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Samsung 940N 2 Seconds fade to black

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    #1

    Samsung 940N 2 Seconds fade to black

    So my 2007 died last night after much trouble free service.
    I use it as a second screen, so it was easy to check that the graphics card was working fine, and that it was something with the screen. It stays on for maybe 2 seconds and then goes to black.
    Few months ago I actually tried to fix a friends 17" by changing all Caps, and that was way before I discoved this excellent forum. Unfortunately than did not work so I chucked it out.
    Now after reading this forum, I see it may not have been the caps, but maybe the transformer or something else.
    So here's the spec:
    PS is a Suntronix BN-44000123E, with 1 big cap, 4 mids and 1 small. I can get replacements for maybe $10.
    Transformer is a TMS91429CT, which I see is about $9 on EB. -
    Question - do I replace the Caps, the Transformer, or get my multimeter out?

    Thanks!
    Tags: None
    #2
    Re: Samsung 940N 2 Seconds fade to black

    Originally posted by jack-pwc View Post
    So my 2007 died last night after much trouble free service.
    I use it as a second screen, so it was easy to check that the graphics card was working fine, and that it was something with the screen. It stays on for maybe 2 seconds and then goes to black.
    Few months ago I actually tried to fix a friends 17" by changing all Caps, and that was way before I discoved this excellent forum. Unfortunately than did not work so I chucked it out.
    Now after reading this forum, I see it may not have been the caps, but maybe the transformer or something else.
    So here's the spec:
    PS is a Suntronix BN-44000123E, with 1 big cap, 4 mids and 1 small. I can get replacements for maybe $10.
    Transformer is a TMS91429CT, which I see is about $9 on EB. -
    Question - do I replace the Caps, the Transformer, or get my multimeter out?

    Thanks!
    Quick sequence for solving 'two seconds to black' problems.

    1. Replace any suspect caps (Elite, Suscon, Capxonand other caps on the bad caps list are automatically suspect).

    2. Compare the resistance of the transformer secondaries. If they don't match to within 3% replace the one with the lower resistance.

    3. Substitute known good CCFLs

    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

      #3
      Re: Samsung 940N 2 Seconds fade to black

      Hi,
      Thanks for the reply.

      1.
      All of the Caps are JH (maybe Jaing Haius) rated 105 degrees and look great.
      I will replace them with some Lelon 105 low ERS's I have.
      Ratings are:
      100uF 450V - Power supply
      68uF 25V - Power Supply
      330uF 16V - Supply to Video Card & CCFL Transformers
      1000uF 16V - Supply to Video Card & CCFL Transformers
      1000uF 25V - Supply to CCFL Transformers
      1000uF 25V - Supply to CCFL Transformers

      BTW it seems very difficult to get the 68uF. I maight have to leave that one for now.

      2.
      Can I measure the transformers without desoldering? I would think so.

      3.
      The CCFL's work on start up. Do you mean they could still work and also be faulty? Like they are out of spec? Unfortunately I do not have any spares.

      Comment

        #4
        Re: Samsung 940N 2 Seconds fade to black

        Some Pics attached
        Attached Files

        Comment

          #5
          Re: Samsung 940N 2 Seconds fade to black

          Originally posted by jack-pwc View Post
          2.
          Can I measure the transformers without desoldering? I would think so.

          3.
          The CCFL's work on start up. Do you mean they could still work and also be faulty? Like they are out of spec? Unfortunately I do not have any spares.
          2) Yes.

          3) See explanation post #10, #11 at (but you can get ideas from entire thread)

          https://www.badcaps.net/forum/showthread.php?t=12407
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            #6
            Re: Samsung 940N 2 Seconds fade to black

            Transformer measures as follows:

            T1
            Primary 0.1 Ohm
            Secondary 1.249 kOhm - and is rock solid

            T2
            Primary - starts at 100 kOhm and rises to 300 kOhm after 5 seconds
            Secondary - jumps around from 0.7 - 0.8 MOhm

            Comment

              #7
              Re: Samsung 940N 2 Seconds fade to black

              Originally posted by jack-pwc View Post
              T2
              Primary - starts at 100 kOhm and rises to 300 kOhm after 5 seconds
              Secondary - jumps around from 0.7 - 0.8 MOhm
              Desolder T2 and retest to make sure it is not affected by surrounding components.
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                #8
                Re: Samsung 940N 2 Seconds fade to black

