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    Re: Problems with Samsung 740N monitors

    Well i read the all thread once again, and i measured the 13V and 5.1V outputs. So the 5.1V is OK, but on the "13V" pin I have +18V. So I guess that I have the same problem like sequille and ethernet. I have some hissing sound too for 1-2 seconds, when the lamp is ON, after that the sound is off and the lamp goes off.
    Does anybody found what causes that symptoms ?

    Comment


      Re: Problems with Samsung 740N monitors

      hello,
      after reading all Threads 3 times, and working for 2 days on the psu, I am back to square 1.

      what i did

      replaced the 3 820 caps with new ones
      replaced the other elecrolitic caps with new ones
      re-solder ALL the joints
      Replaced the optocoupler with similar one,
      Tested All the Zener diodes, and most of the rezistors
      the invertor tranformers measurements are :
      1.406ohms and 1.348ohms

      Could the problem be located among the following components ? the MOSFETS, the FSDM0565R and the bit3193 pwm controller.I did not test them (as I do not know how).
      Like othes before i have 5.v reading and 18 v reading instead of 13.v
      the green transformer starts to make noise when I push the power button,


      i tried to unsolder 1 mosfet to measure, but it got destroyed in the process (one leg came off...) so i can not play with it anymore until the replacement mosfet ships in.

      That is all I can think at the moment,

      Big thank to everybody

      Comment


        Re: Problems with Samsung 740N monitors

        Originally posted by seemore
        1305 Ohms on the right transformer, and 1235 Ohms on the other one.
        That is about a 5% difference. I'd suspect a bad transformer. Still, it's time to make the other tests I've outlined. They will go a long way towards identifying the nature of the problem.

        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


          Re: Problems with Samsung 740N monitors

          Originally posted by lipi
          hello,
          after reading all Threads 3 times, and working for 2 days on the psu, I am back to square 1.

          what i did

          replaced the 3 820 caps with new ones
          replaced the other elecrolitic caps with new ones
          re-solder ALL the joints
          Replaced the optocoupler with similar one,
          Tested All the Zener diodes, and most of the rezistors
          the invertor tranformers measurements are :
          1.406ohms and 1.348ohms

          Could the problem be located among the following components ? the MOSFETS, the FSDM0565R and the bit3193 pwm controller.I did not test them (as I do not know how).
          Like othes before i have 5.v reading and 18 v reading instead of 13.v
          the green transformer starts to make noise when I push the power button,


          i tried to unsolder 1 mosfet to measure, but it got destroyed in the process (one leg came off...) so i can not play with it anymore until the replacement mosfet ships in.

          That is all I can think at the moment,

          Big thank to everybody
          I have one question - What is the problem you were having with the monitor?

          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


            Re: Problems with Samsung 740N monitors

            Hello and thank you for the reply

            Sorry about not mentioning the problem

            Apart from the 13 v being 18v (like many others), i have picture but no light.
            I will order the mosfets, and then do the other tests, that you mentioned.

            thank you again

            Comment


              Re: Problems with Samsung 740N monitors

              Originally posted by lipi
              Hello and thank you for the reply

              Sorry about not mentioning the problem

              Apart from the 13 v being 18v (like many others), i have picture but no light.
              I will order the mosfets, and then do the other tests, that you mentioned.

              thank you again
              The major part of the load on the 13 volt supply is probably the inverter. Without any load, it will go rather high.

              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


                Re: Problems with Samsung 740N monitors

                Hello again!
                I figured out the invertor I bought, powered it externally, the lamps turn on (i had to replace one of them, the inverter was buzzing and one of the lamps turned on partially). But i have another problem (which actually seems to cause the overload and the power supply switching on/off): if I place the lamps inside the metal panel, they... "hiss" (like TV static), but if i take them out and lay them on the table side by side, they work normally. If I touch a the metal reflector with a metal tool (isolated, don`t worry) the lamps get brighter (all 4 of them) and if I make contact between the two reflectors, the lamps start hissing again. So I thought I'd use some electrical tape for insulation (although the metal panel actually has to touch the reflectors, as there was some aluminum sheet stuck to both the metal panel and the reflectors). That seemed to work, as there was no hiss, until I noticed that the inverter's capacitors and the coils were getting very hot (in like 5 minutes, while i was trying to clean the plastic diffusers and align them). However, they don't get that hot if the lamps are outside the metal panel, not even after 15 minutes.
                I want to add that after they hiss, there's a strange smell coming off the reflectors, not of burnt circuitry but more ...chemical.
                This behavior seems very strange to me. Any thoughts, ideas?
                Last edited by sequille; 04-21-2010, 03:34 AM.

                Comment


                  Re: Problems with Samsung 740N monitors

                  Originally posted by sequille
                  Hello again!
                  I figured out the invertor I bought, powered it externally, the lamps turn on (i had to replace one of them, the inverter was buzzing and one of the lamps turned on partially). But i have another problem (which actually seems to cause the overload and the power supply switching on/off): if I place the lamps inside the metal panel, they... "hiss" (like TV static), but if i take them out and lay them on the table side by side, they work normally. If I touch a the metal reflector with a metal tool (isolated, don`t worry) the lamps get brighter (all 4 of them) and if I make contact between the two reflectors, the lamps start hissing again. So I thought I'd use some electrical tape for insulation (although the metal panel actually has to touch the reflectors, as there was some aluminum sheet stuck to both the metal panel and the reflectors). That seemed to work, as there was no hiss, until I noticed that the inverter's capacitors and the coils were getting very hot (in like 5 minutes, while i was trying to clean the plastic diffusers and align them). However, they don't get that hot if the lamps are outside the metal panel, not even after 15 minutes.
                  I want to add that after they hiss, there's a strange smell coming off the reflectors, not of burnt circuitry but more ...chemical.
                  This behavior seems very strange to me. Any thoughts, ideas?
                  Arcing. The is not the way I would have described the problem, but it is a very good description.

