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

[triplefour]

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..

sorry i did not mean to ignore you. this test you speak of is a valid one. if i had the spare LED bars with correct number of LEDS and the same voltage LED's i would try this but i am doing this far from my home so dont have all my spare parts with me. i will definitely have a look around when i get back home and try this. i still dont hear a solid explanation here as to why i wont at least see a little flash as the PSU "tries" to power the backlight before "realizing" it has some problem once the power reaches a certain level? or could it do all this without any LED reaching the required voltage to produce even faint light?

a higher powered LED tester, or suitable replacement strips would tell me much more but i work with what i have for now...

oscilloscope would be nice too but i still havent got my hands on one

and i thought i did mention there are 4 pins that are connected from the PSU to the backlight circuit.
there are many unconnected pins but i am ignoring them and just calling 1-4 the ones that are connected.
pin 2 and 3 are linked together via trace on PSU.
with LED tester (10ma)
positive voltage to pin1 and negative voltage to pin2 gives 100v to 3 of the strips
positive voltage to pin 3 and negative voltage to pin 4 gives 64v to the remaining 2 strips.
they can be seen to be lit up with no problems but as you and others have mentioned, with only 10ma low current LED tester i may be getting a false positive here.

it can be hard to understand. after reading your post again im not sure i even understand what test you wanted me to do. add LEDS in series? how many to add? how to add them? sounds very complicated. i could see soldering some wires from the 4 pins of the LED to a similar though different set of LED strips with the same voltage and number of LED's but beyond that i cant see...???

edit: after reading your posts again! i see what you mean... you can add some LED's in series with the return line to make up for some that might be failing. its worth trying.
if it is failing after a certain current (past 10ma) maybe it is failing as a closed short instead of open. in that case the extra LED's would make up for it. if it fails open though this wont help im guessing.

[triplefour]

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

the seller has responded to my message.
my original message was before i took the panel apart. i simply said that i tested the backlights with my LED tester and they appeared ok but the PSU wont power them without the main connected.
he replied one sentence. saying i most likely have a mainboard issue. either he is unaware of the samsung power on self test, or hes bullshitting me, or he has intimate knowledge of this tv and knows that samsung has done something different here and the mainboard is involved in telling the PSU to power the backlights and the PSU cant power them otherwise.... my money is on that he just has no idea and doesnt want to believe he could have sent me a bad PSU...and my money is also on that he didnt send me a bad PSU. just thought id mention how he chose to respond.
he has many more of them. and they are only 20$ but he doesnt appear to want to send me another one for free if he can help it!

please forgive my paranoia in that i keep coming back to this suspicion that samsung would remove this very useful feature from us to keep us from fixing tvs! but i have been seeing WAY too many samsung TV's more than any other brand and they are all under 3 years old. some of them only 1 year old. mostly i have been seeing panel faults but i know there was one that was like this as well where i replaced the PSU and the backlight and still couldnt get the power on self test to work! i never got to figure out what that problem was because the owner got fed up and called it all off.
edit: i looked it up in my notes and the model of that "TV FROM HELL" was UN65TU8000
that one DID have obviously blown out LEDs though. many burned LED's. we got replacement strips and they all showed fine with my tester like now, but the PSU wouldnt power them. so we got a replacement PSU and it STILL wouldnt power them. i was scratching my head and the customer lost his. it was a bad day id like never to repeat.

[nomoresonys]

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

So unplug cable from powerboard to mainboard and test these voltages, what are they? 2 ANA_DIM 0.08V
4 NC 0V
6 BLU_PWM 3.25V
8 PWR 3.93V
10 GND 0V
12 GND 0V
------------------------------------
1 GND 0V
3 A13V 13V
5 A13V 13V
7 A13V 13V
9 A13V 13V
11 GND 0V

[triplefour]

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

So unplug cable from powerboard to mainboard and test these voltages, what are they? 2 ANA_DIM 0.08V
4 NC 0V
6 BLU_PWM 3.25V
8 PWR 3.93V
10 GND 0V
12 GND 0V
------------------------------------
1 GND 0V
3 A13V 13V
5 A13V 13V
7 A13V 13V
9 A13V 13V
11 GND 0V

i dont understand your question... yes these are the voltages i have stated and these are the voltages i still get with mb unplugged. BL connected. PSU plugged in to AC.
i get 280v across the LED output as well. which is basically open voltage no current flowing. i should expect to see it drop to around 190v if the BL were consuming current.
please tell me if i have an error in my thinking!
thank you for all your help. everyone who posts even if it doesnt help i still appreciate it!

i only come here with the hard problems. the easy ones have been fixed already!