                This ebay ad says the secondary should be around 1.1K ohm

                http://cgi.ebay.co.uk/TMS91429CT-Fau...item3cb30bf053

                If the transformer is indeed bad, I found 2x inverter transformers for a total of $5 USD with free shipping to Canada. It was just listed 6 hours ago.

                http://shop.ebay.com/i.html?_kw=TMS91429CT

                That is an excellent price for 2 transformers. Normally, 1 is around $12 to $20 each.
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                  #9
                  Re: Samsung 940N 2 Seconds fade to black

                  Hi,
                  You can see in the pics it is a combi transformer with both wound on one ferite.
                  Just desoldered and tested again, same results as before - 1 secondry is 1.25kOhm, the other is still all over the place.
                  I will buy one on EB and try that first.
                  Thanks for the help!

                  Comment

                    #10
                    Re: Samsung 940N 2 Seconds fade to black

                    Hey Jack,

                    Ive got the same problem for that monitor.. was wondering if you had any luck fixing the monitor. No bulging bad caps here either..

                    Comment

                      #11
                      Re: Samsung 940N 2 Seconds fade to black

                      Hi All,
                      Sorry very slack for not closing the thread.
                      I bought a transformer on eB, 2 for $5 I think, and soldered one to the PCB - all good normal service was resumed.
                      It's been running a few months now and has been perfect. Thanks to all on the forum for teh help, especially retiredcaps!

                      Comment

                        #12
                        Re: Samsung 940N 2 Seconds fade to black

                        Hi to all,
                        This board is the same as on Samsung 931BF model, and I have the same problem. my transfomer have on the primary side 0.1 Ohm and on secondary side 1.183KOhm and 1215Kohm. I this OK?

                        Comment

                          #13
                          Re: Samsung 940N 2 Seconds fade to black

                          Originally posted by golub View Post
                          Hi to all,
                          This board is the same as on Samsung 931BF model, and I have the same problem. my transfomer have on the primary side 0.1 Ohm and on secondary side 1.183KOhm and 1215Kohm. I this OK?
                          Assuming you did not make a typing error, you have identified the problem. Please confirm that one reads 1.183 Kohm while the other reads 1.215 Megohm. If you neglected to insert a decimal point (1.183K and 1.215K), they are probably good.

                          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

                            #14
                            Re: Samsung 940N 2 Seconds fade to black

                            Originally posted by golub View Post
                            secondary side 1.183KOhm and 1215Kohm. I this OK?
                            Yes, but just barely. 1183 x 1.03 = 1218 ohms. Or 1215 x 0.97 = 1178 ohms.

                            So now it is either bad caps, bad ccfl, or bad ccfl wiring (check the return - thinner wire).
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                            Comment

                              #15
                              Re: Samsung 940N 2 Seconds fade to black

                              Yes, I made mistake in typing, 1.215 KOhm, board is exactly the same as on pics in post #4, I will try to change the capatitors

                              Thanks

                              Comment

                                #16
                                Re: Samsung 940N 2 Seconds fade to black

                                I replace transformer and everything is OK.
                                Thank you all for help

                                Comment

                                  #17
                                  Re: Samsung 940N 2 Seconds fade to black

                                  Originally posted by golub View Post
                                  I replace transformer and everything is OK.
                                  Did you mean caps? In post #15, you said you were going to change the caps?
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                                    #18
                                    Re: Samsung 940N 2 Seconds fade to black

                                    I change my mind, I replace transformer, and it works

                                    Thanks

                                    Comment

                                      #19
                                      Re: Samsung 940N 2 Seconds fade to black

                                      Originally posted by golub View Post
                                      I change my mind, I replace transformer, and it works
                                      Good job. The transformer was just on the edge of the 3%.
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                                        #20
                                        Re: Samsung 940N 2 Seconds fade to black

                                        I have the same monitor. Has 2 seconds to black though can get it to stay on sometimes. Desoldered the inverter transformer and checked it

                                        S1 was 1.21 kOhm
                                        S2 was 1.1 kOhm

                                        Going to try a new inverter transformer since S2 seems way out.

                                        Comment

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