Samsung UE55MU6120KXXU, new main board, no picture.

[Braderz]

Hi guys, am looking for some assistance here as I'm not sure on my next steps.

I got hold of the above mentioned TV and found that I had a probable fault with the main board, so I ordered a new one (with the exact same BN numbers etc) and have found slightly differing results between old and new. It seems as though it may not be a main board fault after all though, but that's where I need help.

With the old board in and everything plugged in, just get back light on, and I can hear the interface sounds when I press menu/hub etc. With the new board, with everything plugged in, back-light comes on for a few seconds then the TV cycles off, with one more flicker of the back light. However, when I unplug one of the two tcon ribbons, I get the back light stay on and I again can hear menu sounds, although this time only with the up or down arrows (I assume it's in setup menu or something)

Could it be that there is a seperate issue with perhaps one of the small panel boards? Or perhaps the original owner changed the board with a wrong version, and I've ordered the same. Is there a way to confirm the correct board required to suit this specific model?

Any help would be greatly appreciated. Thanks.

[dick_barton]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Some photos of your boards and interconnections could prove useful.

[Braderz]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Current

Small panel boards

Main board serial

[Braderz]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Current
https://ibb.co/9q8RXBZ
Small panel boards
https://ibb.co/CWjzWVJ
Main board serial
https://ibb.co/Hr2S7DG

[dick_barton]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Hi BraderZ,
Could you add your photos as attachments to you post. That way they stay on the thread for others who at a later date may have a problem with the same mode.
I can't even get them to load from the web address above.

Use "Go Advanced" and then add your photos.

[Braderz]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Think I've worked out how to do it now. Is there a way I can edit the OP and add them to that?

[dick_barton]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Is your power supply BN44-00807F and if so can you provide a close up of the connectors and legends marked by the red boxes.

If you disconnect one of the ribbons cables from the mainboard going to the panel, do you have half a picture. If not reconnect the ribbon and disconnect the second ribbon and check again. Take care not to damage any of the ribbon connectors.

[Braderz]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Yes that's my board. I've attached 2 pictures of each connection. I did notice ced that one of the pin holes has what seems like a potential burn mark on it. It's very faint you; can just make it out in the picture. (accross the top of the white plug)

Regarding the ribbons, no I do not have half a picture. Funnily enough it's only when I remove one of the ribbons that I get the back light come on. And that's when I can press menu buttons etc and hear the tones. When I press exit from the menu, for example, the back light turns down, almost like its responding appropriately.
I've just confirmed this on both boards. With both ribbons plugged in, it goes back into standby after a few seconds, but if either of them are removed, it let's me engage via the remote etc but as I say, it's blank, but with back-light.

[dick_barton]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

It looks as though that connector with the burnt pin goes off to the led strips. I would disconnect it at both ends and check the resistance is zero for each wire including the burnt pin. It looks as though your led strip has been taking too much current so I would be checking that there are no shorted led(s).

How bad is the pin in the connector that it plugs into

[Braderz]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

The pin itself looks good. I shall check the resistance shortly and report. Does this go off to the LEDs for the back light?

[Questcom]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

with power lead unplugged, try holding the toggle switch bottom right and plug the power lead back in, keep toggle switch held, it should hopefully come back to life

I had one that was doing the same and this sorted it

[Braderz]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Hi Questcom, thanks for the suggestion but I have just tried this a few times with each board in and it didn't seem to respond to the operation at all and continued its loop. Tried it with one of the flat ribbons removed as well.
Cheers anyway.

@Dick_barton, I have measured resistance for all 4 wires in that connector and got a perfect 00.00 each time.
Also attached a pic of the connection on the burnt end but looks fine.

Appreciate your assistance thus far by the way 👍

[dick_barton]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

How are the solder joints on the underside of that connector?

[nomoresonys]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Some tcon voltage testing: https://www.youtube.com/watch?v=r2a6LO1U3zU

[nomoresonys]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Another there, tracing down the short, checking the caps on tcon and driver board for shorts: https://www.youtube.com/watch?v=jLd6QO7Z7m4

[Diah]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

the big cheat Jock from Samy this TVs with Build IN T-CON and called ( screw free TV ), this one not much different from 2021 TU 6000 & 7000 series. Panel easy to crack from the rand, or get defect, reason always for cheap plastic bezel hold the panel in place.. if you remove the bezel you may see visible issue at LCD rand ( be careful if bezel removed never flip or let the set standing..LCD will falling out ) . i just scraped 2 set TU 75 from 6000 & 7000 series. they had same issue you mentioned. who need parts welcome.

[nomoresonys]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

Crap, my bad, those 2 posts were meant for a different thread.

[Braderz]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

@dick_barton I have attached a picture. On the power board I noticed an arrow stating 210v at this pin. I tested and only found 60v.

However, it's no longer doing what it was. Now the standby light just blinks and there is no back-light turning on. I'm not sure if ive shorted something while testing, but I doubt it. The pins on the other side of that connector are barely exposed so i couldn't have gone accross 2 points at once.
The only other thing I checked was the panel boards, which is obviously quite difficult due to the size. To be honest I didn't know what I was looking for. Wasn't really getting anything above 1vdc

It's not until @Diah mentioned this being a built in tcon board that this finally made sense to me. I was wondering how I could test that.
DIAH, I can't see any damage to the screen. Is it still possible to have a bad panel? When the back light is on, no signs of physical damage..

[dick_barton]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

There looks like two sets of leds. When you power up what is the peak voltage at the connector. It may peak quickly at switch on and then drop to 60V you mention.

If you disconnect the main board from the power supply and switch on do the backlights come on?

Can you post photo of the connector with the associated legend

With the old board back in do you still just get the backlights on as in post #1?

[Diah]

Re: Samsung UE55MU6120KXXU, new main board, no picture.

It's not until @Diah mentioned this being a built in tcon board that this finally made sense to me. I was wondering how I could test that.
DIAH, I can't see any damage to the screen. Is it still possible to have a bad panel? When the back light is on, no signs of physical damage..

the answer YES & NO. you need to do exact testing one by one and report the result.

you have 2 groups of LED back light.. we need to know if there issue..

1- disconnect the main boards from the power boards. set your digital meter on 200V DC, put the black probe on the chassis and the red one at each +1 & +2 at the LED back light socket. do it one at time, after you power it on ( plug it in wall socket ) read the voltage how its go high and low when the LEDs come on. write here your reading.

( if you look at the BL sockets, the first pin at top line which close to the panel are +2 and the next at down line -2, then next wire at top line +1 and the next down line -1)

2- next at same way ( main boards remain disconnected ) you need to read the voltage direct on +1 & -1 and then +2 & -2

remember each test you need to do it when the set plugged in wall socket. ( dont do the test white set remain on to avoid confused at reading )