Announcement

Collapse
No announcement yet.

Samsung LTN1785w Inverter and CCFL Voltages

Collapse
X
Collapse
 
  • Page of 2
  • Filter
  • Time
  • Show
Clear All
new posts
Previous 1 2 template Next
    #1

    Samsung LTN1785w Inverter and CCFL Voltages

    Hi All,

    About a year ago, I picked up a Samsung LTN1785w 17" Widescreen TV / Monitor combination that was manufactured in June 2003 for $20 on Craigslist. This unit only has an NTSC Analog tuner built in, and all the standard analog inputs - Component, Composite, S-Video, VGA, and Antenna.

    The inverter consists of 4 circuits that drive 8 CCFLs - 2 CCFLs per circuit. The top 2 lamps do not light at all. The bottom 2 lamps light for approximately 10 minutes, then turn off. The middle 4 lamps work perfectly. I swapped around all the lamps into all the 4 circuits - there is no fault with the lamps. The top and bottom circuits are faulty. I can not find any obvious fault with the discreet components or transformers, but I could not test the 4 SMD IC chips - I suspect that the fault is with them.

    I have not been able to find a service manual, or schematic diagram of the inverter. I also have not been able to find a replacement inverter on eBay at any price, but I am not willing to invest too much money in this unit. The LCD is perfect, and has a very nice picture when watching a DVD - so it's technically not a cheap piece of junk.

    What I would like to do, just for the fun of it, is to drive the 4 lamps with external inverter units - they are fairly cheap on eBay. I know that CCFLs range in voltage from approximately 700v to 2000v - I do not know what the voltage rating of the lamps in this unit are - this is the information that I am looking for.

    I am not trying to repair the inverter, but I am attaching 3 pictures of it for your reference - they are 3 different attempts at getting a clear and readable view. There are absolutely no components on the back of the board.

    IC1, IC2, IC3, IC4 - are all marked SEM2001L S307
    C12, C32, C112, C132 - are all marked H334 3894

    Thank you for any help that you can provide.
    Attached Files
    Last edited by crtfool; 02-08-2011, 04:38 PM. Reason: spelling
    Tags: None
    #2
    Re: Samsung LTN1785w Inverter and CCFL Voltages

    Originally posted by crtfool View Post
    I can not find any obvious fault with the discreet components or transformers
    Did you test the inverter transformer? See

    http://lcdparts.net/TransformerDetai...ProductID=3191

    This part is close. See if your secondaries measure around 530 ohms?
    --- begin sig file ---

    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

    Please do not post inline and offsite as they slow down the loading of pages.

    --- end sig file ---

    Comment

      #3
      Re: Samsung LTN1785w Inverter and CCFL Voltages

      Thanks retiredcaps - all the secondaries are between 612 and 660 ohms.

      T1=613 T2=649 T3=660 T4=642 T5=660 T6=623 T7=615 T8=618
      Last edited by crtfool; 02-08-2011, 05:15 PM. Reason: added individual readings

      Comment

        #4
        Re: Samsung LTN1785w Inverter and CCFL Voltages

        PlainBill states that they should all be within 3% of each other.
        --- begin sig file ---

        If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

        We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

        Please do not post inline and offsite as they slow down the loading of pages.

        --- end sig file ---

        Comment

          #5
          Re: Samsung LTN1785w Inverter and CCFL Voltages

          T1 and T2 are for the bottom lamps that light for 10 minutes.
          T7 and T8 are for the top lamps that do not light at all.

          With the 3% theory, I can conclude that T1, T7, and T8 are most likely faulty - do you concur?

          Comment

            #6
            Re: Samsung LTN1785w Inverter and CCFL Voltages

            As a test, you could desolder T5, T6, T7, T8 and swap positions. That is T7 and T8 go where T5 and T6 are.

            Right now, you say the top lamps never light up. By swapping the transformers, this will narrow down the problem to the transformer or the circuitry.
            --- begin sig file ---

            If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

            We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

            Please do not post inline and offsite as they slow down the loading of pages.

            --- end sig file ---

            Comment

              #7
              Re: Samsung LTN1785w Inverter and CCFL Voltages

              Originally posted by crtfool View Post
              With the 3% theory, I can conclude that T1, T7, and T8 are most likely faulty - do you concur?
              Maybe try the changing of the transformer positions first.

