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    Samsung UE32EH5000 backlight issue fix

    Good day folks. Thought I'd report my findings on another one of these Samsung tellies and how I managed to fix it, so let me tell you a story first The reason I'm doing this is because it seems to be a fairly common occurrence, having encountered it myself and read about it a lot now, so I thought I'd add another one to that pile to perhaps same someone out there some time and effort. The first time I ran into this, I got stumped a lot before finally figuring it out, with a little help from our wonderful chaps here of course. I thought the issue might've been a one-off sort-of deal and didn't make a big deal out of it back then, but then I saw it happening again....and again...then read a post here of someone else who was struggling with it and managed to fix it "together" the same way. Here's the original post

    The backlight wasn't coming on....yeey. Now it may not sound like anything special and your first thought will be a bad backlight LED, mine was too of course, but they all checked out fine - exactly the same scenario as everybody else having this issue. To make a long story short, the problem is the power supply itself: it's a BN44-00493B in this case, but I imagine it can happen to other similar supplies as well, despite not having seen it myself, at least not yet.

    Even though you may be getting something out of the LED connector, like 160v, the LEDs still refuse to turn on, not even a flash or anything, and that's because of a faulty cap, CM867. Now here's the interesting bit which is bound to screw a lot of people over, me included: no visible signs of failure on this cap, so without an ESR meter you might look at it and think, nope, this one looks fine - leave it alone and move on...that was until, on a whim, I decided to pull it out and replace it anyway, since I had just about exhausted every other possibility at this point, including replacing the SLC1012C IC, checking and rechecking all resistors, even SMD ones and every last voltage on there. Turns out it WAS faulty: it had leaked through one of its legs, so that was the issue: I replaced it and I was all good do go.

    Now the same thing happened just as I'm writing this, so this being like the 4th time seeing this, I thought I just HAVE to write about it My buddy had already opened up the TV and checked the LEDs for me, but of course he got stumped the same way I did and had no idea what to check next, being at wits' end. After having a look myself, not trying to be cocky or anything, I went straight to that cap, pulled it out and lo and behold: failed leg once again, except unlike the last time where the leg was fine but the electrolyte spewed out and wasn't particularly obvious unless you got in really close with a magnifier, this leg had completely broken off, showing signs of corrosion. Replacing it instantly fixed the issue, so this goes to show that capacitors can fail even without showing it...which is nothing new, but larger ones like these usually tend to bulge, so you might disregard it initially thinking it's fine, when in reality it's leaked through the BOTTOM instead. In this case at least it's the exact same capacitor with the exact same issue, so it's particularly interesting and strange at the same time. Cheers guys
    Attached Files
    Wattevah...

    #2
    Re: Samsung UE32EH5000 backlight issue fix

    This is very interesting. Your commentaries are usually very, very long and very, very informative. I like take two days sometimes to read your posts. I will look at this e-cap and similar e-caps on LED Driver circuits in future. Could a faulty/weak e-cap cause repeat failure of backlights, even though the backlight setting was turned down, would be something I will investigate. Thanks again for the share and enjoyed it as always.

    Comment


      #3
      Re: Samsung UE32EH5000 backlight issue fix

      Originally posted by Andrew F. Ali View Post
      This is very interesting. Your commentaries are usually very, very long and very, very informative. I like take two days sometimes to read your posts. I will look at this e-cap and similar e-caps on LED Driver circuits in future. Could a faulty/weak e-cap cause repeat failure of backlights, even though the backlight setting was turned down, would be something I will investigate. Thanks again for the share and enjoyed it as always.
      Yes I tend to write novels....don't know if it's good or bad though. The way I see it is I'd rather be thorough than skimp on the details
      Wattevah...

      Comment


        #4
        Re: Samsung UE32EH5000 backlight issue fix

        It's good, my friend. You're Dannyx and that's your style. I enjoy your 'novels'. I'm sure it does take a lot of patience to write them, though.

        Comment


          #5
          Re: Samsung UE32EH5000 backlight issue fix

          I repaired a Samsung dlp a few years ago, the cap was only slightly bulged, but when I removed it it was rattling when I shook it. I cut it open just for the hell of it. The corrosion is on the positive leg. It's a Samwha 820uf/250v
          Attached Files

          Comment


            #6
            Re: Samsung UE32EH5000 backlight issue fix

            Mine was a Samwha too. Makes me wonder why they fail at the legs in this particular setup while normally they'd bulge...the way heat moves around a cap also influences its failure mode from what I know.
            Wattevah...

