Problems with Samsung 740N monitors

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  • Harvey
    Badcaps Veteran
    • Apr 2007
    • 264

    #21
    Re: Problems with Samsung 740N monitors

    Anyone know if the 720N uses the same, or similar, PSU?

    Comment

    • Soulace1970
      New Member
      • Feb 2009
      • 1

      #22
      Re: Problems with Samsung 740N monitors

      hi where is the 3A pico fuse found?

      Alex

      Comment

      • EGuevarae
        Badcaps Legend
        • Nov 2008
        • 1336
        • USA

        #23
        Re: Problems with Samsung 740N monitors

        This was ever resolved?
        I have a 940T with the same PSU. Power led brights in a beautiful blue color, but no image or backlight. Also, I can't get V readings on the three bloated caps on the pic. I have replaced ALL the caps in the board (except the little one on the inverter side. As soon as I get image, I'll mess with that.
        There are 10 kind of people in this world: those that understand binary, and those who don't.
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        • Bobdee
          Badcaps Veteran
          • Jun 2008
          • 461

          #24
          Re: Problems with Samsung 740N monitors

          Originally posted by Soulace1970
          hi where is the 3A pico fuse found?

          Alex
          Hello alex,
          I have not got a board with me, but from what I can see , there is a red fuse behind A/C connector,cylindrical in shape,but the one you may be after is possibly alongside of the big filter cap that is laying on ita side, its black and look like a diode or inductor,as I said I cant see properly from pictures,just check it out.
          bob

          Comment

          • EGuevarae
            Badcaps Legend
            • Nov 2008
            • 1336
            • USA

            #25
            Re: Problems with Samsung 740N monitors

            Originally posted by Soulace1970
            hi where is the 3A pico fuse found?

            Alex
            It is located under all that white stuff, at the side of a resistor, just at the side of the offending 820uf 25v caps.
            Attached Files
            Last edited by EGuevarae; 02-28-2009, 12:14 PM. Reason: Added a pic
            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

            • EGuevarae
              Badcaps Legend
              • Nov 2008
              • 1336
              • USA

              #26
              Re: Problems with Samsung 740N monitors

              Originally posted by eguevarae
              This was ever resolved?
              I have a 940T with the same PSU. Power led brights in a beautiful blue color, but no image or backlight. Also, I can't get V readings on the three bloated caps on the pic. I have replaced ALL the caps in the board (except the little one on the inverter side. As soon as I get image, I'll mess with that.
              Problem solved. While changin the fuse, checked the resistor at its side.
              Resistor under the white stuff was badly/cold soldered.
              Removed solder, resoldered, and now power flows in all the board.

              And for the V readings, one of the jumpers was also badly soldered. I reflowed the solder on it, and problem solved. Too bad that after the LCD came to life it has a green line (like 2~3 pixels wide) across the right side.It has been narrowed down to the LCD Panel itself, as I have another unit and the problem moves if I exchange the lcd panels...too bad, excellent image and no damage to the screen ...
              Attached Files
              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
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                2 x Acer KA240H + 1 Vewsonic VP2130 21 (a cap replacement job )

              Comment

              • gveranda
                Member
                • Mar 2009
                • 12

                #27
                Re: Problems with Samsung 740N monitors

                Originally posted by eguevarae
                This was ever resolved?
                I have a 940T with the same PSU. Power led brights in a beautiful blue color, but no image or backlight. Also, I can't get V readings on the three bloated caps on the pic. I have replaced ALL the caps in the board (except the little one on the inverter side. As soon as I get image, I'll mess with that.
                I Have a lcd with the same power board but it doesn't power at all I checked the voltages every where that i can see no readings at all even this big 1000uf 450v cap doesn't get any volt.can anyone here please help me to figure out anything thank you.really sorry if i pooped up the question in wrong location.

                Comment

                • Bobdee
                  Badcaps Veteran
                  • Jun 2008
                  • 461

                  #28
                  Re: Problems with Samsung 740N monitors

                  If you dont get green LED light up, check that red cyndrical fuse behind A/C connector, also fuse in power point plug.and the bridge rectifier

                  bob
                  Last edited by Bobdee; 03-05-2009, 09:00 AM.

                  Comment

                  • gveranda
                    Member
                    • Mar 2009
                    • 12

                    #29
                    Re: Problems with Samsung 740N monitors

                    Originally posted by Bobdee
                    If you dont get green LED light up, check that red cyndrical fuse behind A/C connector, also fuse in power point plug.and the bridge rectifier

                    bob
                    Thanks for the reply bob,red fuse was blown as youve said and i replace that but it keeps happening again.any other ideas?sorry my knowledge it very limited thanks

                    Comment

                    • PlainBill
                      Badcaps Legend
                      • Feb 2009
                      • 7034
                      • USA

                      #30
                      Re: Problems with Samsung 740N monitors

                      Originally posted by gveranda
                      Thanks for the reply bob,red fuse was blown as youve said and i replace that but it keeps happening again.any other ideas?sorry my knowledge it very limited thanks
                      If the fuse keeps blowing something is drawing too much current. Possible suspects are (in order) the switching transistor (on the large heatsink near the top of the large cap), the bridge rectifier (black rectangle near the bottom of the large cap), and the large cap itself. Use and ohmmeter and check each one out.

