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    #61
    Re: Problems with Samsung 740N monitors

    Originally posted by eguevarae
    My friend, glad you are back.
    Well, you now gave some more info. Now you say that the CCFLs are working with other board, which mostly eliminates them from the equation.
    As I've seen so far, there are many causes for either the blown/leaking caps or the fuse blowing.
    The only recent case of a Samsung PSU/Inverter that blew a fuse in front of me (after I had changed it) is a 203B Board. It had bad lamps, they drew a lot of current, and blew the fuse. I replaced the fuse and it blew again. The screen only flashed for a moment (as when the inverter fails) and then it was off again. After the blown fuse (as a note, I had recapped it already), I replaced it by one slow blow as the one in your pics, but instead of attaching the 203B lamps, I attached a set of lamps from a 18" I have. They lit evenly and without problem or fuses blowing all over the place. Then I reattached the 203B lamps, and as soon as I turned on the PSU (this model has a switch. Very convenient...), the screen flashed, the fuse blown, and I was pissed off.
    I took apart the lamps and they were loose or something (nearly broken), and the voltage arced to the reflection film on the inside of the rail that protect the lamps, and this short blew the fuse. In the end, the LCD itself was damaged, as I replaced he lamps only to find that the LCD has a vertical line in the middle. In this case, bad lamps blew the fuse.
    In a not-Samsung case (cases, I might say), the problem was the use of bad quality caps, at a 85c temp rating, in a poorly ventilated area and with a design that left heat sources too close to the caps : Proview/KDS/Sylvania/MAG & others using Mirage Electronics PSUs. I have cases (I document every damn thing I do) of PSUs with bad caps, bad lamps and blown fuses. I have observed too that when the lamps are old, they take more time to fully start up, drawing much current in the process. maybe you didn't see it because, as you say, your CCFLs are good, but attach a set of pink-hued lamps, and you'll see that you easily break the 3.15A barrier. I guess that the fuse is there for cases like this among other things. And each case is different. Maybe in a controlled environment the PSU behaves well, but if the user has the unit in a poorly ventilated area working around the clock every day, the chances that something goes wrong (especially with the superb quality of the Elites & capXons found in many PSUs), ranging for intermittent failures to sudden death caused by blown fuses, are high.
    agreed with all you said

    Comment


      #62
      Re: Problems with Samsung 740N monitors

      Hi Eveyone,

      Finally It is working here,If you guys weren't here i never would be able to fix it this is the first time i repaired a LCD.thanks everybody.

      I replaced the D2SB60 with KBL405 which i found one of my old CPU PSU and broke another one and found MF72-005D9 put that instead of SCK-053 as PlainBill said.

      KBL405 is 4A is that really a issue??and does anyone have any idea what may have caused to short the rectifier?

      PlainBill,Bobdee,eguevarae,mladen82 thanks for sharing your knowledge.

      cheers
      gveranda
      Attached Files

      Comment


        #63
        Re: Problems with Samsung 740N monitors

        Originally posted by gveranda
        Hi Eveyone,

        Finally It is working here,If you guys weren't here i never would be able to fix it this is the first time i repaired a LCD.thanks everybody.

        I replaced the D2SB60 with KBL405 which i found one of my old CPU PSU and broke another one and found MF72-005D9 put that instead of SCK-053 as PlainBill said.

        KBL405 is 4A is that really a issue??and does anyone have any idea what may have caused to short the rectifier?

