Samsung TV UN55KU6490 not working

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masiyagu+cnd @masiyagucnd

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发帖于: 2022年9月10日

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Samsung TV UN55KU6490 not working

Hi People!

Please, note that my TV is UN55KU6490 and not the UN55MU6290 ***

I have a defective Samsung TV UN55KU6490. The PS board is BN44-00807A and the main board is BN94-10827Q. There are only these two boards.

The screen is always black.

Whenever it is powered-on, I can hear a weak sound on the speakers, like the Samsung "Welcome" sound; it happens only once. The back panel LEDs cycles Full On -> Dim -> Off, in cycles of about 10s.

I download the service manual from a similar model, and I was able to go through some tests:

On the PS board:
1. Disconnecting the cable between the PS and Main board, all the back panel LED lights up, stay on, and I could measure 266Vdc and 132Vdc on CNL802 connector
2. There is the 12.8Vdc.
  1. While the TV is on Standby, it is steady at 12.8V;
  2. When the TV is Powered On, it stays at 12.8V and quickly drops to 8V about every 10s.
On the Main Board:
1. I could measure the voltages on the joystick button, and they change accordingly (0; 0.5V; 1V; 1.5V; and 1.8V)
2. The is 5V on the USB ports
3. I'm not 100% positive about it, but it seems the PS_ON keeps at 3.3V and quickly drops to around 2V, following the 10s cycle. It is pretty awkward to measure this signal (at least to me...).

Following the service manual, it looks like the defect is on the Main Board.

Is it correct?

Any other test that I should do?

Any tips?

Finally, what is a good site to buy the board (refurbished / used)?

****

I've added some pictures from the boards.

****

Thank you!

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Can you take pictures of the main board and power supply board and upload them here? 在已经存在的问题里加入图片

由 Andrew S 完成的 2022年9月10日

Hi @andrewsawesome,

I've uploaded some pictures.

Thank you!

由 masiyagu+cnd 完成的 2022年9月11日

Hi Folks,

I had no luck replacing the TV boards.

Initially, I've diagnosed the main board as the culprit. I ordered it and replaced it, but the results were the same.
Then I've ordered and replaced the power board. Again, no success.

I've made 2 videos: with the original and new boards to show the situation. I've tried to upload them many times in different formats, resolutions, etc..., but I keep getting an error message, and I don't have a clue how to fix.

Here are the links to my Dropbox with the 2 videos:

https://www.dropbox.com/s/fvie6zwlq5jeyu...

https://www.dropbox.com/s/ha7cmfn8iqboia...

Hopefully, the people will be able to access them.

Please, let me know if you have any other clue or suggestion about the issue with the TV before I consider it lost for good.

Cheers!

由 masiyagu+cnd 完成的 2022年10月29日

@masiyagu+cnd looking at your videos, when you disconnect the main board from the power board, your backlight should stay on. Video #2 shows them on/of. Is that the way it is when you disconnect the board? If so, it is your backlight array. BTW your panel does look odd as well. Video #1, check the right side of your panel when your TV comes on. You get lines and some "bleeds" That is not the way this should look. Have you checked the boards that connect directly to the panel? Check for burned componentes etc. on those. Carefully, the ribbon cables form those boards to the panel are very flimsy an love to come unglued.

由 oldturkey03 完成的 2022年10月29日

Hi @oldturkey03!

Thanks a lot for the comments.

When I disconnect the cable from main to power board, the backlight stays on with either power board.

I've also visually searched for damaged components on both boards. Didn't find anything suspicious.

The cables from the main board to the panels seems good, but I didn't check them for continuity. I sprayed some electronic contact cleaner on them between the trials, again with no success.

Other thing that I've tried was to disconnect the speaker, wifi board, and Remote Control board, and power-on through the joystick, just in case those boards had any defect. No changes on the behavior.

I think I tested and tried as much as I could. I only have a simple multimeter.

It looks like it is time for a beer...

Cheers!

由 masiyagu+cnd 完成的 2022年10月29日

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Can you take pictures of the main board and power supply board and upload them here? 在已经存在的问题里加入图片 — Andrew S
Hi @andrewsawesome,

I've uploaded some pictures.

Thank you! — masiyagu+cnd
Hi Folks,

I had no luck replacing the TV boards.

Initially, I've diagnosed the main board as the culprit. I ordered it and replaced it, but the results were the same.
Then I've ordered and replaced the power board. Again, no success.

I've made 2 videos: with the original and new boards to show the situation. I've tried to upload them many times in different formats, resolutions, etc..., but I keep getting an error message, and I don't have a clue how to fix.

Here are the links to my Dropbox with the 2 videos:

https://www.dropbox.com/s/fvie6zwlq5jeyu...

https://www.dropbox.com/s/ha7cmfn8iqboia...

Hopefully, the people will be able to access them.

Please, let me know if you have any other clue or suggestion about the issue with the TV before I consider it lost for good.

Cheers! — masiyagu+cnd
@masiyagu+cnd looking at your videos, when you disconnect the main board from the power board, your backlight should stay on. Video #2 shows them on/of. Is that the way it is when you disconnect the board? If so, it is your backlight array. BTW your panel does look odd as well. Video #1, check the right side of your panel when your TV comes on. You get lines and some "bleeds" That is not the way this should look. Have you checked the boards that connect directly to the panel? Check for burned componentes etc. on those. Carefully, the ribbon cables form those boards to the panel are very flimsy an love to come unglued. — oldturkey03
Hi @oldturkey03!

Thanks a lot for the comments.

When I disconnect the cable from main to power board, the backlight stays on with either power board.

I've also visually searched for damaged components on both boards. Didn't find anything suspicious.

The cables from the main board to the panels seems good, but I didn't check them for continuity. I sprayed some electronic contact cleaner on them between the trials, again with no success.

Other thing that I've tried was to disconnect the speaker, wifi board, and Remote Control board, and power-on through the joystick, just in case those boards had any defect. No changes on the behavior.

I think I tested and tried as much as I could. I only have a simple multimeter.

It looks like it is time for a beer...

Cheers! — masiyagu+cnd

oldturkey03 @oldturkey03 声誉积分: 782.2千 1.1千 893 2.3千 · Answer 1 · 2022-09-11T07:07:16-07:00

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oldturkey03 @oldturkey03

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masiyagu+cnd your power board is okay. Glad you tested that. This does sound like a main board issue the only thing that is weird is this "Welcome" message. Does it sound like it did before? I would focus on the main board. Post some good images of your boards and the interconnect cables with your QUESTION 在已经存在的问题里加入图片 That way we can see what you see.

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Hi oldturkey03!

Thank you for the reply.

By the "Welcome" sound, I meant that short music the Samsung TV play when they are turned on. The point is that is very low volume. There is no image at all.

I'll move ahead and buy a new main board. Any tip for good sites to buy it?

Once I replace it, I'll let you know the result.

I've attached some pictures to the original post. No visual signs of damaged components in any of the boards.

BR,

由 masiyagu+cnd 完成的 2022年9月11日

@masiyagu+cnd shopjimmy.com is the best but there might be cheaper alternative. see what you can scour on ebay etc. since used is okay as well.

由 oldturkey03 完成的 2022年9月11日

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Samsung TV UN55KU6490 not working

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