            Comment


              #7
              Re: Samsung UE32EH5000 backlight issue fix

              @Dannyx You're post gives me a glimpse of hope. I just acquired a 60" Samsung UN60FH6003 yesterday that has no backlights. I've checked in the dark and can see the picture on screen. When I first turn it on the standby light flashes 6 times. There is no flicker, flash, or visible attempt at the backlights coming on. I've been preparing my mind for the chore of replacing burned out leds, which feels almost worth it considering I got the tv for free. Does my issue sound relevant to yours enough that perhaps the fix is the same? I would much rather replace a cap on the board than pull the panel apart, hands down, any day!

              Comment


                #8
                Re: Samsung UE32EH5000 backlight issue fix

                I was wondering why your English is so good Dannyx...

                Comment


                  #9
                  Re: Samsung UE32EH5000 backlight issue fix

                  Originally posted by x_orange90_x View Post
                  @Dannyx You're post gives me a glimpse of hope. I just acquired a 60" Samsung UN60FH6003 yesterday that has no backlights. I've checked in the dark and can see the picture on screen. When I first turn it on the standby light flashes 6 times. There is no flicker, flash, or visible attempt at the backlights coming on. I've been preparing my mind for the chore of replacing burned out leds, which feels almost worth it considering I got the tv for free. Does my issue sound relevant to yours enough that perhaps the fix is the same? I would much rather replace a cap on the board than pull the panel apart, hands down, any day!
                  Well you could give it a shot anyway - very simple and nothing to lose
                  Wattevah...

                  Comment


                    #10
                    Re: Samsung UE32EH5000 backlight issue fix

                    Originally posted by Davi.p View Post
                    I was wondering why your English is so good Dannyx...
                    That and also my university degree is in translation
                    Wattevah...

                    Comment


                      #11
                      Re: Samsung UE32EH5000 backlight issue fix

                      Originally posted by Dannyx View Post
                      Well you could give it a shot anyway - very simple and nothing to lose
                      What kind of voltage did you get on your D+ wire? I unplugged my main board and still no backlights. I get 425v on the D+ wire which drops to 400v when I unplug the main board, and drops again to 292v when I reconnect the main board.

                      Comment


                        #12
                        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.
                        Wattevah...

                        Comment


                          #13
                          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
                          Never stop learning
                          Basic LCD TV and Monitor troubleshooting guides.
                          http://www.badcaps.net/forum/showthr...956#post305956

                          Voltage Regulator (LDO) testing:
                          http://www.badcaps.net/forum/showthr...999#post300999

                          Inverter testing using old CFL:
                          http://www.badcaps.net/forum/showthr...er+testing+cfl

                          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                          http://s807.photobucket.com/user/budm/library/

                          TV Factory reset codes listing:
                          http://www.badcaps.net/forum/showthread.php?t=24809

                          Comment


                            #14
                            Re: Samsung UE32EH5000 backlight issue fix

                            Originally posted by budm View Post
                            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
                            Wattevah...

                            Comment


                              #15
                              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.
                              Never stop learning
                              Basic LCD TV and Monitor troubleshooting guides.
                              http://www.badcaps.net/forum/showthr...956#post305956

                              Voltage Regulator (LDO) testing:
                              http://www.badcaps.net/forum/showthr...999#post300999

                              Inverter testing using old CFL:
                              http://www.badcaps.net/forum/showthr...er+testing+cfl

                              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                              http://s807.photobucket.com/user/budm/library/

                              TV Factory reset codes listing:
                              http://www.badcaps.net/forum/showthread.php?t=24809

                              Comment


                                #16
                                Re: Samsung UE32EH5000 backlight issue fix

                                Originally posted by budm View Post
                                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..

                                Comment


                                  #17
                                  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: "
                                  Originally posted by budm View Post
                                  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?

                                  Originally posted by Dannyx View Post
                                  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
                                  Last edited by budm; 02-13-2018, 02:46 PM.
                                  Never stop learning
                                  Basic LCD TV and Monitor troubleshooting guides.
                                  http://www.badcaps.net/forum/showthr...956#post305956

                                  Voltage Regulator (LDO) testing:
                                  http://www.badcaps.net/forum/showthr...999#post300999

                                  Inverter testing using old CFL:
                                  http://www.badcaps.net/forum/showthr...er+testing+cfl

                                  Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                  http://s807.photobucket.com/user/budm/library/

                                  TV Factory reset codes listing:
                                  http://www.badcaps.net/forum/showthread.php?t=24809

                                  Comment


                                    #18
                                    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
                                    Wattevah...

                                    Comment


                                      #19
                                      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.

                                      Comment


                                        #20
                                        Re: Samsung UE32EH5000 backlight issue fix

                                        Originally posted by x_orange90_x View Post
                                        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

                                        Comment

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