        PlainBill,Bobdee,eguevarae,mladen82 thanks for sharing your knowledge.

        cheers
        gveranda
        I was about to post that I found the KBL405 in the 172N dead board that I have, when I saw that you have made it work using that very same part. I don't think that is an issue.
        As for the SCK-053 replacement, I guess it is OK what you did. It is used in the 172N too, along the KBL405, so it is OK.
        As for the reason it shorted, now that is a good question.....
        Now you have to find a fuse ....
        And congratulations
        There are 10 kind of people in this world: those that understand binary, and those who don't.
        • ASUS ROG Maximus IX Code
        • Intel Core i5-7600K 3.8GHz
        • 16gb GSKILL TridentZ RGB DDR4-3200
        • 1 M2 SSD + 2 WD Blue 1TB (Mirrored)
        • Windows 10 Pro x64
        • GeForce GT1050
          2 x Acer KA240H + 1 Vewsonic VP2130 21 (a cap replacement job )

        Comment


          #64
          Re: Problems with Samsung 740N monitors

          Originally posted by mladen82
          info about NTC thermistors used in psu's, they are not there for protection against surges
          they are there because of inrush current limiting
          more info
          http://www.ametherm.com/inrush-curre...revention.html

          thank PlainBill for force me to rethink about that

          Every day we can learn something new
          And sometime it seems like I am relearning the same 'new' this over and over. The onlg good part of being old is it beats the alternative.

          PlainBill
          For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

          Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

          Comment


            #65
            Re: Problems with Samsung 740N monitors

            Originally posted by PlainBill
            The only good part of being old is it beats the alternative.

            PlainBill
            There are 10 kind of people in this world: those that understand binary, and those who don't.
            • ASUS ROG Maximus IX Code
            • Intel Core i5-7600K 3.8GHz
            • 16gb GSKILL TridentZ RGB DDR4-3200
            • 1 M2 SSD + 2 WD Blue 1TB (Mirrored)
            • Windows 10 Pro x64
            • GeForce GT1050
              2 x Acer KA240H + 1 Vewsonic VP2130 21 (a cap replacement job )

            Comment


              #66
              Re: Problems with Samsung 740N monitors

              Originally posted by gveranda
              does anyone have any idea what may have caused to short the rectifier?
              I just repaired a KDS 717s (700P) which had 470uf 25v bulged Capxon caps, a blown fuse on the AC input (which got replaced and blown twice before getting to --->) and a shorted bridge rectifier (KPB206, substituted by KBP206g, same thing, taken from a dead Sceptre PSU Board). It has been running since the bridge was replaced (along the fuse again, of course) 18 hours ago, and the same questions echoes in my hangover tormented head : why it shorted ?!?!?!?!?!?
              There are 10 kind of people in this world: those that understand binary, and those who don't.
              • ASUS ROG Maximus IX Code
              • Intel Core i5-7600K 3.8GHz
              • 16gb GSKILL TridentZ RGB DDR4-3200
              • 1 M2 SSD + 2 WD Blue 1TB (Mirrored)
              • Windows 10 Pro x64
              • GeForce GT1050
                2 x Acer KA240H + 1 Vewsonic VP2130 21 (a cap replacement job )

              Comment


                #67
                Re: Problems with Samsung 740N monitors

                good work fellas, I must admit that one put my head in a bit of a spin,

                Comment


                  #68
                  Re: Problems with Samsung 740N monitors

                  Hai All, I have question if i can't find the 820uf caps, what caps is compatible?
                  and for the fuse i can't find what the compatible fuse?

                  thanx

                  Comment


                    #69
                    Re: Problems with Samsung 740N monitors

                    Originally posted by tj_style
                    Hai All, I have question if i can't find the 820uf caps, what caps is compatible?
                    and for the fuse i can't find what the compatible fuse?

                    thanx
                    Both the caps and fuses are available from Digi-Key, which happens to have a 'no minimum order, no handling charge' policy. They also will ship small orders by first class mail, so shipping will run less that $3.

                    While I haven't worked on these monitors, it would appear Digi-Key part number F2315-ND is the proper fuse, while P11221-ND is the proper capacitor.

                    PlainBill
                    For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                    Comment


                      #70
                      Re: Problems with Samsung 740N monitors

                      I have problem with backlight of Samsung 740N.
                      LCD panel is have the picture but backlight is dead
                      I try to replace the 820uF 25v bugled caps and 3A pico fuse.
                      but in my country am very hard to find 820uF 25v Caps and 3A pico fuse.
                      I try to replace 820uF 25v caps with 1000uF 25v, but too big and I try to change 820uF 25v with 470uF 35v then I change 3A pico fuse with 3A glass tube fuse.

                      moment I try, actually succeed.
                      which I wish to ask do 470uF 35v caps can replace 820uF 25v?

