Constant fuse blowing

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  • Techboxcomputer
    Senior Member
    • Aug 2016
    • 61
    • USA

    #1

    Constant fuse blowing

    Hi All


    Hi I have a Samsung UN40HU6950 TV that blew it's fuse on the power board. The board is a SE9B505102. I bought a matched ceramic fuse for it, reinstalled the board and it immediately blew the new one. I am at a loss of what to do next

    Thanks in advance = )
  • diif
    Badcaps Legend
    • Feb 2014
    • 6978
    • England

    #2
    Re: Constant fuse blowing

    The fuse is blowing for a reason, usually shorted a shorted component(s) on the power supply.
    You will need a multimeter to help find the faulty part(s) and to help us good photos of the board. I think it's a BN44-00752A ?

    Comment

    • Techboxcomputer
      Senior Member
      • Aug 2016
      • 61
      • USA

      #3
      Re: Constant fuse blowing

      I have a multimeter and I am not totally unfamiliar with it's use. The board is exactly the one you have mentioned. Tell me what you want photos off and I will post them

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: Constant fuse blowing

        Good clear high res straight shot of the whole top and bottom side of this power supply 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

        • Techboxcomputer
          Senior Member
          • Aug 2016
          • 61
          • USA

          #5
          Re: Constant fuse blowing

          OK - here they are. Let me know if you need anything better.
          Attached Files

          Comment

          • CapLeaker
            Leaking Member
            • Dec 2014
            • 7972
            • Canada

            #6
            Re: Constant fuse blowing

            check out the bridge rectifier BD8015 to see if it is shorted and the PFC fets next to it.

            Comment

            • steves7839
              Badcaps Veteran
              • Nov 2014
              • 200
              • USA

              #7
              Re: Constant fuse blowing

              One way to detect a shorted board is to measure resistance on the "load" or protected side of the fuse to circuit ground. Usually it will read just a few ohms if a downstream short exists.
              To isolate whether the short is located on the power board or another board, disconnect cables from the power board and remeasure.

              Comment

              • Techboxcomputer
                Senior Member
                • Aug 2016
                • 61
                • USA

                #8
                Re: Constant fuse blowing

                OK, lets address this one a a time, here are what my readings on my bridge rectifier is.
                With positive lead on leg one ( + ) and negative on leg 2 - .502
                With positive lead on leg one ( + ) and negative on leg 3 - .502
                With positive lead on leg one ( + ) and negative on leg 2 - tests through


                As far as the PFc's go, I am assuming you are telling me DP803 & DP804 These I am unsure how to test I now have noticed a slight discoloration around DP801c on the back of the board This sits between QP802cs & QP801cs and they read differently
                Last edited by Techboxcomputer; 11-06-2017, 09:47 AM.

                Comment

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #9
                  Re: Constant fuse blowing

                  Check the resistance between the two legs of the main filter cap, and also between the two outer legs of the bridge rectifier.
                  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

                  • Techboxcomputer
                    Senior Member
                    • Aug 2016
                    • 61
                    • USA

                    #10
                    Re: Constant fuse blowing

                    The 2 outer legs ring continuity on BD801s

                    If you are referring to the 2 500v68uf capacitors as the main filter cap(s) they both ring continuity also

                    The mosfet I am suspicious of is posted below. I may be wayyyy off as I am new to this but it looks like there was a heat issue with the middle one.
                    Attached Files

                    Comment

                    • budm
                      Badcaps Legend
                      • Feb 2010
                      • 40746
                      • USA

                      #11
                      Re: Constant fuse blowing

                      We need the reading in Ohms, continuity test does not mean much when looking for resistance value, continuity is telling you that you have connection between the two points, the resistance will tell me if it is normal or not.
                      Make sure to report if the reading is in Ohm, K Ohm, or M Ohm.
                      Yes, those are the two power MOSFET's for the PFC circuit and one PFC diode on that heatsink.
                      Last edited by budm; 11-07-2017, 10:15 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

                      • Techboxcomputer
                        Senior Member
                        • Aug 2016
                        • 61
                        • USA

                        #12
                        Re: Constant fuse blowing

                        Ok, as I said, I am still learning, so be patient please
                        Here is what I went by
                        " Connect the 'Source' of the MosFet to the meter's negative (-) lead.

                        1) Hold the MosFet by the case or the tab but don't touch the metal parts of the test probes with any of the other MosFet's terminals until needed.

                        2) First, touch the meter positive lead onto the MosFet's 'Gate'.

