Samsung UN55MU8000 - Backlight But No Picture Problem

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

I have never done this operation so be patient, i can't find E5 component's datasheet, but try to remove all of the ones on first photo.. i did not expect those values ..

[diif]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Photo #1 post #40, you're indicating ground incorrectly.

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Photo #1 post #40, you're indicating ground incorrectly.

Thank you Sir.

I corrected that (or shall I say I was corrected) a few posted down when @mmaven806 chimed in to lend his thoughts.

Davi.p suggests that I should remove a few diodes from the panel board but I was hoping to eliminate the mainboard before I started doing anything other than testing and probing. Not really sure if there is a way to do this without having a known working mainboard to reference...

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

are you an hobbist? rapairing at home is uncofortable but anyway statistically is much better to intervene first on panel's boards what do you think you can do with mainboard whithout a schematic?

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

are you an hobbist? rapairing at home is uncofortable but anyway statistically is much better to intervene first on panel's boards what do you think you can do with mainboard whithout a schematic?

100% a hobbyist working out of my garage late at night when the children are alseep!

Thank you for the pep talk.
You are 100% right about focusing on the panel given what we know and dont know.
I'll report my findings shortly.

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

are you an hobbist? rapairing at home is uncofortable but anyway statistically is much better to intervene first on panel's boards what do you think you can do with mainboard whithout a schematic?

I went in and removed the E5 components on the left side as you suggested.
Attached are the resistance readings at each pad. They have changed for sure but I dont know how to interpret the changes.

After taking resistance readings I connected the FFCs back and powered on the TV. No change. Black screen. I then removed the right FFC and left only the left one on and restarted. Still no change. Blank screen.

Let me know what you think!

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

have you removed the previously placed tape on 2pins?

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

have you removed the previously placed tape on 2pins?

No, thise pins remain covered.
Also those pins are on the right side FFC.
The E5 components are on the left side.

Akso worth noting these is no flex cable joining the 2 LCD panel boards together like younwould find on many TVs.
They only have 1 FFC each and that leads to the mainboard.

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

So this is strange, so you have fault on right side not left because protection doesn't take place with covered pins, and you have odd values on the left side diodes.. so it hadn't sense to remove left diodes, maybe the values on them are ok, in the truth components sometimes must be removed to make a valid measurements , now better to remove right side diodes or test other pins to cover..

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

So this is strange, so you have fault on right side not left because protection doesn't take place with covered pins, and you have odd values on the left side diodes.. so it hadn't sense to remove left diodes, maybe the values on them are ok, in the truth components sometimes must be removed to make a valid measurements , now better to remove right side diodes or test other pins to cover..

All the top leads of the 3 on the right are already reading open (rightly or wrongly) so I am wondering what would removing them accomplish?
If they were defective (failed open) then we would need to install replacements so see any change in behavior right?

Thank you for your patience in explaining it to me. Im still very inexperienced with display panel repair.

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

If i remember you already tried many pins to mask, there is not much to do with the panels, in some models diodes are connected to gnd by a couple of resistors that goes bad, but this is not an overload then so tv must not be in protection, try with diodes first, i must notice one thing, the first left photo shows a different section refers to last photo, why? when you say "open" what do you read in your multimeter?

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

If i remember you already tried many pins to mask, there is not much to do with the panels, in some models diodes are connected to gnd by a couple of resistors that goes bad, but this is not an overload then so tv must not be in protection, try with diodes first, i must notice one thing, the first left photo shows a different section refers to last photo, why? when you say "open" what do you read in your multimeter?

Thabk you for the reply and sorry for the confusion regarding the boards.
The left and right board are not identical. The left board has a set of ICs near the FFC connector that the right side does not.

Please see attached pics...

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Just wanted to do an update.
Being that this is my first foray into panel board repair I am 'still' a bit nervous about doing anything to it that I cant undo. The films are pretty delicate, the SMDs are very small and my experience in the theory of how these things work is severely lacking.

