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Samsung UN46H203AF Bad Backlights and Bad Power Supply

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    Samsung UN46H203AF Bad Backlights and Bad Power Supply

    I have a bunch of Samsung TVs with bad backlights. They all have over 50-90% bad LEDs and need full replacements. Unlike LG models, the backlight does not shut down when a problem is detected and it appears the shorts may damage the power supply.

    I got strips from Aliexpress Rzconne brand strips for one UN46H203AF, did the replacement and 2 strips failed after 3 days even with backlight level reduced. The seller shipped me replacements and when I installed them, the backlights were flickering powered with the power supply (main cable disconnected, tested fine with LED tester). I got hold of another TV the same model with bad backlights as well and tried that power supply on the original TV and the backlights failed to come on at all. I ordered a used power supply on ebay and that power supply appears to work properly.

    On the flickering power supply and the no backlight power supply, the area around D9801 and Q9801 are noticeable darkened by heat. Part number is BN44-00771A. Checking D9801 in circuit, the no backlight PS measures 1V in reverse direction vs OL on the working PS. Diodes on all 3 show about 0.5V drop the forward direction.

    Will investigate a bit further but a schematic would help.
    Attached Files
    Last edited by neilc6; 03-27-2019, 02:55 PM.

    #2
    Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

    D9801 D9801C measured the same (1V reverse) when I removed it so I replaced it (original SF28G 600V/2A) temporarily with a MUR640 (600V/4A) and the backlights come on so now I have 2 working boards. Need to debug the flickering board.
    Last edited by neilc6; 03-27-2019, 03:44 PM.

    Comment


      #3
      Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

      The model number you listed is not correct. Is it UN46H5203AF? or UN46H6203AF?

      I would check IC9805 on bottom side of board near connector CNL802. This may be an LED voltage/current controller and may be failed.

      You can try swapping this IC from your working board to the flickering one to see if it makes any change.

      ------------------
      Also, you said D9801 and D9801C measured 1V both ways, which diode was actually the problem? They are different diodes (different parts) so did you only replace one of them? or did you replace both? and which one?

      Comment


        #4
        Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

        neilC, what did you think of those backlight strips? Will they last? I too have a bunch of 46" Samsungs that need full LED replacements.

        On those PS's, check for cold solder joints. I've had a few that flickered because of bad joints in the usual places. Reflowing those connections brought them back to life.

        Comment


          #5
          Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

          Model number is UN46H5203AF. Other bad led 46" is UN46EH5300F. Strips are lost in the mail and I am in the dispute process with Aliexpress but have to wait 60 days for resolution.

          Actual designator for the diode is D9801C.

          I have only found two sources online for the 46" strips for the Samsungs. Aliexpress and shopjimmy (double the price). Since the new Rzconne strips failed after three days, I'm not too sure. I have only run the replacement ones they sent me for a day.

          I have ordered 40" strips from seller meihua361000 on ebay which I have a good experience in the past. Searched his store and couldn't find 46" strips. I had some 40" ones before but sold them. Should have kept them. Model numbers UN40H5203AF and UN40EH5300F.

          Also have a Haier 40D3505 with bad leds waiting for replacements. This model suffers from eeprom failure as well.

          Running out of space in the house to lean lcd panels against the wall safely.

          Starting to appreciate the LG LNs which shutdown the backlight and only have between 1-4 bad leds that I can replace quickly.
          Last edited by neilc6; 03-29-2019, 09:15 AM.

          Comment


            #6
            Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

            Yah, I've searched the net too for those 46" strips and only found the same options as you. With 7-8 46"' that need strips, it has has be an economical option. If/when they come, I'll make sure to run them for a while first.

            I may have a PS for your 46 and you are at least in the same province.

            -JJ

            Comment


              #7
              Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

              I have the same power supply board, different model tv(UN46H6201). Based on what you've said I should check for bad LEDs too, before investing in trying to fix the power supply? In the past I've had great luck fixing computer monitors with CFL backlights that had leaking capacitors, but LED TV repair is brand new to me.

              Comment


                #8
                Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                On Samsung models, there is no protection shutdown of shorted LEDs so they will burn out until one goes open, the tv is too dim or there is power supply damage. The two original TVs I installed Rzconne LED strips came back a few months later even with the backlight turned down. Luckily, these strips have multiple suppliers on ebay and Aliexpress.
                Last edited by neilc6; 03-07-2021, 08:35 PM.

