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Help with Tatung TLM-1905 LCD no power at all

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    #1

    Help with Tatung TLM-1905 LCD no power at all

    I have a Tatung LCD monitor that does nothing at all. No LED on power button nothing at all. It had some bad caps which I replaced and that did nothing. I hooked the back lights to a different brand power supply and the display itself works fine. With power plugged in I have voltage on the large yellow transformer on the plug side nearest the big filter cap. Around 60v. I would think that mean the bridge rectifier is fine as well as filter on the output side of the transformer I have nothing. No voltage at all. I checked the resistance on the output and it is roughly 1 ohm. Would that indicate the transformer is dead? It does not seem to have been hot. There is no writing on the transformer to determine a proper replacement. Am I on the right track? Are these transformers some what universal? Any idea what I could replace it with? I would be tempted to buy a board but I can't seem to locate one. It is a LM004 Rev 3.
    Attached Files
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    #2
    Re: Help with Tatung TLM-1905 LCD no power at all

    Have you checked the fuse at F1,?

    Check for continuity - post result in ohms
    Check voltage on each side Black probe on ground screw probe each side with red
    Meter on 200vDC
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment

      #3
      Re: Help with Tatung TLM-1905 LCD no power at all

      F1 checks fine

      Comment

        #4
        Re: Help with Tatung TLM-1905 LCD no power at all

        Where circled in black I got voltage. Red circles, nothing.
        Attached Files

        Comment

          #5
          Re: Help with Tatung TLM-1905 LCD no power at all

          Originally posted by selldoor View Post
          Have you checked the fuse at F1,?

          Check for continuity - post result in ohms
          Check voltage on each side Black probe on ground screw probe each side with red
          Meter on 200vDC
          I didnt say but you need to post result of voltage test.
          Please upload pictures using attachment function when ask for help on the repair
          http://www.badcaps.net/forum/showthread.php?t=39740

          Comment

            #6
            Re: Help with Tatung TLM-1905 LCD no power at all

            When troubleshooting consumer electronics, one of the most important voltages to look for is standby DC voltage. This is typcially 5V DC.

            In consumer electronics, we rarely need to measure AC.

            List pin number and DC voltage for the connector like so (black probe goes on a ground screw on chassis).

            pin 1 = 0.0
            pin 2 = 5.0
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            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.

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              #7
              Re: Help with Tatung TLM-1905 LCD no power at all

              See budm's lcd troubleshooting guide in my sig file link in the above post for the basics.
              --- 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: Help with Tatung TLM-1905 LCD no power at all

                Originally posted by selldoor View Post
                I didnt say but you need to post result of voltage test.
                on 200v DC tested ground to each side of F1. Nothing. 0. Also tested ground to each pin connector. All 0. Ground screw to input side of transformer 63 v. I will try to get better pictures and read the guide.

                Comment

                  #9
                  Re: Help with Tatung TLM-1905 LCD no power at all

                  Between the BIG cap and the transformer there is a small cap - what voltage is on that meter on vdc200 probe on each leg joint
                  Please upload pictures using attachment function when ask for help on the repair
                  http://www.badcaps.net/forum/showthread.php?t=39740

                  Comment

                    #10
                    Re: Help with Tatung TLM-1905 LCD no power at all

                    Originally posted by selldoor View Post
                    Between the BIG cap and the transformer there is a small cap - what voltage is on that meter on vdc200 probe on each leg joint
                    it is c109 and it has 64.5 on each leg to ground.

                    Also testing with meter on 200 vdc the area in orange is the only area of the board with any power at all.
                    Attached Files
                    Last edited by jbshocks; 02-03-2013, 02:29 PM.

                    Comment

                      #11
                      Re: Help with Tatung TLM-1905 LCD no power at all

                      But this ground is NOT the same as the other one you used.You must measure across the small cap itself,Black to the side where the stripe, is red to the other side.

                      Comment

                        #12
                        Re: Help with Tatung TLM-1905 LCD no power at all

                        Originally posted by Rtech View Post
                        But this ground is NOT the same as the other one you used.You must measure across the small cap itself,Black to the side where the stripe, is red to the other side.
                        Measuring across c109 (small cap) 0 v dc

                        Comment

                          #13
                          Re: Help with Tatung TLM-1905 LCD no power at all

                          Across the Big cap you should have approx 155v DC IF your mains voltage is 110V AC ????

                          Comment

                            #14
                            Re: Help with Tatung TLM-1905 LCD no power at all

                            across the big cap is 169 v DC. Here is a little better picture. I don't have a very good camera.
                            Attached Files

                            Comment

                              #15
                              Re: Help with Tatung TLM-1905 LCD no power at all

                              Provided that is the Start up cap !! then you need to identify the part code written on U101,on the bottom of the board, as this looks to be the SMPS chip,you then need to find the datasheet for that,see what pin that cap goes to etc.Also there should be a diode connected to the positive side of that cap,the other side of the diode going to the transformer ??

                              Comment

                                #16
                                Re: Help with Tatung TLM-1905 LCD no power at all

                                chip says sg3842gs. I can see on the board it goes to pin 7, verified with an ohm meter.

                                Comment

                                  #17
                                  Re: Help with Tatung TLM-1905 LCD no power at all

                                  FYI, found this thread. https://www.badcaps.net/forum/showthread.php?t=14042 Same power supply same symptoms. I tested pin 5 to 7 nothing. in fact tested pin 5 to all pins. Only pin 3 was non zero and fluctuated between .8 and .9v. Unfortunately no resolution was posted.

                                  Comment

                                    #18
                                    Re: Help with Tatung TLM-1905 LCD no power at all

                                    At first look at the datasheet, then 15V DC needed between 5 and 7,which is the same as across the cap,and you have nothing.You need to check the diode connected to the +ve side of the cap, undo one end and check either with resistance or diode test on the meter...POWER OFF for this.You can replace the cap and try that as well, otherwise as these transformers do not usually fail...I have never seen one fail..you would need to replace the chip I suspect.

                                    Comment

                                      #19
                                      Re: Help with Tatung TLM-1905 LCD no power at all

                                      diode reads 500 one direction and nothing in the other in diode test mode. This is out of circuit. I could easily change out the chip. My concern is that I have no voltage on the chip vcc
                                      Last edited by jbshocks; 02-04-2013, 11:46 AM.

                                      Comment

                                        #20
                                        Re: Help with Tatung TLM-1905 LCD no power at all

                                        The required start-up current is typically only 5uA. This
                                        ultra-low start-up current allows designers to supply the
                                        start-up power required by the SG384xG using a
                                        high-resistance and a low-wattage start-up resistor.Thats from the datasheet,so on initial switch on some current is drawn from the Rectifier Bridge to the VCC Pin to start
                                        off the sequence to get the chip running.If the chip is faulty then you could get exactly the symptoms you have.

                                        Comment

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