UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt fix!

[lotas]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

But, through the holes you can see that the backlight is on, or so it seems to me.

[EazyBone]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

But, through the holes you can see that the backlight is on, or so it seems to me.

Yes, this TV is put together correct and working properly now. Just showing working voltages and what led tester draws.

This may help the OP

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Eazybone i think you are confusing more.. i don't know where your input can help the op, you had different symptom, no p. board self test done..

[EazyBone]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Eazybone i think you are confusing more.. i don't know where your input can help the op, you had different symptom, no p. board self test done..

TBH I don't know why this isn't already figured out. Samsung lights come on when you disconnect main from PSU. They light up. And if they don't it's the backlight or the PSU. He replaced the PSU, and he has image. I'm actually surprised it went further then this has. It's the backlights lol

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

But why don't to come to conclusion after a test? Before dismantling a giant screen?

[EazyBone]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

But why don't to come to conclusion after a test? Before dismantling a giant screen?

Hopefully not taking this in wrong way lol but, isn't it confirmed? Two power supplies and literally everything else is working. He has an image and sound, so it's not panel or main board. He's getting two totally different voltage readings when testing the LEDs. There is only 2 strips one is reading 100 and one is reading 63. Mine both test evenly. At 150 which is all I was trying to show. If this is incorrect just disregard but I'm gonna follow and see what goes on here. I want to know the fix too!

And in fact I have different tv and have just been unhelpful lol I'll stop here my bad

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

I have also diagnosed bad leds, but with the risk of handling a 65" how can a 5 min. test be damaging?

[nomoresonys]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

You're doing fine EazyBone, we need more like you, that is people that can communicate in a manner that isn't RUDE and MEAN-SPIRITED, keep on helping and leaning.

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

You have a failing backlight led, The normal led supply is 192v@700ma When one of the led's fails the voltage is high due to no current so no voltage drop. Your led tester likely supplies about 10ma, those testers are ok for testing one led at a time.
With full current the bad led will go open.

this logic seems sound but i would expect that i would see the backlights flash somewhat...at least to as bright as my tester can make them before they would fail...but i see nothing at all. i will test again next time i am there to really be sure i dont see any flash or voltage drop even for an instant.

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Here's some pics and voltage. My board also says 143 volts 65 inch.

we seem to have different boards. are you sure its the same exact model number tv?
after reading everything thats been written here and thinking about it...i am definitely leaning towards bad backlights. i would just like to know some kind of more definitive test i could do before opening up the panel. it is quite a job!

the led tester giving uneven reading for one strip vs the other is definitely suspect. i would expect to see it the same on both sides. can we assume this for most tvs?

[nomoresonys]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

RJ explained it in post #7, there's your definitive answer.

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

triplefour why don't you follow advices instead of asking more? my test tooks more or less 10 minutes.. try..

[EazyBone]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

we seem to have different boards. are you sure its the same exact model number tv?
after reading everything thats been written here and thinking about it...i am definitely leaning towards bad backlights. i would just like to know some kind of more definitive test i could do before opening up the panel. it is quite a job!

the led tester giving uneven reading for one strip vs the other is definitely suspect. i would expect to see it the same on both sides. can we assume this for most tvs?

It's different. Was my mistake. My data is all wrong so disregard that sorry. I have RU model or something

Voltage is not the same on both sides all the time. I Google searched and that tv 5 big strips and 5 small strips which look like they connect together, so one side probably runs 3 and other runs 2.

Either way this is probably 95 percent backlights.. Samsungs are built to turn backlights on when main board is disconnected. So you know it's either power supply or lights. It should ALWAYS turn them on. But yours doesn't. It's either power board or lights. And your replaced power board. So it's definitely lights. In my opinion

And davi and rj gave you the tests to show that right

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

It's different. Was my mistake. My data is all wrong so disregard that sorry. I have RU model or something

Voltage is not the same on both sides all the time. I Google searched and that tv 5 big strips and 5 small strips which look like they connect together, so one side probably runs 3 and other runs 2.

Either way this is probably 95 percent backlights.. Samsungs are built to turn backlights on when main board is disconnected. So you know it's either power supply or lights. It should ALWAYS turn them on. But yours doesn't. It's either power board or lights. And your replaced power board. So it's definitely lights. In my opinion

And davi and rj gave you the tests to show that right

i see from ebay searches that the replacement backlights are 10 strips. each has 6 led on them. they look like broken up into two sets of 5 strips each....so i should expect same voltage to be shown by my tester. i am using this as my basis for suspecting the backlight (and that i replaced psu and still no backlight)
i am going to take this tv apart today and know for sure.

