Samsung UE55MU6120K Boot loop with backlight no video

[fanaticgames]

Hi guys, I have a problem with this TV, if I detach the flat lvds this seems to work (clearly I don't see anything on the screen), I tried to detach 1 flat at a time and the defect is not there (but shouldn't you see at least the meta display? ?), so the problem is on the mainboard or on the display? Has anyone solved it somehow?

[nomoresonys]

Re: Samsung UE55MU6120K Boot loop with backlight no video

not understanding, what exactly are the symptoms?

[KYBOSH]

Re: Samsung UE55MU6120K Boot loop with backlight no video

Its either the mainboard... or display as you have surmised.

The 'easiest' way to determine which is which for certain is to get a verified good replacement mainboard and install it. if the TV works then its the mainboard.
The key here is to get a mainboard that is VERIFIED good.

Some of the ones you see on eBay cant be verified bcos they were pulled from TVs with damaged screens that actually never displayed a picture. The issue with those boards could be the screen, the mainboard or both. The seller will almost never verify the part before selling and just assume its good.

The harder way is to test voltages on the mainboard while in a sort of diagnostic mode. This is where you trick the mainboard to think it has a good display attached and it sends signals it normally would. Different mainboards have different ways to initiate this diagnostic test. Some are as easy as putting a jumper on easily accessible pins. Others require soldering different traces together.


But before you do this you may want to check your backlights. Often times they are 'kind of' bad. Good enough to light up but bad enough to trip a protection circuit on the mainboard.
You'd do this with a backlight tester but it 'may' require you to open up the panel and remove the display screen to get access to them.

Good luck

[Davi.p]

Re: Samsung UE55MU6120K Boot loop with backlight no video

meta?? Half, che meta?? :+)

1) how can you state that tv is boot looping? Backlight does on-off?
2) so detaching a flat b.l. stays on?

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

not understanding, what exactly are the symptoms?

the tv turns on, the screen stays black with the backlight on and restarts continuously after 3 seconds. If I remove the panel flats, the TV turns on regularly, I hear sounds, the remote control responds and everything seems to work

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

Its either the mainboard... or display as you have surmised.

The 'easiest' way to determine which is which for certain is to get a verified good replacement mainboard and install it. if the TV works then its the mainboard.
The key here is to get a mainboard that is VERIFIED good.

Some of the ones you see on eBay cant be verified bcos they were pulled from TVs with damaged screens that actually never displayed a picture. The issue with those boards could be the screen, the mainboard or both. The seller will almost never verify the part before selling and just assume its good.

The harder way is to test voltages on the mainboard while in a sort of diagnostic mode. This is where you trick the mainboard to think it has a good display attached and it sends signals it normally would. Different mainboards have different ways to initiate this diagnostic test. Some are as easy as putting a jumper on easily accessible pins. Others require soldering different traces together.


But before you do this you may want to check your backlights. Often times they are 'kind of' bad. Good enough to light up but bad enough to trip a protection circuit on the mainboard.
You'd do this with a backlight tester but it 'may' require you to open up the panel and remove the display screen to get access to them.

Good luck

if I unplug the cable between the motherboard and the power supply, the LEDs stay on without problems even for 15 minutes, if they were faulty they didn't light up at all or not?

my question is if I test it with scotch tape by eliminating some clock signal lines, can I figure out if it's a display or motherboard problem?

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

meta?? Half, che meta?? :+)

1) how can you state that tv is boot looping? Backlight does on-off?
2) so detaching a flat b.l. stays on?

Sorry, yes half display :-)

1) yes, the backlight turns on and off because the tv restarts, you can tell by the red status led

2) if I disconnect the 12 pin cable that goes to the motherboard the backlight stays on without problems

[Davi.p]

Re: Samsung UE55MU6120K Boot loop with backlight no video

ok so panel problem mostly, check on the screen's small large boards if there's a short on the caps

[zwarder]

Re: Samsung UE55MU6120K Boot loop with backlight no video

try blocking ckv lines, worked for me

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

try blocking ckv lines, worked for me

I can't identify the ckv lines on this model, can you help me?

I can't connect the tracks to the serigraphs

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

ok so panel problem mostly, check on the screen's small large boards if there's a short on the caps

do you mean on the two pcb right and left in the panel?

[Davi.p]

Re: Samsung UE55MU6120K Boot loop with backlight no video

yep

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

yep

Nope, I didn't find any shorted capacitors

[Davi.p]

Re: Samsung UE55MU6120K Boot loop with backlight no video

locate on the panel connector if it is present a 1,8/3,3v

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

locate on the panel connector if it is present a 1,8/3,3v

yes I checked the winbond chip on the left pcb and there is 3.3V

I did some random tests with tape on the panel flats and the TV doesn't restart anymore and you can hear the audio and the backlight works but the screen is completely black, no image

[Davi.p]

Re: Samsung UE55MU6120K Boot loop with backlight no video

inject 12v on the 15v line, prepare to remove it when you see something wrong, better if you increase current slowly..

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

inject 12v on the 15v line, prepare to remove it when you see something wrong, better if you increase current slowly..

are we talking about giving current to the panel? and where I find the 15v line I have no diagrams and nothing is indicated on the pcb

[Davi.p]

Re: Samsung UE55MU6120K Boot loop with backlight no video

Ah, yes, try switching normally on the tv, if you can locate a 15 v for a short time on the capacitors on the screen's boards then you have located the 15v on those condensers, if the voltages does not appear then you must search for technical document of the model, or study the circuit on mainbboard , if you can't i need very sharp picture of it.

[fanaticgames]

Re: Samsung UE55MU6120K Boot loop with backlight no video

Ah, yes, try switching normally on the tv, if you can locate a 15 v for a short time on the capacitors on the screen's boards then you have located the 15v on those condensers, if the voltages does not appear then you must search for technical document of the model, or study the circuit on mainbboard , if you can't i need very sharp picture of it.

Left and right board photo:

[lotas]

Re: Samsung UE55MU6120K Boot loop with backlight no video

Do not try to supply 12v anywhere, otherwise you will completely kill your panel and motherboard! Check with a multimeter for resistance these leads on the protective diode assemblies relative to gnd.