                      Comment


                        #71
                        Re: Problems with Samsung 740N monitors

                        @ tj_style
                        No. Really should get the 820uF caps. The increase in voltage is fine. The drop in capacitance isn't good.

                        They engineered it for 820uF, so there must be a good reason.

                        What is your country?

                        Cheers!
                        Toast
                        veritas odium parit

                        Comment


                          #72
                          Re: Problems with Samsung 740N monitors

                          i'm from indonesia.
                          how if i replace the 820uF 25v with 1000uF?

                          is possible?

                          Comment


                            #73
                            Re: Problems with Samsung 740N monitors

                            Yes. A bit more capacitance is generally okay.

                            In Post #4 of this thread, there are 2 power board pics. Is either one like yours? -

                            https://www.badcaps.net/forum/showpo...18&postcount=4

                            What brand and series were the bad caps?

                            What brand and series are you replacing them with? What brands do you have available to you there?

                            Personally, I would replace all of the electrolytic capacitors in that unit.

                            For Indonesia, I would contact our member and authorized seller Big Pope who is in China. He has Samxon caps and they would likely be a good choice. You can contact him and arrange what you need:

                            https://www.badcaps.net/forum/member.php?userid=682

                            See here also:
                            https://www.badcaps.net/forum/showthread.php?t=2928

                            Toast
                            veritas odium parit

                            Comment


                              #74
                              Re: Problems with Samsung 740N monitors

                              My Power board is like in post 12
                              https://www.badcaps.net/forum/showpo...4&postcount=12

                              the bad caps brand is CapXon, and i replace with caps from Rubycon.

                              1000uF is to big than 820uF, and i can't stick it to the power board.

                              Comment


                                #75
                                Re: Problems with Samsung 740N monitors

                                Hi all,
                                I have this prob too. I've put a 2200uf cap in sideways in place of the 3 x 820 figuring on the -20 +80 tolerances. But I can't find the fuse. Please, where is it?

                                Comment


                                  #76
                                  Re: Problems with Samsung 740N monitors

                                  It's all right. Found it in mladen82's photos.
                                  Thanks for your help.

                                  Comment


                                    #77
                                    Re: Problems with Samsung 740N monitors

                                    Oh dear. The new fuse blew within a second. The screen flashed at power on.
                                    Are there schematics for the power supply?
                                    Is it worth putting a slo-blo fuse in for F301?

                                    Comment


                                      #78
                                      Re: Problems with Samsung 740N monitors

                                      Originally posted by warragul
                                      Oh dear. The new fuse blew within a second. The screen flashed at power on.
                                      Are there schematics for the power supply?
                                      Is it worth putting a slo-blo fuse in for F301?
                                      No. The inverter circuit is drawing too much power. It is necessary to determine WHY the fuse blew. It could be a bad transistor, bad transformer, bad CCFL, bad cap, etc. Putting in a slo-blow fuse will allow it to work for a slightly longer period, but not so long as to allow meaningful troubleshooting.

                                      PlainBill
                                      For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                                      Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                                      Comment


                                        #79
                                        Re: Problems with Samsung 740N monitors

                                        check for componet that is hot, mainly smd 8pin mosfet

                                        Comment


                                          #80
                                          Re: Problems with Samsung 740N monitors

                                          Thanks again for the assist.
                                          I'm a little puzzled, though.
                                          This is the first SMPS I've encountered with a fuse in the output. These power supplies usually rely on the oscillator stopping if the load gets too much.
                                          The Topswitch chip manufacturer's suggested circuits I've found don't have output fuses either. Some sort of effect of the sort of load it's driving, perhaps?

                                          mladen82, am I right in assuming that the FETs are the small SMDs on the underside of the board? Can't find my magnifying glass. If so the fuse doesn't last long enough for it to get warm.

                                          Comment

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