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

triplefour why don't you follow advices instead of asking more? my test tooks more or less 10 minutes.. try..

i just wanted to hear someones opinion on why i get no flash at all with the psu even tho the tester lights it up.
seems like i should at least see some flash or voltage drop. i will test this today for sure.

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

ANA-DIM is 0,08v so probably it is selected a very low brightness level not noticeable in a flash

[EazyBone]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Those 5 small strips connect to the 5 big strips essentially making 5 strips. 5 connections can't be split evenly so you will have a different voltage on each side. So no you shouldn't expect the same voltage if there is only 2 separate connectors coming from PSU. It should essentially look exactly like this picture. 5 rows with connections coming from one side only. And this picture is a great example because he also has a short in the LEDs. All light up except for that top right set. So it appears when using the LED tester that your lights are "fine" because you can't see them all. But the power supply knows there is an issue so it wouldn't light them up. And as RJ points out not enough amperage generally for the LED tester to cause the LED to fail. Mine has so far never failed me, but I have one that puts out 100ma.

[Diah]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

,,.

this photo not Samsung TV BL right ? hisense !!!

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Those 5 small strips connect to the 5 big strips essentially making 5 strips. 5 connections can't be split evenly so you will have a different voltage on each side. So no you shouldn't expect the same voltage if there is only 2 separate connectors coming from PSU. It should essentially look exactly like this picture. 5 rows with connections coming from one side only. And this picture is a great example because he also has a short in the LEDs. All light up except for that top right set. So it appears when using the LED tester that your lights are "fine" because you can't see them all. But the power supply knows there is an issue so it wouldn't light them up. And as RJ points out not enough amperage generally for the LED tester to cause the LED to fail. Mine has so far never failed me, but I have one that puts out 100ma.

i took apart the panel and found that indeed there are 5 long strips (each made from 2 strips) and they are wired such that 3 of the five are lit by pin 1 and 2 of the led connector and the other 2 are lit by pin 3 and 4. so the voltages i was seeing on my LED tester were about what i should expect to see. if i had known that i might not have taken apart the panel but its hard to see what configuration they have in there until you do that. i guess i could have deduced it from looking more closely and thinking about how they would have to split it. but this is besides the point. i tested each strip and found they all light up. i tested even each LED individually and they all light up fully and show 2.6v .... so i cant detect any problem in the backlights.
yet with both power supplies i get not even the slightest flash of backlight (surely i would see something, staring at the LEDS directly. and i see no voltage drop upon plugging power. just the 280v comes up and stays.

so i am still nowhere closer to figuring this out.
do i need a 100ma tester to actually find the bad LED?
did they send me a bad PSU? how can that be when the PSU seems to produce all required voltages...just wont send current to the BL!

oh and to top it all off, i put the whole thing back together and now it wont turn on like before where i had sound and picture but just no backlight. now the mainboard seems to not turn on. the LED flashes what seems to be blink code 5. the led flashes twice quick, five times in a row. pauses and repeats. it does this 3 times and then settles back to a solid red LED. i try turning on many times and get this same blink code. when i check voltage at LED connector i see none now. so with MB connected no voltage at LED connector (but other voltages present) and without MB connected i see the 280v open voltage across the led connector.

what could possibly be happening here?
are we absolutely positive that samsung has not changed things with these newer tvs? has anyone seen this exact model?

it seems like its detecting that im trying to fix it and purposely breaking more so i cant!

its not like i did anything to the MB that should cause it to change its operation. all i did was disassemble the panel and test the backlights which appear to be fine!

****FRUSTRATION****


edit: can you tell me which LED tester you have? i have been wanting to get a higher powered one for some time but unsure which to buy!

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

So you insist to not give me your attention.. well.. i know BL leds problems are many times strange ones.. in these ones your BL tester is useful like a poop on the living room table.. if you gave the chance to my test you maybe saw that with BL outputs at nominal power the circuit detected a small leakage of one or more leds, returning not the correct tension to the current sense circuit.. by adding some leds in series you are equilibrating that tension, 192v / 60leds = 3,2v each led, 3,2v x 0,7A = 2,25 W, so take a led bar with similar leds and do the rest.
Your tv has been hit by an overvoltage maybe, in this sit. sometimes faults comes out serially and delayed.. that led blinking code it is associated with varoius faults i have seen, one of them is a faulty PSB, it is capable of outputting correct standby tension but not the the on state tension to the main board so the software stops (main cpu not working), or it is the cpu itself with problems, or even the on state software..

you don't have mention how many wires comes out to the leds..