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Samsung 940b - classic nod backlight problem

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    #21
    Re: Samsung 940b - classic nod backlight problem

    Thank you. I will desolder tehm now and measure again.

    Ebay won't ship to serbia in any case, and if someone agrees to do it outside of ebay it's pretty expensive. I'll have to find another way

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      #22
      Re: Samsung 940b - classic nod backlight problem

      Originally posted by bocca View Post
      Ebay won't ship to serbia in any case, and if someone agrees to do it outside of ebay it's pretty expensive. I'll have to find another way
      Take a copy of the 4502C datasheet to your local electronics store and maybe you can find an equivalent part?
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        #23
        Re: Samsung 940b - classic nod backlight problem

        http://www.digikey.rs/rs/en/digihome.html

        $120 fixed rate shipping to Serbia? lol
        Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

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          #24
          Re: Samsung 940b - classic nod backlight problem

          ugh, there's not an easy way to desolder these is there? :-\

          @jasgriff: yeah, that's what i'm talking about. And if you order something chances are it's gonna "get lost" in the customs. Most of the things I ordered never arrived...

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            #25
            Re: Samsung 940b - classic nod backlight problem

            Are you trying to remove the 8 pin chip?
            Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

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              #26
              Re: Samsung 940b - classic nod backlight problem

              That's right. One problem is, the soldering wick can't be found here anywhere. (Most never heard of the stuff). Is there any way to do it without it?

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                #27
                Re: Samsung 940b - classic nod backlight problem

                Even if you did have solder wick you would probably find that it wouldn't get all of the solder off and risk you lifting a pad as you attempt to pull it off.
                Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

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                  #28
                  Re: Samsung 940b - classic nod backlight problem

                  I use stainless steel razor blade or eXACTO blade inserting under the melted soldeer IC pin of the IC to separate the pin from the pad if you have no other tools to do it with, just take your time doing it. Main key is that you should have 40watts soldering Iron so the tip can maintain the temperature without heating up the traces and damage the trace, most people using 25~3watts iron which does not have enough heat capacity to maintain the temprature.
                  Last edited by budm; 03-16-2012, 03:21 PM.
                  Never stop learning
                  Basic LCD TV and Monitor troubleshooting guides.
                  http://www.badcaps.net/forum/showthr...956#post305956

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                  http://www.badcaps.net/forum/showthr...999#post300999

                  Inverter testing using old CFL:
                  http://www.badcaps.net/forum/showthr...er+testing+cfl

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                    #29
                    Re: Samsung 940b - classic nod backlight problem

                    I do have powerful enough iron, and that razorblade trick is pretty neat. I'll try it asap

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                      #30
                      Re: Samsung 940b - classic nod backlight problem

                      Two of the 8 legs came off along with all the solder on the board. I guess that can't be that easily fixed...

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                        #31
                        Re: Samsung 940b - classic nod backlight problem

                        Can you show us a picture of what's happened?
                        Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

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                          #32
                          Re: Samsung 940b - classic nod backlight problem

                          sure can

                          here's a photo. i believe you'll destinguish my messup
                          Attached Files

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                            #33
                            Re: Samsung 940b - classic nod backlight problem

                            Originally posted by bocca View Post
                            sure can

                            here's a photo. i believe you'll destinguish my messup
                            Its not that bad of a mess! these things happen.

                            I'm pretty sure you can get away with patching the Pins with the missing pads to the next nearest connection.

                            The board looks clean what did you use?
                            Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

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                              #34
                              Re: Samsung 940b - classic nod backlight problem

                              good, so there is still some hope

                              You will have to guide me on that nearest connection business, as I'm not sure I quite got it.


                              Clean in what sense? General cleanliness or soldering stuff? Thnx, by the way

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                                #35
                                Re: Samsung 940b - classic nod backlight problem

                                Originally posted by bocca View Post
                                You will have to guide me on that nearest connection business, as I'm not sure I quite got it.
                                Basically you have to figure out where those pads connect to in the circuit. If you look at the datasheet the two solder pads you lifted are either pins 6 and 7 or pins 2 and 3. I can't tell from the photo and regulars will notice that in one thread yesterday, I can't tell north from south in a diagram.

                                If there is any solder pad left, then you may be able to use the continuity beep on your multimeter to find out where the pads connect to. Then you can use some wire to bridge the connection.

                                Something like this ...

                                http://www.circuitrework.com/guides/6-1.shtml
                                Last edited by retiredcaps; 03-20-2012, 05:54 AM.
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                                  #36
                                  Re: Samsung 940b - classic nod backlight problem

                                  Originally posted by retiredcaps View Post
                                  Basically you have to figure out where those pads connect to in the circuit. If you look at the datasheet the two solder pads you lifted are either pins 6 and 7 or pins 2 and 3. I can't tell from the photo and regulars will notice that in one thread yesterday, I can't tell north from south in a diagram.

                                  If there is any solder pad left, then you may be able to use the continuity beep on your multimeter to find out where the pads connect to. Then you can use some wire to bridge the connection.

                                  Something like this ...

                                  http://www.circuitrework.com/guides/6-1.shtml
                                  That site offers some fantastic examples of patching. Much better than my response P.s Never Eat Shredded Wheat N-E-S-W.
                                  Fixed so far : 1 Home cinema system, 16 LCD Monitors, 4 LCD TV's

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                                    #37
                                    Re: Samsung 940b - classic nod backlight problem

                                    Wow, thanks retiredcaps

                                    I will do what you both proposed, and try to look for a place to bridge the connection

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                                      #38
                                      Re: Samsung 940b - classic nod backlight problem

                                      you can desolder this little mosfets (8pin smd) with a little pliers.
                                      take the ic whit the pliers and add solder to four legs on both sides,then pull up
                                      you must add heat on both sides quickly 2 or 3 times.

                                      just repaired one samsung syncmaster 153v , whit 2 of 4 AO4600 mosfet shorted,due to dry capacitors.

                                      My soldering iron is a "JBC" 25W, whit soldering tip slightly curved.

                                      sorry for my english,hahaha, i use google translator sometimes..

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                                        #39
                                        Re: Samsung 940b - classic nod backlight problem

                                        Originally posted by retiredcaps View Post
                                        Both mosfets above are bad. Desolder both and retest S2-G2 out of circuit to verify that read around 1.0 ohms. If still shorted, then replacements are available on ebay. 8 for $4.80 + free shipping.
                                        Exactly my problem, thanks bro

                                        Nah, exactly the right transistors are in one shop here but I don't like the price, worth $4 a piece. Pretty expensive, it will barely make any money when display sold after repair…

                                        EDIT// found a thread here on slovakian forums, a guy replaced them with IRF7389. They are third the price and actually on local stock. Slightly worse current parameters, but who gives a shit, there will be less than 0,3 A of current running through both of them…(rating of the backlight is 650 V/7,5 mA which equals to less than 5 W).
                                        Last edited by Behemot; 03-25-2012, 08:21 AM.
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                                          #40
                                          Re: Samsung 940b - classic nod backlight problem

                                          Bocca please what is the resistance of R316 resistor? It is next to the 33uF C345 cap on the upper side. I have slightly burned it due to short between S1 and G2
                                          Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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