ViewSonic N2751W dead power board

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  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #41
    Re: ViewSonic N2751W dead power board

    I can clearly see that one end of R303 is connected to pin 3 VCC, pin 7 is also VCC and connected to the startup running cap?.
    I can see d304 Cathode connected to pin 7 VCC? And the anode is connected to???? gnd pin 1??. If it is then you need to check the resistance of that D304 also.
    Last edited by budm; 09-23-2016, 12:14 AM.
    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

    • WHaThEFLuX
      Badcaps Veteran
      • Feb 2015
      • 277
      • USA

      #42
      Re: ViewSonic N2751W dead power board

      It's M Ohms, and I have to correct my last post.......

      I mistakenly lifted pin 7 which also happens to be VCC, I just re checked it with pin 3 lifted(the one that connects to the 3 series resistors and the filter cap).

      When putting the leads to pin 1(GND) and pin 3 lifted (the correct VCC), I get open, so I'm guessing that means the IC is definitely bad.
      "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

      -retiredcaps

      Comment

      • WHaThEFLuX
        Badcaps Veteran
        • Feb 2015
        • 277
        • USA

        #43
        Re: ViewSonic N2751W dead power board

        You are correct, it is connected to the + leg of the 10 uf 50V cap.
        "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

        -retiredcaps

        Comment

        • WHaThEFLuX
          Badcaps Veteran
          • Feb 2015
          • 277
          • USA

          #44
          Re: ViewSonic N2751W dead power board

          so it looks like I need to order the LD7552BS?

          https://www.utsource.net/ic-datashee...S-1702334.html
          "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

          -retiredcaps

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #45
            Re: ViewSonic N2751W dead power board

            I updated post 41, so please read it again.
            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

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA

              #46
              Re: ViewSonic N2751W dead power board

              Originally posted by WHaThEFLuX
              It's M Ohms, and I have to correct my last post.......

              I mistakenly lifted pin 7 which also happens to be VCC, I just re checked it with pin 3 lifted(the one that connects to the 3 series resistors and the filter cap).

              When putting the leads to pin 1(GND) and pin 3 lifted (the correct VCC), I get open, so I'm guessing that means the IC is definitely bad.
              Yes, I think you found the problem.
              D304 ZENER is good then (REF TO POST 41).
              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

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #47
                Re: ViewSonic N2751W dead power board

                Originally posted by WHaThEFLuX
                so it looks like I need to order the LD7552BS?

                https://www.utsource.net/ic-datashee...S-1702334.html
                Yes, I would order more than one since that IC is used alot in other power supply too. I order lots of part from UTSOURCE before without any problems so far.
                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

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #48
                  Re: ViewSonic N2751W dead power board

                  BTW, it is much easier to see how the IC is connected on the board because you can see traces running under the IC when the IC is not installed.
                  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

                  • WHaThEFLuX
                    Badcaps Veteran
                    • Feb 2015
                    • 277
                    • USA

                    #49
                    Re: ViewSonic N2751W dead power board




                    Hope that helps, D304 shows 0.00 to OL in one direction, and 1.200 M Ohms falling to ~0.850 M Ohms in the other direction.
                    "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

                    -retiredcaps

                    Comment

                    • WHaThEFLuX
                      Badcaps Veteran
                      • Feb 2015
                      • 277
                      • USA

                      #50
                      Re: ViewSonic N2751W dead power board

                      Last question for the evening, I've used UTSOURCE many times before and sometimes it can take a while for the pieces to arrive(for someone with no patience). I tried to match the LD7552BS to some ICs from mouser, is that too much of a long shot?

                      http://www.mouser.com/Semiconductors...roller&FS=True


                      It must be time for bed, I was way off with that link, this one is closer but there's no SOP-8 packages.......

                      http://www.mouser.com/Semiconductors...roller&FS=True
                      Last edited by WHaThEFLuX; 09-23-2016, 12:43 AM.
                      "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

                      -retiredcaps

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #51
                        Re: ViewSonic N2751W dead power board

                        Those are for PWM Motor drive circuits.
                        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

                        • WHaThEFLuX
                          Badcaps Veteran
                          • Feb 2015
                          • 277
                          • USA

                          #52
                          Re: ViewSonic N2751W dead power board

                          I believe what little brain capacity I have is now depleted, thank you so much for your help, I will order that IC from UTSOURCE and update you when it's on the board!
                          "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

                          -retiredcaps

                          Comment

                          • WHaThEFLuX
                            Badcaps Veteran
                            • Feb 2015
                            • 277
                            • USA

                            #53
                            Re: ViewSonic N2751W dead power board

                            Bud, thanks to your incredible diagnostic skills, I've replaced the STDBY SMPS IC and am now getting 5V at the standby points! Do I have the green light to start buttoning the monitor back up or is there anything else you want me to verify?
                            "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

                            -retiredcaps

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #54
                              Re: ViewSonic N2751W dead power board

                              Thanks for the follow-up on the repair, I would hook everything back up and see if the TV will work, if it does then I would recap the secondary side next.
                              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

                              • WHaThEFLuX
                                Badcaps Veteran
                                • Feb 2015
                                • 277
                                • USA

                                #55
                                Re: ViewSonic N2751W dead power board

                                No problem, what exactly do you mean by secondary side?
                                "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

                                -retiredcaps

                                Comment

                                • budm
                                  Badcaps Legend
                                  • Feb 2010
                                  • 40746
                                  • USA

                                  #56
                                  Re: ViewSonic N2751W dead power board

                                  There are 7 lytics caps in the secondary (cold) side of the board.
                                  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

                                  • WHaThEFLuX
                                    Badcaps Veteran
                                    • Feb 2015
                                    • 277
                                    • USA

                                    #57
                                    Re: ViewSonic N2751W dead power board

                                    ahhh I see, I'll definitely do that, I'lll test the monitor when I get home from work and let you know how it went!
                                    "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

                                    -retiredcaps

                                    Comment

                                    • WHaThEFLuX
                                      Badcaps Veteran
                                      • Feb 2015
                                      • 277
                                      • USA

                                      #58
                                      Re: ViewSonic N2751W dead power board

                                      The plot thickens....


                                      I connected everything and turned the unit on, and it's working! About 20 seconds later, I see a nice trail of smoke coming from power supply board followed by the classic smell of burning PCB.

                                      I immediately unplugged it, removed it from the monitor and found the culprit. I can take a picture later if you'd like but there's really no need, I found a shorted diode near the 12V/24V power supply but I can't seem to identify it.

                                      It looks like a normal rectifier diode, with the markings S1 AR 62 on it....I wonder if it's a variation of the 1N4001?
                                      "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

                                      -retiredcaps

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #59
                                        Re: ViewSonic N2751W dead power board

                                        What is the designator as printed on the board, D????
                                        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

                                        • WHaThEFLuX
                                          Badcaps Veteran
                                          • Feb 2015
                                          • 277
                                          • USA

                                          #60
                                          Re: ViewSonic N2751W dead power board

                                          D402
                                          "You can only learn so much doing simple recapping and fixes. Ideally you want a really hard one to fix where you end up with a lot of dead ends and frustration. Then, and only then, do you learn how things really work."

                                          -retiredcaps

                                          Comment

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