (CNL802) says D-, S+, S-, and D+. I have BLU power 4.86V to the backlight after some delay on the main board.

Any clue what could be wrong? Thanks

Update: 2/29

It looks like CNL802 has those voltages:

  • when the TV is turned off: D+: 155V, D-: 0V
  • when the TV is turned on: D+: 152V, D-: 1.4V

Should I measure it D+ to D- and S+ to S- instead of all of them to GND?

Update: 3/1 AM

Single board on a pic - old board

Two boards on a pic - two replacement boards

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Update: 3/1 PM

It looks like some of the backlight LEDs are dead

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Update: 3/9

Replaced LED strips - problem solved!

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Beantwoord! Bekijk het antwoord Dit probleem heb ik ook

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@jackthekni80531 disconnect the power cord from the power board. Then disconnect the main board from the power board. Next plug your power cable into the power board. Your back lights should come on. What did you get?

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@oldturkey03

How it can work when there is no BLU signal from the main board (is disconnected) to power on the backlight? I have tried and did not work because CNL802 is plugged in which causes some issues as I have mentioned above.

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@scyzoryk "How it can work when there is no BLU signal from the main board (is disconnected) to power on the backlight?" It is your main board that tells your power board to power up the back lights circuit. When you disconnect the mainboard the power board closes that circuit and supplies power to the backlight LED's Of course you only have the backlight and no image etc.

Since you have already tried it and it did not work, yet you have the right voltages to the LED backlights, you want to replace your backlight strips. The 110V is correct. Your LED driver should have something like a 90V output which will be higher under a "No load" All of this points to your LED backlight strips.

BTW "BLU power 4.86V to the backlight after some delay on the main board" is cordt to since your mainboard has a 5 sec delay on that circuit.

Luckily its a relatively small panel and fairly simple to take apart. Just mark each diffuser and polarizer sheet exactly in the order and direction in which they are layered. Not a bad tasks for a decent TV.

Update (03/01/24)

@scyzoryk do you still have your old power board? What was the number on that? What is the part number for the new one? Post some pictures of the top and bottom side of the old and new power boards with your Question. Voeg afbeeldingen toe aan een bestaande vraag

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Just got an LED tester so I was able to test the backlight. When I have powered on S+ and D- it lit. When I do S- and D+ it will light too.

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@oldturkey03

Pics added to the OP. Single board on a pic - old board. Two boards on a pic - two replacement boards

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@scyzoryk GReat. Thanks for the pictures. Just erified that that board is the right one. There have been situations with this TV that wrong boards have been sold as compatible that actually weren't. All the voltage are right everything checks out on your board. Open the panel up and check your LED strips. I know that the tester turned them on but you still want to check them since all he voltages on your board are what they are supposed to be. That puts it once more back at the panel and the backlights. Split the panel and then connect your tester. Let us know if and how many lights are out. There should be two strips with 12 LEDs each connected in series.

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@oldturkey03 OK, looks like some of the LEDs are dead (added photos as reference). Based on that looks like the PSU or the main board is checking the voltage feedback from the backlight and will not turn on the TV to prevent further damage,

Do you have any reliable source from where to get replacements?

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@scyzoryk quickest and relatively inexpensive buy would be from ebay, Amazon or Aliexpress. Not the greatest of all quality but inexpensive. I prefer this seller but of course you can purchase from wherever you prefer. No personal benefits from stating my preference :-)

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