Samsung UE55D8000 not powering up

[rajembt]

Hi guys

I have a Samsung UE55D8000 which has no standby light and no backlights. There is not even a click from the relay on the power supply board (BN44-00428A).

I removed the power supply board to check some components such as the rectifier, resistors,etc. Some electrolytic capacitors were showing slightly high ESR so I replaced them all as I had the board out anyway.

On putting the power supply board back in I got exactly the same symptoms.

If I disconnect the cable from the power supply board to the main board, then there is a click from the relay, but no backlight display.

If I remove the cables from the power supply board going to the LEDs (CNL802A and CNL802B) and leave the main board connected to the power supply board then again, there is nothing - no relay click.

I measured some of the voltages at the pins (CNM803) with the main board disconnected from the power supply board:

Pin Descriptor Measurement(V)
1 OD_level 5.32

3 OD_on/off 5.12

5 GND 0

7 B13V 12.77

9 B13V 12.77

11 Vamp 17.08

13 Vamp 17.08

15 GND 0

17 B5V 5.42

19 B5V 5.42

21 N.C

2 P_DIM4 0

4 P_DIM3 0

6 P_DIM2 0

8 P_DIM1 0

10 B13V 12.77

12 BLU 4.76

14 GND 0

16 GND 0

18 A5V 5.41

20 POWER ON/OFF 3.39

22 N.C


These voltages seem to be OK according to the stamp on the board (see attached)
So I could do with some assistance on where to go from here please.

According to the previous owner, the TV was fully working but gradually got worse until eventually it stopped powering on altogether.

Any help would be much appreciated.
Thanks

[budm]

Re: Samsung UE55D8000 not powering up

Can we the pictures of the whole backside of the TV showing all the boards and the picture of the whole power supply board?
What Voltages do you have on the LED connectors when main board is not connected to the power supply board?

[rajembt]

Re: Samsung UE55D8000 not powering up

Thanks for the reply.
Sure, here are some pics of the whole backside and the whole power supply board.
Also a pic of the voltage readings when the main board is disconnected from the power supply board.

[rajembt]

Re: Samsung UE55D8000 not powering up

An update:

After taking readings, I thought that the Main Board may have been at fault.
I replaced it with a known working one, and I still have exactly the same symptoms as before.

Can anyone advise where to go from here?

[neilc6]

Re: Samsung UE55D8000 not powering up

You need to confirm your backlights are good before suspecting any of the boards.

[rajembt]

Re: Samsung UE55D8000 not powering up

What would be the easiest way to do this?
I have disconnected the main board from the power supply board, and the backlights do not light up, but is there some other process I need to do for that to happen on this model?
Thanks

[neilc6]

Re: Samsung UE55D8000 not powering up

I have disconnected the main board from the power supply board, and the backlights do not light up
Thanks

Failing this test indicates you have a problem with the backlights and/or power supply. The main board doesn't even come into play. Difficult to test the led strips without a LED tester, especially edge lit strips.

Edit: You can monitor the voltages going to the strips when the tv turns on which may give an indication if the strip has shorted or open leds.

[budm]

Re: Samsung UE55D8000 not powering up

https://www.badcaps.net/forum/attach...2&d=1557405670
Too bad you did not put down the pin name and number for each one of those pins so we easily see the issue.