                Comment


                  #9
                  Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                  Are you saying Rzconne led strips are poor reliability? If it's only going to fix it for a few months I'd rather just toss the TV and buy new, they are so cheap now.

                  Comment


                    #10
                    Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                    Ok, so I tested the LED strips for continuity, 3 of 4 have infinite resistance; the remaining one shows 50k. Should I "expect" power supply damage from that? It doesn't produce any picture when you power it up, just a blinking red light.

                    Comment


                      #11
                      Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                      You cannot test LED strings by measuring resistance though you can test individually for shorts. You need to put in diode mode and test each one individually or use a LED tester. With this model, you will likely have 80 to 90% of them shorted. Lots of suppliers for these strips currently. At the time of the original post, they were very few.
                      Last edited by neilc6; 03-08-2021, 02:05 PM.

                      Comment


                        #12
                        Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                        Wouldn't testing the strip as a whole tell if a single LED was open? That's what I was trying to determine, and that's what I interpret the data to suggest. From what you say, however, failing closed ("shorted") is the more common mode?

                        In any case it sounds like I'll be needing new LED strips. Is it worth being brand/store conscious on that? aliexpress only reports one seller listing LEDs specifically for this model:

                        https://www.aliexpress.com/item/1005...archweb201603_

                        Comment


                          #13
                          Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                          I tried this test: plugging in the power board to teh LEDs but not to the mainboard. LEDs do not light. I tried measuring VDC on the pins supplying power to the LED strips. It was not easy to make good contact but best as I could tell there was only half a volt between the + and - pins. Meanwhile, the singed diode showed 280vdc, and the oversized blue 450v/100uf cap showed 380vdc. so it seems like it's not delivering power to the LEDs.

                          Comment


                            #14
                            Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                            Hello,

                            i have EU40H5300 with same power supply BN44-00771A. TV came with not back light. I removed LED strips, replaces 10 diodes, placed back. Tried if everything works (of course before i tested all 4 leds with cca 32V (11x3V) ) and BAANG in 3 seconds again maybe 12 LEDs were dead. Again replaced broken one, tested and BAAAANG. Now only 6 LED strip is broken. So i start measuring and from PSU comes nice 272 V!!! Acc. label it should be only 172V and by calc 4 strips by 11 LEDs is 44 by 3V should be round 132V. So my PSU is giving twice more voltage that why my LED blown. I check and replaced diod D9801C but now change.

                            PS: Nothing is burned, 5V and 13V for mainboard are present.

                            Any ideas ? Thanks.
                            Last edited by Marian.Bella; 09-21-2022, 12:22 PM.

                            Comment


                              #15
                              Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                              You need to replace all your LEDs with new strips and not do individual replacements. You still have an open circuit LED. LED driver circuits are current sources and the voltage is the drop against all the LEDs in series. An open circuit will cause the voltage reading to max out. LED failures are not random. They wear, burn out and have limited life like batteries and light bulbs.
                              Last edited by neilc6; 09-21-2022, 01:40 PM.

                              Comment


                                #16
                                Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                                Dear Neilc6,

                                Thanks for quick response. So 280v is ok ? I know it is current source and the volrage drops down. but form 280v to 130v ?
                                Why i should not to do individual replacement ? I did it many times without any issues. This first time, where i saw so many dead leds. Usually when they are in serie connected are broken 2-5. Here it was 10.

                                After two attemt. It is cheaper and much faster to replace them individual (checked with 2.6V which is dead), like ordering complete set of strips.
                                Attached Files
                                Last edited by Marian.Bella; 09-21-2022, 02:02 PM.

                                Comment


                                  #17
                                  Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                                  Unlike every other manufacturer, Samsungs don't have protection shutdown in their LED driver circuit. LEDs will burn out until the screen gets too dim, there is damage to the power supply, or one LED goes open circuit acting like a fuse. Strip prices are relatively inexpensive ordering from Aliexpress.
                                  Attached Files
                                  Last edited by neilc6; 09-21-2022, 02:52 PM.

                                  Comment


                                    #18
                                    Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                                    If you are worried about burning LED's, you can try incadescent bulb first.

                                    Comment


                                      #19
                                      Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                                      i was thinking to put some resistor between 3 or 5 kOhm in serie.

                                      Comment


                                        #20
                                        Re: Samsung UN46H203AF Bad Backlights and Bad Power Supply

                                        Originally posted by Marian.Bella View Post
                                        i was thinking to put some resistor between 3 or 5 kOhm in serie.
                                        That's very light load

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