Problems with Samsung 740N monitors

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  • Chungalin
    Badcaps Veteran
    • Jul 2014
    • 422
    • Spain

    #461
    Re: Problems with Samsung 740N monitors

    I got one of these for repair. No backlight. Image OK.

    As expected, 3 bloated CapXon 820uF/25V (C111, C112, C301) and open 3A fuse (F301). Replaced everything and that's all.

    Comment

    • Behemot
      Badcaps Legend
      • Dec 2009
      • 4845
      • CZ

      #462
      Re: Problems with Samsung 740N monitors

      Test transformers and tubes as well.
      Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

      Exclusive caps, meters and more!
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      Comment

      • Venomus28
        Member
        • Oct 2016
        • 38
        • Albania

        #463
        Re: Problems with Samsung 740N monitors

        Hello forum
        I am a new member and i thought to post on this thread since i hope to help other people as it helped me.
        I have two SyncMaster 940T monitors with the stand by light on and no image.
        I found 3 bulged capacitors, which i am going to buy and replace tomorrow.
        Thinking to get the 3A pico fuse too
        I will keep you posted if that resolves my problem and if not id be very thankful if veteran members on this forum could help me getting further.

        Comment

        • bidomo
          New Member
          • Oct 2016
          • 3
          • mexico

          #464
          Re: Problems with Samsung 740N monitors

          Hey everyone!

          This thread seems a little cold, so let's hope someone still reads this so I can get some help...

          Well, in my case (740N), the fuse was blown, the capacitors are 1000uf 25v, I don't know if someone else replaced them and missed the fuse, the caps look fine (don't know how to identify the brand but will look into it).

          I replaced the fuse with a 4A 250v glass tube, , the monitor seems to work fine (I can test it after I get some sleep and go buy a VGA cable afterwards), the "check the signal cable" is there, it will take some time till I get the right fuses, but there seems like some people think it is ok to use this kind of fuse, when others don't.

          Is there a way to check if the inverter drivers are OK? I don't know much about electronics, but I'm willing to learn a little.

          Comment

          • Th3_uN1Qu3
            Believe in
            • Jul 2010
            • 6031
            • Romania

            #465
            Re: Problems with Samsung 740N monitors

            If you get the "check signal cable" screen then the inverter is OK. Sure you can check the MOSFET drivers, just use the diode check on your multimeter and measure between gate and drain, gate and source, drain and source. Measurements on the gate should check OPEN (OL or 1 on the left side), measurement between drain and source should show open one way and a diode drop the other.

            That is with the part out of circuit, in-circuit gate to source will more than likely show a diode drop because there will be another transistor driving it. Simplified version is this: Open or diode drop is OK, short (zero) or low voltage drops (under 100mV) mean there is a fault in the transistor.
            Originally posted by PeteS in CA
            Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
            A working TV? How boring!

            Comment

            • Venomus28
              Member
              • Oct 2016
              • 38
              • Albania

              #466
              Re: Problems with Samsung 740N monitors

              Hello forum i am back
              Ive replaced the 3 bulged caps with new ones with exact same value as the old ones
              Now the pico fuse i couldent get a same as old one green one but ive got a 3A smd fuse
              Can i use the smd one or i should keep looking for a "green" one ?

              Comment

              • Behemot
                Badcaps Legend
                • Dec 2009
                • 4845
                • CZ

                #467
                Re: Problems with Samsung 740N monitors

                You can use any pico fuse you can find. Usually with these THT ones there is enough room to even use glass pico fuse.
                Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                Exclusive caps, meters and more!
                Hardware Insights - power supply reviews and more!

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                • Venomus28
                  Member
                  • Oct 2016
                  • 38
                  • Albania

                  #468
                  Re: Problems with Samsung 740N monitors

                  Up the new one
                  Bottom the old one
                  Attached Files

                  Comment

                  • Behemot
                    Badcaps Legend
                    • Dec 2009
                    • 4845
                    • CZ

                    #469
                    Re: Problems with Samsung 740N monitors

                    If you can manage to solder it there…
                    Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                    Exclusive caps, meters and more!
                    Hardware Insights - power supply reviews and more!