                      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

                      • gveranda
                        Member
                        • Mar 2009
                        • 12

                        #31
                        Re: Problems with Samsung 740N monitors

                        Originally posted by PlainBill
                        If the fuse keeps blowing something is drawing too much current. Possible suspects are (in order) the switching transistor (on the large heatsink near the top of the large cap), the bridge rectifier (black rectangle near the bottom of the large cap), and the large cap itself. Use and ohmmeter and check each one out.

                        PlainBill
                        Thanks PlainBIll Just checked the board carefully and found that green colour part in between cylindrical fuse and blue capacitor has burnt(just below the yellow cubic) I really appreciate if someone can name them for me and get the value of that green thing looks like a resistor to me.Thank you guys.

                        Comment

                        • EGuevarae
                          Badcaps Legend
                          • Nov 2008
                          • 1336
                          • USA

                          #32
                          Re: Problems with Samsung 740N monitors

                          Originally posted by gveranda
                          Thanks PlainBIll Just checked the board carefully and found that green colour part in between cylindrical fuse and blue capacitor has burnt(just below the yellow cubic) I really appreciate if someone can name them for me and get the value of that green thing looks like a resistor to me.Thank you guys.
                          Post a pic of your board , of the area with the suspected bad component.
                          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

                          • Bobdee
                            Badcaps Veteran
                            • Jun 2008
                            • 461

                            #33
                            Re: Problems with Samsung 740N monitors

                            tell us the letters/numbers on the board, probaby a thermistor, and any markings on it,
                            post pictures of your board if you can
                            Last edited by Bobdee; 03-07-2009, 04:32 AM.

                            Comment

                            • EGuevarae
                              Badcaps Legend
                              • Nov 2008
                              • 1336
                              • USA

                              #34
                              Re: Problems with Samsung 740N monitors

                              Originally posted by Bobdee
                              tell us the letters/numbers on the board, probaby a thermistor, and any markings on it,
                              Yep. If you can't post a pic, the marking on the silkscreen can help. I should have suggested that before.
                              Thanks, Bob.
                              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
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                              • GeForce GT1050
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                              Comment

                              • Bobdee
                                Badcaps Veteran
                                • Jun 2008
                                • 461

                                #35
                                Re: Problems with Samsung 740N monitors

                                sorry Eduardo,I did not know you posted on it,I was typing my reply while you posted ,I take ages to type anything

                                Comment

                                • EGuevarae
                                  Badcaps Legend
                                  • Nov 2008
                                  • 1336
                                  • USA

                                  #36
                                  Re: Problems with Samsung 740N monitors

                                  Originally posted by Bobdee
                                  sorry Eduardo,I did not know you posted on it,I was typing my reply while you posted ,I take ages to type anything
                                  That is what makes this forum great : we complement each other. And it is nice to know that I'm not alone typing at 3:00AM too
                                  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

                                  • Bobdee
                                    Badcaps Veteran
                                    • Jun 2008
                                    • 461

                                    #37
                                    Re: Problems with Samsung 740N monitors

                                    It was easier for me, 11.00 AM here, but Im a Night Owl as well

                                    Comment

                                    • EGuevarae
                                      Badcaps Legend
                                      • Nov 2008
                                      • 1336
                                      • USA

                                      #38
                                      Re: Problems with Samsung 740N monitors

                                      Originally posted by Bobdee
                                      It was easier for me, 11.00 AM here, but Im a Night Owl as well
                                      I forgot you are at the other side of the Atlantic. Now It is official : I am the only member browsing at 3:00am
                                      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

                                      • Bobdee
                                        Badcaps Veteran
                                        • Jun 2008
                                        • 461

                                        #39
                                        Re: Problems with Samsung 740N monitors

                                        yep , agreed

                                        Comment

                                        • mladen82
                                          Member
                                          • Mar 2009
                                          • 39
                                          • Montenegro

                                          #40
                                          Re: Problems with Samsung 740N monitors

                                          I have repair many these boards from 740N too. Always three 820uF/25V CapXon GL 105 caps and one fuse 3A (axial green) after them. They are all on +13V power line which supplies inverter board.
                                          In primary side there is an Fairchild smps pwm controller FSDM0565R.
                                          Always too, on solder side of pcb, we can see that power copper lines +13V have some more yellow color than rest of board (that is green) and conlusion is that there was some over current flow.

                                          Caps are bad quality for sure but there may be also some overvoltage on secondary side caused by iregular state of whole smps, even overvoltage from power line 220-240V.

                                          Discovering right causes can be painful and ready for academic discuss.

                                          Best way is to test new board with over voltage, high ambient temperature, open and short output circuits etc.

                                          Caps and fuse aren't cheap and can't be problem, but when main A/D board or even lcd panel is dead also (on some other models) it can be a problem to judge whole case, as i have some.
                                          https://www.badcaps.net/forum/showth...6020#post66020

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