Samsung UE32EH5000 backlight issue fix

[electrocuted]

+1 you guys are time and effort savers! Replaced cm867 with a 120μF/200V which was available and works fine. No external leak or bulge and positive leg cut as in the first pictures.

[CvendaCZ]

Re: Samsung UE32EH5000 backlight issue fix

Iam glad Ive found this post, because it seems like this is my issue too. My capacitor is just slightly bulged, and I can measure 235-255V on backlight connector (160V when I disconenct the main board). The backlight in my case always blink on power up, and even tho I havent tested the LEDs, I can see that all of them blink. I really hope that the only problem is just this cap.

[alfatv]

Re: Samsung UE32EH5000 backlight issue fix

It should be possible to check caps with a scope without removing them. You should see large spikes instead of relatively flat DC.

[Janysek]

Re: Samsung UE32EH5000 backlight issue fix

Dannyx Good job thank you

[brianbelfast]

Re: Samsung UE32EH5000 backlight issue fix

Thanks Dannyx from me also. Fastest Samsung "No Backlight" repair ever. Much appreciated.

[nomoresonys]

Re: Samsung UE32EH5000 backlight issue fix

I like those detailed posts Dannyyx, very helpful and informative.

[nomoresonys]

Re: Samsung UE32EH5000 backlight issue fix

I would go higher in voltage like 200 to 250 or so, same uf as previous cap just higher voltage.

[aaronwt6]

Re: Samsung UE32EH5000 backlight issue fix

The 40" EH series have the same issue as well. Different power supply but exactly the same failure. I've fixed several. Some with bulged capacitors and others that weren't so obvious. I don't have the numbers handy but just a heads up to everyone.

[fliperek]

Re: Samsung UE32EH5000 backlight issue fix

I have the same problem in my BN44-00493B, capacitor defect

[Dannyx]

Re: Samsung UE32EH5000 backlight issue fix

Barely a week after I fixed the last one, another one came in with the same exact issue, though this one broke the rule of not showing visible signs, since the cap WAS bulging, making the task much easier.

I can imagine all of these tellies came from the same generation and have approximately the same number of on hours, which might explain why everybody who bought them experienced failures at roughly the same time.....just a hunch.

[Dannyx]

Re: Samsung UE32EH5000 backlight issue fix

Even as a beginner, I didn't crack a single screen and haven't had any unfortunate events so far. Mentally prepared is right, because the first time doing I was very careful and mindful throughout the whole procedure, then gaining more and more experience and fixing more and more of them, I gradually started doing it faster and faster, applying maybe a little bit more "force" with each one I did

Panels ARE fragile indeed and the bigger the TV is, the harder the task, but unless you mess really bad, you should be able to get it out of there in one go and in one piece. They're not THAT paper-thin. Some tips if you haven't done this before, though some may vary depending on the TV:

-once you get the bezel off, you'll want to release the buffer(s) board(s) so they hang freely off the edge. Most just pop off with a bit of encouraging, but check fro screws first (though I've never encountered screwed-on buffers on Sammies so far). You don't want the buffers to get left behind once you try pulling the panel away because they can strain the COF (chip-on-flex) cables (the ones running from the buffer to the panel).

-remove the panel alongwith the supporting frame underneath it, instead of doing them separately. This way, when you place the panel down, it will be kept some distance away from the surface you're laying it on and stop dust and dirt from contacting the underside. The frame is held in place with clips on all sides. Be extra careful around the ones at the bottom because they're right underneath the COF cables and if you try using a tool like a screwdriver to release them, there's a possibility it will slip and poke a hole right through the COF! VERY bad and unlucky scenario.

-lastly, the reflector sheets under the panel. This is where you no longer have to worry about doing surgical work, since the panel is off. Grab and remove all the reflectors at the same time and lay them flat in that order. Don't pull them out one by one - no need to go through all that trouble, plus you risk getting gunk stuck in between them, which often happens no matter how careful you think you are. They have a nasty habit of slipping and sliding around....not much advice I can give you here other than press them flat against each other to keep as much air from getting between as possible.

Another thing about reusing LEDs: unless you have fairly good soldering skills and a good soldering iron/hot-air station, it's not going to be easy to pull LEDs off of a good strip without destroying them - I can tell you that much. They melt very easily, especially since they'd have to undergo TWO rounds of soldering: one to remove them from the good strip and the other to hopefully solder them back onto the faulty one. Of course, there's the infamous "stacking method" which involves chopping an entire working portion from a good strip and placing it on top of the dead LED with jumper wires, but I don't really favor that and don't regard it as particularly professional either.....go ahead and hate on me Good luck and let us know how it goes.

[vinceroger69]

Re: Samsung UE32EH5000 backlight issue fix

Thank you for all of that! It's very helpful and informative. Now I actually understand what's going on and why.

I'm going to start mentally preparing myself for the task of pulling apart the panel. Free or not, I really like the tv and I don't want to break it! But, IF I can salvage the individual leds from my already cracked vizio first, that should be good practice.

just check the vizio leds are the same voltage as some tv sets use 3v or 6v leds

[x_orange90_x]

Re: Samsung UE32EH5000 backlight issue fix

Thank you for all of that! It's very helpful and informative. Now I actually understand what's going on and why.

I'm going to start mentally preparing myself for the task of pulling apart the panel. Free or not, I really like the tv and I don't want to break it! But, IF I can salvage the individual leds from my already cracked vizio first, that should be good practice.