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                    • bidomo
                      New Member
                      • Oct 2016
                      • 3
                      • mexico

                      #470
                      Re: Problems with Samsung 740N monitors

                      Originally posted by Behemot
                      If you can manage to solder it there…
                      The back side of the board seems safe to place it being SMD

                      Comment

                      • Venomus28
                        Member
                        • Oct 2016
                        • 38
                        • Albania

                        #471
                        Re: Problems with Samsung 740N monitors

                        Yes, i did that, the screen turned on for one second then, dark again lol
                        I bridged the fuse with a wire and now the stand by light pulses on and off ?
                        Ideas ?

                        Comment

                        • Th3_uN1Qu3
                          Believe in
                          • Jul 2010
                          • 6031
                          • Romania

                          #472
                          Re: Problems with Samsung 740N monitors

                          You have shorted mosfets in the inverter. See my post above on how to check them.
                          Originally posted by PeteS in CA
                          Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                          A working TV? How boring!

                          Comment

                          • Venomus28
                            Member
                            • Oct 2016
                            • 38
                            • Albania

                            #473
                            Re: Problems with Samsung 740N monitors

                            Send me the link please

                            Comment

                            • Venomus28
                              Member
                              • Oct 2016
                              • 38
                              • Albania

                              #474
                              Re: Problems with Samsung 740N monitors

                              So on one monitor i had three bulged capacitors and a blown fuse, can anyone tell me what should i check to know why the fuse blow ?
                              And on the other one as Th3 uNiQu3 member suggested i have three bulged capacitors, a blown fuse and both mosfets shorted
                              (The fuse are now both replaced with 3A SDM)
                              Last edited by Venomus28; 10-12-2016, 09:05 PM.

                              Comment

                              • dinesh111
                                New Member
                                • Jul 2014
                                • 1
                                • bangladesh

                                #475
                                Re: Problems with Samsung 740N monitors

                                thanks................................................

                                Comment

                                • jondoe
                                  Badcaps Veteran
                                  • Nov 2016
                                  • 547
                                  • UK

                                  #476
                                  Re: Problems with Samsung 740N monitors

                                  Thank you for everyone's input into this thread, I have an ip-35135b from an IBM Think Vantage monitor, which must be a rebadged Samsung.

                                  I've changed the three large filter caps for some 1000uf Suntans and replaced the pico fuse, only for the fuse to blow about an hour or so later. On closer inspection of the two AF4502C, one of them is testing for continuity from pin 3 to pins 5, 6, 7 and 8. That doesn't seem right and isn't reflected by the other. Probing around that circuit I found the ZD201 appears to be faulty, I get 0.2 on a diode test, on a working board it was 0.7, so I suspect it's fried.

                                  Does anyone know the package type/size of the ZD201? I'm not very familiar with surface mounts, but I'm happy to try and replace the mosfets and zener to see if comes back to life for more than a couple of hours

                                  Thanks.

                                  Comment

                                  • Behemot
                                    Badcaps Legend
                                    • Dec 2009
                                    • 4845
                                    • CZ

                                    #477
                                    Re: Problems with Samsung 740N monitors

                                    Usually you can replace SMD diode with leaded one.
                                    Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                                    Exclusive caps, meters and more!
                                    Hardware Insights - power supply reviews and more!

                                    Comment

                                    • jondoe
                                      Badcaps Veteran
                                      • Nov 2016
                                      • 547
                                      • UK

                                      #478
                                      Re: Problems with Samsung 740N monitors

                                      Sounds reasonable, but I wondered as the one installed has three pins, and leaded only has the two legs, how would I solder that in?

                                      Comment

                                      • Behemot
                                        Badcaps Legend
                                        • Dec 2009
                                        • 4845
                                        • CZ

                                        #479
                                        Re: Problems with Samsung 740N monitors

                                        Have you identified it? Some of them SOT-23 just have single diode with one end connected to two of the pins. Some actually have two diodes in single package (series, parallel or anti-parallel).
                                        Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                                        Exclusive caps, meters and more!
                                        Hardware Insights - power supply reviews and more!

                                        Comment

                                        • jondoe
                                          Badcaps Veteran
                                          • Nov 2016
                                          • 547
                                          • UK

                                          #480
                                          Re: Problems with Samsung 740N monitors

                                          I haven't quite identified it. I gather it's a 7.5 Zener of some description, I'm rather a novice at this kind of thing. Attached is an image as best I can make of it.
                                          Attached Files

                                          Comment

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