              I would hate to suggest you spend the money for 3 transformers and have it not work.
              --- begin sig file ---

              If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

              We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

              Please do not post inline and offsite as they slow down the loading of pages.

              --- end sig file ---

              Comment

                #8
                Re: Samsung LTN1785w Inverter and CCFL Voltages

                I just noticed that LT-17R is in the odd number position and LT-17 are in the even number position.

                I don't know if it matters, but if you swap transformer positions, keep that in mind.
                --- begin sig file ---

                If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                Please do not post inline and offsite as they slow down the loading of pages.

                --- end sig file ---

                Comment

                  #9
                  Re: Samsung LTN1785w Inverter and CCFL Voltages

                  I,m thinking that T1, T3, T5, T7 all should be near 660 ohms because the middle circuits have the transformers that are 660 ohms - T1 and T7 are much lower at 613 and 615. These are the LT-17R transformers.

                  T7 and T8 are almost equal, yet that pair of lamps do not light.

                  I will try swapping a pair of working transformers into the circuit that is not lighting at all, and get back to you.

                  Thanks.

                  Comment

                    #10
                    Re: Samsung LTN1785w Inverter and CCFL Voltages

                    Originally posted by crtfool View Post
                    T7 and T8 are almost equal, yet that pair of lamps do not light.
                    Sorry, I should have clarified. If the "correct" ohms reading is 660 for the secondary transformer, T7-615 and T8-618 are signficantly off relative to 660.
                    --- begin sig file ---

                    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                    Please do not post inline and offsite as they slow down the loading of pages.

                    --- end sig file ---

                    Comment

                      #11
                      Re: Samsung LTN1785w Inverter and CCFL Voltages

                      Yes, I agree. I think that the LT-17R transformers should be closer to 660. I think that the T8 at 618 might be OK because T6 is 623. I am going to move a 660 LT-17R into the T7 position, pairing it with T8 at 618, and see if the lamps light at all - since they do not light right now.

                      Comment

                        #12
                        Re: Samsung LTN1785w Inverter and CCFL Voltages

                        OK - we have initial success - I put a 660 ohm LT-17R in the T7 position with the 618 ohm T8 and the top lamps now light up. I have to give it a longevity test to be sure that it will hold.

                        Thanks retiredcaps -you really know this well!

                        I really did not think that it was a transformer problem because they were not seriously out of spec, but I guess the pairs have to be balanced to work properly.

                        I am concerned about buying 530 ohm transformers to mix with the mating transformers that are in the 640 ohm range. There must be a reason that the pairs are 2 different transformers - "17" and "17R". The LT-17R are green while the LT-17 are yellow. Any further advice, or a link to an exact replacement would be appreciated.
                        Last edited by crtfool; 02-08-2011, 07:17 PM. Reason: added more info

                        Comment

                          #13
                          Re: Samsung LTN1785w Inverter and CCFL Voltages

                          Originally posted by crtfool View Post
                          Thanks retiredcaps -you really know this well!
                          I only have a surface level understanding. PlainBill explains it best at

                          https://www.badcaps.net/forum/showpo...8&postcount=14
                          --- begin sig file ---

                          If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                          We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                          Please do not post inline and offsite as they slow down the loading of pages.

                          --- end sig file ---

                          Comment

                            #14
                            Re: Samsung LTN1785w Inverter and CCFL Voltages

                            More explanations by PlainBill can be found by searching for

                            constant current AC source

                            here on this forum.
                            --- begin sig file ---

                            If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                            We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                            Please do not post inline and offsite as they slow down the loading of pages.

                            --- end sig file ---

                            Comment

                              #15
                              Re: Samsung LTN1785w Inverter and CCFL Voltages

                              So far the top lamps are staying lit - and now that the top lamps are working on T7 and T8, the bottom lamps on T1 and T2 are also staying lit (I did not swap these transformers) - they may be tied in with each other. I have the middle lamps disconnected because I removed the LT-17R transformers from their circuits.

                              Comment

                                #16
                                Re: Samsung LTN1785w Inverter and CCFL Voltages

                                Originally posted by crtfool View Post
                                I am concerned about buying 530 ohm transformers to mix with the mating transformers that are in the 640 ohm range. There must be a reason that the pairs are 2 different transformers - "17" and "17R". The LT-17R are green while the LT-17 are yellow. Any further advice, or a link to an exact replacement would be appreciated.
                                The one I linked to at lcdparts.net is not an exact match. That one is LT-17B. The last letter may be significant and might mean a revision or a new part altogether?

