Samsung UE55KU6470U no display, display switching on and off when powered on

[Themi]

Hi all

My UE55KU6470U has developed a fault. When powered up, the display switches on and off. This just repeats. Is there anything I can do to repair it?

I intend to take the back off and give the boards a visual inspection. Never repaired a tv before but I gather there are power, logic, backlight and lcd connector boards?

My initial guess would this might be a power board issue?

I'm happy to walk through some diagnosis steps and check individual components. I've got a decent hand re soldering down the bga level and some microelectronics experience but not an expert by any means.

Thanks all

edit: here a vid showing the current state of the tv https://streamable.com/6uyhga

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

ok so removing the back of this tv looks like it will be a challenge in itself.

I've found this video and whilst not my exact model I'm guessing the process for removing the back will be similar (sigh)

time to find the spudgers...

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Well the back is off. Not sure if it hurt me or the tv more. Only broke a single lug on the surround which I’ll epoxy back once finished.

Here are some initial pictures of the board. It’s pretty late here but I’ve given them both a quick once over and see nothing out of the ordinary. Will try again tomorrow with fresh eyes.

[Kilroy2k1]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

For a quick backlight test, unplug the unit from mains, then unplug the cable between the main board and the power supply and when you plug the unit back into the mains, it should light the backlights up.

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

For a quick backlight test, unplug the unit from mains, then unplug the cable between the main board and the power supply and when you plug the unit back into the mains, it should light the backlights up.

Thanks for that. I am guessing this means the backlights and it's circuit + board are working?

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Some more images.
Checking voltage from the power board. Not entirely sure if these are ok




Going to remove it and give it a check over on both sides

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Power board is out.

Underside doesn’t appear to have anything wrong after a visual inspection. As a note, it appears to be covered in a thick silicone or glue. Is this normal for Samsung tv power boards. Looks awfully messy.

Some images anyway

[Davi.p]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Detach the screen to mainboard cables and try again with all the rest connected.

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Detach the screen to mainboard cables and try again with all the rest connected.

ok so removed the two flat ribbon cables to the screen and the same behaviour.

screen + backlights come on and both go off and it repeats

looking like the power board?

[Kilroy2k1]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

I just worked on a samsung with the same kind of issue. What i found was a shorted component on the little buffer boards that those ribbon cables connect to at the screen.
If you remove the speaker and that metal strip under it you'll see the boards I refer to.
Some models that board is 2 pieces connected with another ribbon cable. you can disconnect the little ribbon cable one at a time and see if the tv power cycles.

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

I just worked on a samsung with the same kind of issue. What i found was a shorted component on the little buffer boards that those ribbon cables connect to at the screen.
If you remove the speaker and that metal strip under it you'll see the boards I refer to.
Some models that board is 2 pieces connected with another ribbon cable. you can disconnect the little ribbon cable one at a time and see if the tv power cycles.

ok I'll take a look now. What was the component out of curiosity?
I've just tried an alternative power board (was worth a punt for £5) and no dice, same behaviour.

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Longer than I thought.




I’ll inspect them

Any tips for testing?

Looks mainly to be caps, a few diodes and a mosfet

Edit: oops not a mosfet but flash memory

[Davi.p]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

I think it's a bit uncommon that with or without the screen connected is the same behaviour, it is possible a software fault.. how many seconds passes between switch on and off and from off and on? Remove the heatsink on mainboard and take a photo of it hires and at sunlight. But change the way you attach it because otherwise the page become too heavy..

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

I think it's a bit uncommon that with or without the screen connected is the same behaviour, it is possible a software fault.. how many seconds passes between switch on and off and from off and on? Remove the heatsink on mainboard and take a photo of it hires and at sunlight. But change the way you attach it because otherwise the page become too heavy..

image of the board with heatsink removed
https://ibb.co/2k4xtTR

2x 6-7 second gap then one longer 11 second gap, this repeats twice

after this only 6-7 gap continuously

edit: I do have an IC read/write usb if needed

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Longer than I thought.




I'll inspect them

Any tips for testing?

Looks mainly to be caps, a few diodes and a mosfet

Edit: oops not a mosfet but flash memory

I've had a look along the two boards, can't see anything interesting.
Not entirely sure how to test some of the components

https://ibb.co/M6FYsB5
https://ibb.co/hCmXYG5
https://ibb.co/kxk6TzL
https://ibb.co/gR2vxtF
https://ibb.co/gb2jD7C

[Kilroy2k1]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Darn your boards are singles.
The bad part on mine was a tiny little 10 pin diode array right near the end of the board.
For testing start with the caps. Unplug the LVDS cable, put your meter on continuity and test all the caps for shorts. Then switch to ohms and test the values of all marked resistors.

[Davi.p]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

To post correctly use POST REPLY button and then use "paperclip" icon...
if you are able, locate the points on mainboard named like AVDD, HAVDD, V1.8, V3.3, VGH, VGL, and with all connected test those points in volt. *= VGL can be VOFFE, VGH=VONE

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Ok guys so I had another look

I received a cheap mainboard today and swapped it out but still receiving the same problem.

My partner spotted a flash coming from the corner of the panel where it is connected to one of the tcon boards.

I inspected and it looks like a part of the ribbon leading to the tcon from the panel has burned and this is causing the spark / short. The sparking happens intermittently as the screen is powered on.

There are images and a video below.

I am guessing this is the end of the road for this panel?

https://ibb.co/nDPbGtz
https://ibb.co/b7wc9z5
https://ibb.co/7RMqWfV

Here is a video in slow motion as the spark is so quick it was the only way we could capture it.

https://streamable.com/5wzv67

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

So strange things are happening

I decided to give up knowing there was a short from the panel or irreplaceable tcon board + connection as I can’t reliably repair the screen.

I removed the new parts I added and reinstalled the original parts and decided to take photos to sell as spares and repairs then this happened...



Wtf

[Themi]

Re: Samsung UE55KU6470U no display, display switching on and off when powered on

Well it’s certainly up and running.

However there are lines across the screen. I guess that’s from the missing conductor in the ribbon. Still not too bad though