                  The 'chemical smell' is ozone. Look over the leads carefully; odds are there is a break in the insulation on a high tension lead, or a bad solder joint on the return lead.

                  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


                    Re: Problems with Samsung 740N monitors

                    Originally posted by PlainBill
                    Arcing. The is not the way I would have described the problem, but it is a very good description.

                    The 'chemical smell' is ozone. Look over the leads carefully; odds are there is a break in the insulation on a high tension lead, or a bad solder joint on the return lead.

                    PlainBill
                    I agree. The hiss is the most notorious signal, then the smell. Must be one of the lamps leaking. You should carefully inspect the solder joints in the lamps, under the plastic thing at the ends, specially on the thicker cable.
                    There are 10 kind of people in this world: those that understand binary, and those who don't.
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                      Re: Problems with Samsung 740N monitors

                      At least I did something for the planet
                      I'll do some checking then and I'll get back with the results.
                      Thanks for the answers.

                      Comment


                        Re: Problems with Samsung 740N monitors

                        Originally posted by sequille
                        At least I did something for the planet
                        I'll do some checking then and I'll get back with the results.
                        Thanks for the answers.
                        I give up. I re-soldered everything, used heat shrink tubing, laid all lamps on a metal sheet (while still out of the reflectors) and there's still arcing.
                        I'm just gonna buy a 1 meter SMD led strip and hope the 120 LEDs/1m (it's roughly 40 LEDs up and 40 down) is high enough of a density for not getting striped backlighting.
                        Thank you for your assistance.

                        Comment


                          Re: Problems with Samsung 740N monitors

                          do u mean that we can transform every monitor into a nice LED display ?
                          u will use something like this ?
                          http://www.dealextreme.com/details.dx/sku.5312
                          Please make a post when u finish ... i think it will be great And will solve many problems with that inverters and lamps ...

                          Comment


                            Re: Problems with Samsung 740N monitors

                            Originally posted by lipi
                            Hello and thank you for the reply

                            Sorry about not mentioning the problem

                            Apart from the 13 v being 18v (like many others), i have picture but no light.
                            I will order the mosfets, and then do the other tests, that you mentioned.

                            thank you again
                            I've ordered and replaced those 2 mofsets. Still the problem exists, so i give up. I'll try to find whole inverter board, or if i don't find, i may try that solution with the LED strip - sounds very interesting ... i have a strange feeling all that will end with one broken monitor in the recycle bin

                            Comment


                              Re: Problems with Samsung 740N monitors

                              hi there, im Ariel from argentina. i have a 740n with the usual problems, image its ok but no backlight. I manage to open the flat, and get PSU board. the 3 820u 25v are bumped and orange dust come from 1 of the 3.

                              so, i ll replace them. I test the pico fuse with tester and i think its ok, have to replace it anyway?

                              thx for ur help

                              Comment


                                Re: Problems with Samsung 740N monitors

                                Originally posted by maxavatar
                                hi there, im Ariel from argentina. i have a 740n with the usual problems, image its ok but no backlight. I manage to open the flat, and get PSU board. the 3 820u 25v are bumped and orange dust come from 1 of the 3.

                                so, i ll replace them. I test the pico fuse with tester and i think its ok, have to replace it anyway?

                                thx for ur help
                                If tested OK (not open), no you don't have to.
                                Boca or River Plate?
                                There are 10 kind of people in this world: those that understand binary, and those who don't.
                                • ASUS ROG Maximus IX Code
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                                Comment


                                  Re: Problems with Samsung 740N monitors

                                  boca.... but only for family story, im not soccer fan. I test the pico fuse with tester for conductivity and i get the buzz noise. So i think its ok, by the way i dont think i can get same fuse in local market.

                                  Comment


                                    Re: Problems with Samsung 740N monitors

                                    Originally posted by maxavatar
                                    boca.... but only for family story, im not soccer fan. I test the pico fuse with tester for conductivity and i get the buzz noise. So i think its ok, by the way i dont think i can get same fuse in local market.
                                    If it buzzes then it is OK.
                                    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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                                    • 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


                                      Re: Problems with Samsung 740N monitors

                                      I just got a 740N going (I Think. It has only been running for ~5min since the repair). I replaced the caps and the pico fuse. The only problem is that it seems to have a slight red tinge. CCFL Problem??
                                      I love putting bad caps and flat batteries in fire and watching them explode!!

                                      No wonder it doesn't work! You installed the jumper wires backwards

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                                      Comment


                                        Re: Problems with Samsung 740N monitors

                                        Originally posted by c_hegge
                                        I just got a 740N going (I Think. It has only been running for ~5min since the repair). I replaced the caps and the pico fuse. The only problem is that it seems to have a slight red tinge. CCFL Problem??
                                        Yes. Red/pink hue = at least one CCFL dying.
                                        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


                                          Re: Problems with Samsung 740N monitors

                                          Originally posted by eguevarae
                                          Yes. Red/pink hue = at least one CCFL dying.
                                          Not always. I have Samsungs where the backlit screen is pinkish, BUT the menus and "Test good" box etc all come up with a pristine white background. That points to the video processing being the source of the pink hue, not the backlights.

                                          Not saying that is the poster's case, but it can have other causes.
                                          Friends don't let friends buy Samsung ....

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