Im opting to verify that the issue (or main issue) isn't in the mainboard first before proceeding. I have ordered a mainboard from a reputable supplier and will test it against this TV set to see what the results are. If the issue is the mainboard then I will not have to proceed in dissecting and potentially ruining a good panel. If the panel is the problem then I will proceed with its repair knowing for certain that the issue lay before me and not somewhere else.
Luckily the supplier I am buying the board from has a generous return policy and I would only have to cover the shipping costs. I hope to have some answers by the end of the week and will keep you guys posted.

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

which board number have you followed?

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

which board number have you followed?

The mainboard number I ordered is Samsung BN94-11960A.

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Well i got a mainboard in today but after plugging it in I was disappointed to find that i still had no image on the screen. But what's worse, in addition to no video...there was no sound either. At least with my original mainboard you can hear the sound of you going to the Home menu and selecting different choices. This one had nothing. I put the original board back on just to ensure nothing changed and it hadnt. I have no picture BUT sound with that one. Both boards are the same part number and revision number.

I find it very hard to believe that the vendor (Shop Jimmy) sent me a defective board. When i get a chance i will take voltage readings and compare them to my board.

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

I went ahead and did some measurements before packing it up to send back.
The voltage readings were identical to the ones I described in Post #20 (only panel related voltage found was panel_3.3v and that was indeed 3.3v. AVDD, HAVDD and VGH were all 0 V.

I then went and checked the resistances across all the coils.

There were some notable differences. Particularly on the right side along the heat sink. On my original board they would fluctuate wildly but on this board whey were stable and within reason.

I don't know why this board will not allow me to access the OSD via the remote like my original board. It could be they have different firmware on it and behave differently to protection codes.

Once I replace the backlights I will try my board and, if necessary, order another one to test out.

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

You want to replace back lights?? Are you kidding?! So you have back lights working and you want to replace them too? And you bother about removing a simple little diodes? No, you're out of focus now.. removing the panel is much more dangerous than removing 2 diodes.. c'mon..

I add another possible source of fault: the spi flash on the panel's board, maybe you can try removing it, freezing, reading, programming again, the difficult is that is Qfn package, i don't know how you can handle it, maybe flying wires..

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

You want to replace back lights?? Are you kidding?! So you have back lights working and you want to replace them too? And you bother about removing a simple little diodes? No, you're out of focus now.. removing the panel is much more dangerous than removing 2 diodes.. c'mon..

I add another possible source of fault: the spi flash on the panel's board, maybe you can try removing it, freezing, reading, programming again, the difficult is that is Qfn package, i don't know how you can handle it, maybe flying wires..

Thank you very much @Davi.p. I have changed quite a few backlights and VERY confident doing so. The miniature scale of the panel board is what makes me nervous. One wrong move and you lose an SMD you desoldered and you'll never be able to find it again. Or maybe you cant identify what an SMD is... like that E5 diode we were looking at. I saved them bcos I have no idea how to get replacements!

Perhaps I should CHECK the backlights first before proceeding. I saw some dark spots and knew quite a few LEDs were out so my natural instinct is to eliminate it as a source of the problem.


I know nothing of the SPO flash on the panel board. Allow me to do some online research on what it is and how its repaired.

Thank you again my friend!

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

So now i will tell you something important.. as another (maybe the hundredth) time, this seem to be a proof of that panels (matrix controls, tcon and backlight) are destroyed by tension spikes, that can cause multiple damages, so your backlight is bad toghether with the fault at matrix electronics, sadly, so its a challenge repair both.. I dont suggest you starting with the less important / easier backlight, before you find the obscure one.. dont you agree? I will let you know that finding the panel's firmware will be almost impossible unless the magic Lotas comes in help.. have you got an hot air station? Truely it can be easier or safer to remove the diodes with stylus with a big blob of solder because them are tiny.. dont use flux that makes harder to join the sides with the blob.. 7 seconds job! And the tooth is removed..