[Davi.p]

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

i try to explain again..
take a very small flat screw driver and extract the single connector of the wire of pin 4 from the connector holder (the return wire, since pin 2,3 are tied it is the same as if were 2 wires, it is 1 channel PS), take a known good leds bar, 6 leds on it are enough, also 3 can be enough maybe, if that has no test pads between leds create some by scratch it, now solder a wire on the input connector of this bar and connect the return wire to the first test pad after the first led , blocking it with tape or better an iron wire tie, if BL of the tv comes on you have some bad leds.. if no BL then try yo put the wire after 2 leds, 3leds.. and so on.. and sorry 4 my english..

[triplefour]

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

i try to explain again..
take a very small flat screw driver and extract the single connector of the wire of pin 4 from the connector holder (the return wire, since pin 2,3 are tied it is the same as if were 2 wires, it is 1 channel PS), take a known good leds bar, 6 leds on it are enough, also 3 can be enough maybe, if that has no test pads between leds create some by scratch it, now solder a wire on the input connector, and connect the return wire to the first test pad after the first led , blocking it with tape or better an iron wire tie, if BL of the tv comes on you have some bad leds.. and sorry 4 my english..

i did understand you eventually. thank you. i will try this when i can. in this case there is no pin that can be taken out. its the socket style that just clips in. no screws in this tv at all either! i would have to do something pretty destructive maybe to insert my LEDS here... ill think about it more.
well i guess it could be done if i kept the PSU disconnected from the BL socket and then soldered wires from PSU connector positive to positive, negative to one side of LED bar with 1-6 LED, and then other side of LED bar and then back to negative

is there no risk here in adding more LEDS because the worst that can happen is the PSU overcurrent protection shuts it down?

[Davi.p]

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

ah ok, no wires, this is somewhat a big problem, i haven't noticed

[triplefour]

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

ah ok, no wires, this is somewhat a big problem, i haven't noticed

yes they are cutting costs wherever they can. and the tvs seem to always be panel or backlight failure with no reason why just one day they go to turn on the tv and its a black screen. easy board swaps to fix tv's are a blessing we see less and less of these days

is there any device like a load tester that can simulate an LED string of any length and voltage? this would be a nice tool to test the current output of the LED driver of the PSU without needing to use any backlight strips.

[Davi.p]

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

you could get a wire with faston connector for the board and a tinned end wire to insert in the panel socket, only wire 1,4 are needed

[triplefour]

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

you could get a wire with faston connector for the board and a tinned end wire to insert in the panel socket, only wire 1,4 are needed

yes there are ways to rig this up for sure. and im sure ill try this if not on this tv then on another one. but now im thinking even though i get the 100ma tester, i still could have this problem occur...just if it occurs after 100ma...700ma is quite a lot more than 10ma...i dont think i was appreciating just how weak my little tester is! and my bench PSU can only do 30v5a so ....
for 200$ i could get this one... https://www.amazon.com/NICE-POWER-Va...0C7ZXYGHM?th=1
which can do 200v1A

would this be a useful tool for testing backlights to the full brightness?

sooo...if you rigged up some LED's like this hanging out in the back of the TV, could you then "repair" the backlight and use the TV like this without actually changing the strip? like...without opening the panel! you would have a couple missing LEDS so maybe some dark spots but would this work long term as a ghetto fix? block the LED's with some tape so they cant be seen shining out the back of the tv? am i dreaming?

[EazyBone]

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

Is there one specific LED that turns on much slower then the others? The tester I use is a Sid kt4h and it puts 100 ma to LED if needed. Not sure if that'd be enough to fail.

I literally took apart a TV tonight looking for a bad LED. The tester showed open. I put it down each strip and found one that didn't light up. I went in series on the strip, lighting up 1 then 2 together and found led 4 was bad. I popped the magnify cap or whatever off. Took the LED tester to both sides, it fluttered and lit up. I tested the strip again, now they ALL lit up. Thinking it was a mistake I went over every single LED strip again. Now everything lit up. I literally did nothing but they all lit up. But I still changed that particular led because I'm sure it was the problem. Just because it lights up don't mean it ain't a problem. I'd say most don't have a extra strip to do davis test, but I still thinks it's your backlights. You have 2 psbs outputting exact voltage necessary but won't turn lights on.