                                Also, I forgot to tell you to measure the LT-17R and LT-17 inverter out of circuit to see if anything in circuit is affecting the ohms reading.

                                You might want to phone lcdparts.net and ask them if they have a LT-17R. They get new stock all the time. Or search ebay for a LT-17R.
                                --- begin sig file ---

                                If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                                We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                                Please do not post inline and offsite as they slow down the loading of pages.

                                --- end sig file ---

                                Comment

                                  #17
                                  Re: Samsung LTN1785w Inverter and CCFL Voltages

                                  I did get a higher reading on the 2 LT-17R transformers out of circuit. The transformers are warm now, so I am getting different readings at the moment on all the transformers - higher. I have the unit off and cooling down - I will post the readings soon, but they may still be different because I have 2 transformers removed.

                                  I did check eBay, and did an internet search - nothing available. If I can't find a replacement, I may let it sit for a while because I was more interested in solving this problem - I did not expect to actually find out what was wrong with the inverter board this quickly.

                                  Comment

                                    #18
                                    Re: Samsung LTN1785w Inverter and CCFL Voltages

                                    I'm going to explain my thought process on the relative resistances, and the limitations of the measurements.

                                    Wikipedia probably has an article on the process of making wire. Essentially copper ore is refined, cast into bars, then pulled through a die that is very slightly smaller than the bar. The resulting wire is drawn through progressively smaller and smaller diameter dies (with heat treatments taking place to keep it malleable) until it reaches it's final diameter. It then gets coated with varnish as insulation. Impurities, variations in diameter, etc, will affect the resistance, but these should average out.

                                    Transformers are wound by placing a fixed number of turns onto a bobbin. This parameter is controlled carefully. A test technique is used that will detect an error of a single turn on a winding. And it is the turns ratio that is critical. Depending on the logistics of the winding facility, I would expect identical windings made from a single roll of wire to measure within 1%, possibly within .2%. Variations between winding machines, spools of wire from different lots, etc will increase the range.

                                    The big variation is when company XYZ decides to wind 'equivalent' transformers as a substitute for those made by company ZYX. The wire will certainly come from a different production lot, the winders will be different, tension setting may be different, and a different gauge of wire may be used. However, it is the number of turns on the primary and secondary that are important.

                                    In this case, it would be instructive to use a ring tester to check the transformers. I'd suspect that only two bad transformers would be found.

                                    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

                                      #19
                                      Re: Samsung LTN1785w Inverter and CCFL Voltages

                                      Current resistance readings on all the transformers:

                                      T1=620 T2=652
                                      T3=N/A T4=640
                                      T5=N/A T6=631
                                      T7=669 T8=626 T7 was formerly in the T3 position

                                      Original readings:

                                      T1=613 T2=649
                                      T3=660 T4=642
                                      T5=660 T6=623 Original T5=OPEN out of circuit - this was working, but I might have damaged it when removing it
                                      T7=615 T8=618 Original T7=617 out of circuit

                                      Thanks plainbill for the info - I do understand tolerances and batch differences, but your explanation is very informative. I did learn a lot about inverter transformers and their dynamics in these few hours while retiredcaps was coaching me.

                                      Comment

                                        #20
                                        Re: Samsung LTN1785w Inverter and CCFL Voltages

                                        Originally posted by crtfool View Post
                                        Current resistance readings on all the transformers:

                                        T1=620 T2=652
                                        T3=N/A T4=640
                                        T5=N/A T6=631
                                        T7=669 T8=626 T7 was formerly in the T3 position

                                        Original readings:

                                        T1=613 T2=649
                                        T3=660 T4=642
                                        T5=660 T6=623 Original T5=OPEN out of circuit - this was working, but I might have damaged it when removing it
                                        T7=615 T8=618 Original T7=617 out of circuit

                                        Thanks plainbill for the info - I do understand tolerances and batch differences, but your explanation is very informative. I did learn a lot about inverter transformers and their dynamics in these few hours while retiredcaps was coaching me.
                                        Yeah, retiredcaps does pretty good explanations.

                                        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

                                        Previous 1 2 template Next
                                        Working...
                                        X