Samsung UN50J5200AFXZA - Screen goes blank

[Redwood]

I just picked up a free Samsung UN50J5200 that seems like it should be worth saving. It powers up but only briefly displays a gray bar across the top 2" of the screen, which gradually fades to black starting at one side and working across the screen over a period of less than a minute. After that, nothing.

The backlights work and stay lit indefinitely.

The power supply puts out in the range of 12V to the main board, but curiously the DC voltage to the LEDs is very high - like over 200VDC. Is that normal? I would expect more like 40VDC. Is it just a really long string of LEDs in series requiring such high voltage or is there something faulty in my PS?

Beyond that, I get ~3V out of the main board into the TCON board, and ~1.2 to 1.8V output from the TCON board to the panel bond boards. I can't find any overt signs of damage anywhere.

Nor can I find a schematic or service manual for this set. I've read everything I can find and wasted hours on YouTube trying to figure out how to determine if the panel is bad and gotten nowhere.

Seems like this was a really common set sold at Costco a couple years back so I'd think there are a lot of them on the street. Any pointers would be appreciated.

[budm]

Re: Samsung UN50J5200AFXZA - Screen goes blank

We need to see the pictures of the whole backside of the TV showing all the boards.
backlights are fine otherwise they will not stay on.
Try having ribbon cables between T-CON and the LCD panel connected one at time to see what happen.

[Andrew F. Ali]

Re: Samsung UN50J5200AFXZA - Screen goes blank

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[Redwood]

Re: Samsung UN50J5200AFXZA - Screen goes blank

We need to see the pictures of the whole backside of the TV showing all the boards.
backlights are fine otherwise they will not stay on.
Try having ribbon cables between T-CON and the LCD panel connected one at time to see what happen.

Thanks very much for the response. Please see attached photos:

1- Entire rear panel
2- Power supply board
3- Main logic board
4- T-CON board
5- Panel bond board (left side from rear of TV)
6- Display with left (from rear) panel bond board disconnected from T-CON board

When I removed the LEFT (from rear) panel bond board connection, the opposite side (LEFT from front) of the TV display appeared to work normally - this is the first time I've seen any image on the screen at all.

When I reconnected the LEFT (from rear) side and disconnected the RIGHT (from rear) panel bond board, I got nothing on the screen at all, not even the disappearing horizontal grey bar across the top that happens when both are plugged in.

I am hoping this points clearly toward a solution but I have no idea if it's the T-CON board (which would be great!) or the panel bond board (which would likely be bad since they don't look easily replaceable).

Thanks again!

[budm]

Re: Samsung UN50J5200AFXZA - Screen goes blank

You have bad LCD panel.
This LCD panel has tab bonding board on the bottom edge of the board and they usually get damaged by the cleaning liquid when people do the screen cleaning.
The problem can also be caused by the shorted caps on the tab bonding board, you will have to take the metal frame off the LCD panel to inspect and check the tab bonding board.

[Redwood]

Re: Samsung UN50J5200AFXZA - Screen goes blank

Would this be a case where renewing the tab bonds might feasibly fix it? I've never tried that but I've done a couple of Android phone screens. I've got appropriate heating equipment and a high quality FLIR camera.

Just going to need to clear a bit more bench space before I can separate the panel from the frame.

[budm]

Re: Samsung UN50J5200AFXZA - Screen goes blank

Would this be a case where renewing the tab bonds might feasibly fix it? I've never tried that but I've done a couple of Android phone screens. I've got appropriate heating equipment and a high quality FLIR camera.

Just going to need to clear a bit more bench space before I can separate the panel from the frame.

No.
See picture of the tab bonding board.

[Redwood]

Re: Samsung UN50J5200AFXZA - Screen goes blank

Not really clear what I'm looking at here. Is it just that the tab where it's bonded to the panel is sandwiched between parts so you can't get at it?

Soooo...TV's junk then?

[budm]

Re: Samsung UN50J5200AFXZA - Screen goes blank

You need to remove the metal frame around the LCD panel assembly to see the boards, otherwise there is nothing you can do, and if lets say you did find shorted SMD cap, you have tools to do SMD repair, right?
https://www.badcaps.net/forum/attach...6&d=1401307181

[Redwood]

Re: Samsung UN50J5200AFXZA - Screen goes blank

I am totally prepared to separate the frame, like I said I just need to clear a little space first.

I've never tried replacintg SMD caps but managed to do a couple of SMD microswitches on a laptop touchpad recently. I have a variety of soldering irons and a quality heat gun with nozzles.

I've probed most of the caps on that board and haven't found any with less than at least 0.7K ohms.

[budm]

Re: Samsung UN50J5200AFXZA - Screen goes blank

So you already took the frame out and get to the caps on the tab bonding board of the side that does not get pictures? None of the caps on that side of the board show <700 Ohms compared to the good side?
No sign of any corrosion from liquid either?
https://www.badcaps.net/forum/attach...0&d=1539189835
It looks like you can almost get to all the caps on the tab bonding boards without taking the frame off.

[Redwood]

Re: Samsung UN50J5200AFXZA - Screen goes blank

Well I have to admit this vocabulary is new to me here but I am assuming the tab bonding boards are those long narrow boards which are connected directly to the T-CON board, is that not correct?

If so, then yes, they are pretty much completely exposed along the bottom edge of the rear of the unit without pulling the frame. They have ribbon cables that do a 180° bend up under the frame and from there I can't see what's going on but I've been assuming those are fastened to directly to the panel.

[budm]

Re: Samsung UN50J5200AFXZA - Screen goes blank

Yes, they are the long skinny boards, the speakers are blocking part of the board too.
If you are lucky then it may be just bad caps with low resistance readings, if not it can be the embedded IC (small rectangular piece you can see in post 7) on the flexible board between the LCD glass panel and the tab bonding board.
Hoping for bad caps, hate to see 55" going to waste.

[Redwood]

Re: Samsung UN50J5200AFXZA - Screen goes blank

It's only 50", but still, yeah, a nice TV and with half of it working so we know the boards are all good it sure would be nice to put it back in service.

What would be the minimum resistance value that would tip me off to any bad caps?

[budm]

Re: Samsung UN50J5200AFXZA - Screen goes blank

If the caps show <100 Ohms the I would suspect them, since you have two tab bonding board, the layout is basically the same (may be mirrored image) which you can do the comparison readings.
Those MLCC (Muti Layer Ceramic Capacitor) when it goes bad it tends to show low leakage resistance.