Still following to see if there is an answer lol

[EazyBone]

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

Just found this amazing item on AliExpress. Check it out! $25.02 23%OFF | LED Strip SVC650AG6_R L BN96-50313A BN96-50314A For Sams ung UN65TU8000 UN65TU8200 UN65TU7000 UE65TU7105 UE65TU8000 UE65TU7000
https://a.aliexpress.com/_m0Ka1Fk

$25 off ali express. I think it'd be cheaper to just buy them lol

[triplefour]

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

Just found this amazing item on AliExpress. Check it out! $25.02 23%OFF | LED Strip SVC650AG6_R L BN96-50313A BN96-50314A For Sams ung UN65TU8000 UN65TU8200 UN65TU7000 UE65TU7105 UE65TU8000 UE65TU7000
https://a.aliexpress.com/_m0Ka1Fk

$25 off ali express. I think it'd be cheaper to just buy them lol

something wrong with that url i think... and i still cant really be sure whether i have bad backlights or if i was sent a bad PSU...
im thinking i need something that can test the backlights with more current,
or to do like davi.p is saying and try and add some LED's in series,
or wire up some salvage strips of comparable voltage and number...
maybe buy another PSU...(please...anything but this!)

[triplefour]

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

https://www.badcaps.net/forum/showpo...0&postcount=15
so i just realized that this tool i bought a while back (but still havent really figured out how to use) has a LED backlight driver in it that seems to claim to do 120ma ... and after looking at my cheapo tester and trying to figure out what ma it outputs at i really cant say. but it looks like similar looking and priced ones on ebay output about 35-50ma ... im not sure where i got the 10ma number from. the thing is though this LCD panel tester came with all kinds of wires and even some nice probes that would be handy to use for the LED backlight driver but for its output there is a 4 pin connector for which they have given me no adapter to plug the probes into. always something...gotta craft something to make it work!

[nomoresonys]

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

i dont understand your question... yes these are the voltages i have stated and these are the voltages i still get with mb unplugged. BL connected. PSU plugged in to AC.
i get 280v across the LED output as well. which is basically open voltage no current flowing. i should expect to see it drop to around 190v if the BL were consuming current.
please tell me if i have an error in my thinking!
thank you for all your help. everyone who posts even if it doesnt help i still appreciate it!

i only come here with the hard problems. the easy ones have been fixed already!

Ok, so you have the bl-on and the ps-on, that shows that YES this tv should light up the backlights with cable from powerboard to mainboard unhooked, there's a possibility that the problem is in a connection of the backlight circuit and not necessarily an led.

[nomoresonys]

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

You prolly should have checked for high resistance in the backlight connections while you had it stripped down.

[triplefour]

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

You prolly should have checked for high resistance in the backlight connections while you had it stripped down.

yes i also thought of this as i drove home with the tv in my car... dang it!
ill probably end up taking it apart again
the thing is because of its socketed design, and the way they put the backlights and the paper over the spot you need to get to, i would have had to take all the backlights out to even get to where the socket makes connection with the strips...or theres probably some other easy way that ill have to figure out when im back in there. i have the tv now so i can take my time with it.

but then again if there was high resistance in that connection, wouldnt my weak tester not even be able to light things up at all?

i reported before that i was getting 100v between pin1 and 2, and 64v between pin 3 and 4 with my LED tester but when i tested it at home i am reading 96.8v with a slight wavering to 96.7v and 63.9v with a slight wavering to 63.8v. not sure if they should be rock solid but they dont waver much. anyway the math checks out: 96.8v/36 LEDS = 2.68v per LED which when i was testing them individually most of them read at 2.6 ... just a few read at 2.7
and 63.8/24=2.65 which again seems about right.

im on the quest to power them with more amps and see if something craps out.
or to find comparable strips and rig them up.
or insert a few extra LEDS in series as per davi.p suggestion.
and/or test resistance in the connection between backlight strips and the socket that connects to the PSU.
im not trying to buy new strips or another PSU before i figure out for sure whats wrong.

[nomoresonys]

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

I'm prolly completely wrong with that guess, it's probably that your tester isn't putting out enough current to trigger the bad led so they light up, I don't really know what else would make it test at 280 instead of 192.

[triplefour]

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

I'm prolly completely wrong with that guess, it's probably that your tester isn't putting out enough current to trigger the bad led so they light up, I don't really know what else would make it test at 280 instead of 192.

yes im leaning more and more towards this as well. which is why im dreaming of getting a more powerful LED tester.

this one included in the panel tester says it outputs 120ma but it also seems to say it only outputs 30v...which would be pretty useless for any big tv...guess is its included for testing small monitors tvs or laptop screens.

i updated the thread with translated images of the panel tester. seems a useful tool if i ever find a use for it!
https://www.badcaps.net/forum/showpo...0&postcount=18

[triplefour]

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

can anyone recommend a more powerful LED tester? this one seems like a good deal at 50$ for claiming 150ma and it has adjustable outputs as well. do we believe it works as advertised?
https://www.ebay.com/itm/174949839584