Samsung UE32F5000 no Backlight

[o0larry0o]

Hi all,
I'm very new to this forum, so i'll try to be as clear as possible and respect the rules, please tell me if I do something wrong

I have a Samsung TV UE32F5000 (AW), the TV is approx 5 years old, and it's a second hand.

Last week on power on, the TV was flashing between dark screen for 1sec, and image for 1 sec.
I rebooted the TV and all went good.
Yesterday, the TV was behaving correctly, I went to the kitchen, in the meantime i guess the TV went into sleep mode .. and then I was unable to power it back on.

after doing some digging, and using a torch, my LCD panel is working, I see the Samsung logo when i power the TV, so my guess is that the backlight is dead ...

now, after reading carrefully :
https://www.badcaps.net/forum/showthread.php?t=44102
and
https://www.badcaps.net/forum/showthread.php?p=612335
and
https://www.badcaps.net/forum/showthread.php?t=51251

I understood the why and the hows

What i did:
------------
- open the back panel to check for any faulty capacitor

- from what I see, none of them present the visual of a faulty one (leaking etc.)
- the fuse shows 25ohms no idea if it's correct, but at least i know it's not dead

that's it ....

what i want to do, but not sure how:
----------------------------------------
- check the power output of the power board

- I read that i needed to plug the board, and check the current between the pin number 12 and the chassis

- how do i do that ? I have a multimeter, i'm not sure on which mode i should set it (please check the picture)

- if the power is ok, i need to check the LED strip for any faulty ones

- does anyone could provide me with a procedure for accessing the led strip ? I had a look, but i don't want to break anything, is there a video somewhere ?
- what's the difference between a "short" led and "open" one ?
- how do i set my multimeter to check the LEDs ?
- I have a decorative LED strip and its power supply (9V DC, 4A), can i use that to power the TV LED to check ? from what i've read I guess 9v DC will be too less to see anything

Many thanks for your help
Ludo

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

Update, I unplugged eveything.
Accessed to the LED
removed the mainboard
removed the TCOn board

Left in place the power board, plugged in the AC --> no light.

As i understood, in the configuration, the backlight should lit up because the main board is not connected, right ?
so it's either an open circuit, or a failling power board, right ?

if I understood well, a short LED would not give this situation, as some LED should lit up, right ?

many questions ...sorry

still then I need to be sure how to :
- check the power board output
- check the LED strip individually

could you guide me througt the step ?
thx

[budm]

Re: Samsung UE32F5000 no Backlight

BN44-00605A power supply/LED driver board.
With just the power supply board by itself, you need to check the DCV between the chassis GND and the LED connector pins:
+1, -1
+2, -2
+3. -3
+4, -4
Report what you get.
I will not be surprised if you have bad LEDs in the panel.
Pictures provided by shopjimmy.

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

thx
but i'm confused or i'm not understanding you correctly, you replied somewhere that to test the power supply, the LED strips must be connected. I understand the opposite from your answer.

and then if the LED cord must be connected (which seems to be logic to me since the LED are in Series) and the power set ON, how do I technicaly put my probes ?
I mean some heavy current runs in there, and you don't have access to the pin anymore, only way is to test from the back of the board ...

well i'm a bit scared to manipulate the board like that

on the other hand I've juste understood how to test the LED with my multimeter in diode mode, and one of them does not light up.
Since i'm confident by nature, i will guess that the power board is fine, and this LED is open resulting in nothing going on

does this sound logic to you ?

Anyway I will test the power board by itself first., but i don't know how to set up my multimeter, well i'm guessing i should be in DC mode and 200V ?

thx

[budm]

Re: Samsung UE32F5000 no Backlight

"but i'm confused or i'm not understanding you correctly, you replied somewhere that to test the power supply, the LED strips must be connected. I understand the opposite from your answer."
Right now I want to know what you get with the LED connector in place first, then we will take the readings without the LED connector in place.
You need to use small probe to check the DCV from the back side of the female connector.

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

I did it with the connector in place AND the led strip connected, and probed from the LED side

-1 : 180 / 200 V
+1 : 200 / 255 V
-2 : 160 / 180 V
+2 : 180 / 200 V
-3 : 140 / 160 V
+3 : 160 / 180 V
-4 : 0 V
+4 : 137 / 160 V

depending on what i tested some strips lit up, but 2 never did (on the same side), including the one with the faulty LED.

[budm]

Re: Samsung UE32F5000 no Backlight

OK, so you already took the LCD panel apart and get to test the LED strips and the LEDs .

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

yeah I needed to be reassured ... and then ..what the hell
the values seems good to you and consistent with an open strip ?

[budm]

Re: Samsung UE32F5000 no Backlight

-4 should not be 0V unless that strip has open circuit.
The LED strips are connected as one big long strip.
The +1 pin the Anode pin of the first LED string that gets the Boosted Voltage (Q9101 Inductor T9101, C9102) feeding it, the -4 is the Cathode return pin of the LED string which is connected to the Drain pin of the PWM controlled power MOSFET to maintain constant current through the LED string. the Source pin of the MOSFET is connected to the current sensing resistor R9110, the Voltage drops on the resistor is fed back to the FB pin of the LED controller IC to maintain the constant current, the other end of the resistor is connected to GND.

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

ok, great then, as I found the faulty LED i just need to replace it or replace the strip.

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

Hi all
final update to the thread, thx to everyone here I've order some new LED to replace the faulty one and my TV is up and running again.

again many thx to you

[budm]

Re: Samsung UE32F5000 no Backlight

Thanks for the follow-up.
So what and where did you order the LEDs from?

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

I bought pieces of led strip sold by someone from this forum on Ebay.
I did not wanted to unsolder and resolder the led like i saw, this method was way beyond my skills

[budm]

Re: Samsung UE32F5000 no Backlight

OK, you use the stacking method.
Just make sure to turn down the Backlights level in the on screen user menu to as low as possible to extend the life of the LEDs.

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

I did, the max on my TV is 20, it set it at 10, and frankly i don't see the difference I watched I show at noon with lot of sun, and it's okay.

Do you think half is enough or should I decrease it ?

[budm]

Re: Samsung UE32F5000 no Backlight

That is more than enough, or lower if the pictures quality is good enough for you in the bright room.

[flocko]

Re: Samsung UE32F5000 no Backlight

he sent me a photo of the failed LED and I custom made one for him to fit the limited space he had on the strip, and advised how to connect . I am all ways ready to help were I can. I have also added more lens types (5 types now) to cover most strips on my eBay listing and send to Europe and beyond Flocko

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

Ahh flocko, I couldn't find your user name on the forum :p
thx for your help, it works like a charm

[flocko]

Re: Samsung UE32F5000 no Backlight

Thanks glad to help.Even with very little room this has to be the better way to replace failed LEDs.

[o0larry0o]

Re: Samsung UE32F5000 no Backlight

I think so too, unless you have a spare strip to try to unsolder the led with a heatgun ..and fail ...