[Dannyx]

Re: Samsung UE32EH5000 backlight issue fix

Don't worry. I don't have a degree in electronics either - quite the opposite field in fact (translation ) - and I slowly learned stuff myself from scratch and from the internet. Blew up some stuff, got electrocuted a couple of times.....the usual stuff, whatcha gonna do ?

Now back to the matter at hand: the key word here is current, not so much voltage. LED drivers in TVs are constant-current (CC) supplies, meaning that they try to maintain a...well, constant current across a load (the LED strips in this case) regardless of its resistance.

The "resistance" (actually forward voltage in the case of diodes so LEDs also, but let's call it resistance for now) of LEDs drifts heavily with temperature, so as time passes and the LED gets hotter, the resistance decreases and current through it increases, because Ohm's law tells us that V/R=I. Where V is the voltage, R is the resistance and I is the current. So if we imagine V remains constant and R begins to drop, then I naturally goes up. If there's nothing to stop the current from exceeding a certain acceptable threshold for a particular LED/LED strip, the LED burns itself out.

So how can we limit I ? Well we can't modify R in the equation, because that's proprietary to the LED and there's no way to affect it without adding resistors for each LED which would be wasteful, however we can "trim" down V, so if NOW R drops AND V drops also proportionally, I no longer skyrockets to destructive levels. I won't go into too much detail as to HOW the PSU actually does this for now, but we can now put what we've "learned" into perspective: the PSU has a preset current it's trying to reach, tailored to the strips inside the TV (this also explains why not all PSUs necessarily work on all strips, even if the connectors matched or you try botching them in there). If everything's functioning as it should, the LED strips will reach this preset current and the PSU will stay on. If however the load is not connected (or "open-circuit" as we call it), the PSU keeps increasing the voltage in hopes that it eventually "sees" that current it expects, but with one or more open LEDs, there's no way it can reach it, so it goes all the way up to maximum briefly before "giving up" and dropping back down.

LED strips are typically in series, so if just one LED dies, the entire circuit is broken - simple basic stuff. I DID however encounter a particular type of Samsung which has two separate outputs from the power supply, each powering two strips, so what happens here is only ONE half of the screen will be dark, while the circuit running the other half will operate normally.

The problem can also work the other way around: if there's a SHORT and the current is too HIGH now, the supply may also shut down to prevent damaging components on the PSU itself this time.

Bottom line, you need to start looking for dead LEDs. PSUs rarely go bad, despite this particular scenario which has occurred several times now - doesn't necessarily mean it applies to you as well. I too had to take apart the panel to check the LEDs - it's the only way.

Of course, I don't claim to know anything, so if there's any error or bogus information above, feel free to correct me - it's just what I know and what I can share to the best of my abilities. There's people out there who are MUCH more advanced than me, no question about it...

Good luck and have fun

[budm]

Re: Samsung UE32EH5000 backlight issue fix

As I already explain to you, you have 400V feeding the LED Anode because the power supply is not seeing the load (open circuit) which is also shown in the link I provided to you. So what else do you want me to tell you, you have open circuit I.E open circuit of the LED itself or open circuit of the connectors that links the LED strip together, etc.
"Furthermore, you say things like "400v FEEDING" which implies the problem exists in the supply of electricity, not the destination.", Go buy a new power supply then if you think it is not the destination.
"Rather than explaining to me why that was irrelevant"
Do you want me to teach you the electronics class and explain every thing in details for you on exactly how the power supply and the LED driver circuit function? How many years do you want to spend YORU time and MY TIMES teaching you?

Post #8: "

425V!, you have open circuit in the LED circuit some where, will not be surprised if you have bad LEDs!
Look at the Voltage chart with load, it is supposed to be 297V 410mA.

How much more do you want to keep on telling you after that?

Yeah, I didn't notice the models were slightly different, but reading his post, I too would concur there's a dead LED somewhere - get to crackin' that sucker open, I'm afraid

[x_orange90_x]

Re: Samsung UE32EH5000 backlight issue fix

So far he is not convinced that he has problem with LEDs or open circuit, so I do not want to waste my time on that thread any more.

You speak to me as if I'm on the same technical understanding as you. I found it interesting that the voltage dropped when I unplugged and plugged back in the main board. Rather than explaining to me why that was irrelevant, or even why it happens, you lashed out at me. Furthermore, you say things like "400v FEEDING" which implies the problem exists in the supply of electricity, not the destination. Then, you say "led or OPEN CIRCUIT" which makes me ask the question, is there SOMEWHERE ELSE I should be looking for open circuit besides a bad led?

Thanks though for making me look like an ass because I don't have a bachelor's degree in television repair..

[budm]

Re: Samsung UE32EH5000 backlight issue fix

So far he is not convinced that he has problem with LEDs or open circuit, so I do not want to waste my time on that thread any more.

[Dannyx]

Re: Samsung UE32EH5000 backlight issue fix

His power supply board is not the same as your board.
https://www.badcaps.net/forum/showthread.php?t=67594

Yeah, I didn't notice the models were slightly different, but reading his post, I too would concur there's a dead LED somewhere - get to crackin' that sucker open, I'm afraid

[budm]

Re: Samsung UE32EH5000 backlight issue fix

His power supply board is not the same as your board.
https://www.badcaps.net/forum/showthread.php?t=67594

[Dannyx]

Re: Samsung UE32EH5000 backlight issue fix

400V ?! That's way over the maximum rating of the stock cap (and even the replacement one, since the one I installed is 250v). Also, the backlight should turn on without the main board connected, so just leave it disconnected at all times instead of bothering with it. Have you replaced the caps yet ?

Can't remember exactly what I got on those wires, but it definitely wasn't as high.