                        3) Now move the positive probe to the 'Drain'. You should get a 'low' reading. The MosFet's internal capacitance on the gate has now been charged up by the meter and the device is 'turned-on'.

                        4) With the meter positive still connected to the drain, touch a finger between source and gate (and drain if you like, it does not matter at this stage). The gate will be discharged through your finger and the meter reading should go high, indicating a non-conductive device."


                        Now that you read that (if that is correct) here are my results testing the 3 mosfets I pictured. On the backside of the board I put my negative on the left and my positive on the right. My meter is set in "diode mode" Here is where I am confused. When set on that on my expensive multimeter it just beeped continuity, when I pulled out my cheap radio shack multimeter I got a reading. If I am on the right path, please continue to point me towards what to test. If not redirect me please
                        Mosfet 1 - 0.0
                        Mosfet 2 - 0.0
                        Mosfet 3 -.356

                        *note - pulled out my more expensive meter again, and it beeped on the first two as before, but on the third mosfet it measured 1.16 odd that the other meter measured .356?

                        Thank you
                        Last edited by Techboxcomputer; 11-07-2017, 02:44 PM. Reason: another test

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA

                          #13
                          Re: Constant fuse blowing

                          No power applied to the board, then just put meter in Ohm mode and read the resistance between Source pin and the Drain pin and then tell use how many Ohms you get on the meter, make sure to report exactly what you see on the meter to whether it is in Ohm, K Ohm, or M Ohm.
                          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

                          • Techboxcomputer
                            Senior Member
                            • Aug 2016
                            • 61
                            • USA

                            #14
                            Re: Constant fuse blowing

                            Okay from the mosfets pictured in my last attachment left to right (This is taken on the back of the board with one lead on the right pin and one lead on the middle pin)

                            1 .5 OHMS
                            2 1.1 OHMS
                            3 .7 OHMS

                            Hope this helps

                            Thanks
                            Last edited by Techboxcomputer; 11-08-2017, 02:08 PM.

                            Comment

                            • Dumah Brazorf
                              Senior Member
                              • Jun 2013
                              • 179
                              • Italy

                              #15
                              Re: Constant fuse blowing

                              Originally posted by Techboxcomputer
                              OK, lets address this one a a time, here are what my readings on my bridge rectifier is.
                              With positive lead on leg one ( + ) and negative on leg 2 - .502
                              With positive lead on leg one ( + ) and negative on leg 3 - .502
                              With positive lead on leg one ( + ) and negative on leg 2 - tests through
                              Sorry i'm not english and i don't understand what do you mean by "tests through".
                              You did not test all possible connection, at least 6 measures, and ensure there's .5V or more.

                              Comment

                              • Moreno83
                                Badcaps Legend
                                • Jun 2014
                                • 2008
                                • The Netherlands

                                #16
                                Re: Constant fuse blowing

                                I think he means continuity with " tests through ".
                                I only repair Panasonic plasma tv's! Currently owning a TX-P55VT50 and still searching for a ZT60!

                                Comment

                                • budm
                                  Badcaps Legend
                                  • Feb 2010
                                  • 40746
                                  • USA

                                  #17
                                  Re: Constant fuse blowing

                                  Originally posted by Techboxcomputer
                                  Okay from the mosfets pictured in my last attachment left to right (This is taken on the back of the board with one lead on the right pin and one lead on the middle pin)

                                  1 .5 OHMS
                                  2 1.1 OHMS
                                  3 .7 OHMS

                                  Hope this helps

                                  Thanks
                                  Remove one MOSFET one at a time and then test it off the board again, so far you you do have shorted MOSFET.
                                  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

                                  • CapLeaker
                                    Leaking Member
                                    • Dec 2014
                                    • 7972
                                    • Canada

                                    #18
                                    Re: Constant fuse blowing

                                    something is shorted all right... but like budm already suggested: take one FET out at a time and check it, then put it back in its place. Not that you get mixed up later on where did what go.

                                    Comment

                                    • Techboxcomputer
                                      Senior Member
                                      • Aug 2016
                                      • 61
                                      • USA

                                      #19
                                      Re: Constant fuse blowing

                                      So, rather then checking in circuit, you want me to desolder and resolder each mosfet? What am I looking for on the read for each mosfet?

                                      Thanks

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #20
                                        Re: Constant fuse blowing

                                        Originally posted by Techboxcomputer
                                        So, rather then checking in circuit, you want me to desolder and resolder each mosfet? What am I looking for on the read for each mosfet?

                                        Thanks
                                        Yes, remove it and test it of the board the same way as you tested before, the one we looking for the most is the resistance reading between Source and Drain pin.
                                        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

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