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Sceptre X20G NAGA-II no power

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    Sceptre X20G NAGA-II no power

    Hello all, as described in my title I have a sceptre X20G Naga-II that has no power, no lights are coming on, on the panel buttons or screen. I have trouble shooted this monitor with no luck so far, what I have done so far is replaced a switching transistor (Q11) that was shorted, replaced all capacitors on ps board because I don’t have a esr meter I went ahead and just replaced all of them on the ps board, no caps were bulging before replacement, I also reflowed solder joints on the transformers. Checked the fuses f1 and f2 on the ps board with fluke 115 DMM both fuses were good. I’m stumped and don’t know where to go next with this project, also I can’t find a service manual for this monitor anywhere. I marked the voltage readings I’m getting from the pins that feed the main board hoping someone can tell me if anything looks off. Oh I also forgot to mention I marked Zener diode (ZD102) and Signal Diode (D103) on the bottom view of ps board with Permanent marker because I was getting a reading of .041 on the signal diode and .136 on the Zener Diode I Placed the negative or black lead on the cathode side of the diode when I got these readings, DMM set to diode check, but I dont know how to get the values to replace these components, any help would be appreciated. Thanks in advance!
    Attached Files
    Last edited by aftonr; 02-28-2012, 11:24 PM.
    “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

    #2
    Re: Sceptre X20G NAGA-II no power

    HI have you checked for voltage on the large Filter ?

    In case you dont know but sure you do test this in dc mode Red + black -
    and you should see about 165-170 volts

    Comment


      #3
      Re: Sceptre X20G NAGA-II no power

      Lecture 1. When troubleshooting it is important to take a methodical approach. Recognizing symptoms can help avoid wasting time and money.

      Lecture 2. You have given us an incredible amount of detail, and some very good pictures. One is missing and another leaves a lot to be desired, however.

      Preliminary results. Some of the voltages are unusual (9.1V), others are common (5.3V, 12.9V). What is missing seem to be the control signals to the inverter. The power supply / inverter seems to be working properly, there are problems on the signal card.

      Your tasks.

      On the picture of the power supply / inverter there are two heat sinks above the transformers (large yellow objects) and two more immediately to the right. The first two are for the power transistors, the second pair are for the output diodes. What are the part numbers of the components mounted on the heat sinks mid-right on the board?

      I've marked up the picture of the signal board. There are 5 LDO regulators circled in yellow, I've numbered the pins on one of them. For each of these, report the following information - part number, voltage on pins 1, 2, and 3 (use a mounting screw as the ground point).

      There are two switching regulators circled in blue. What are the part numbers of these?

      I'd like a picture of the monitor showing all the boards in place and the cables linking them.

      PlainBill
      Attached Files
      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


        #4
        Re: Sceptre X20G NAGA-II no power

        Thanks for all the information! I will complete the tasks you laid out for me to do as soon as I get off work this afternoon and will post the results. thanks again.
        “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

        Comment


          #5
          Re: Sceptre X20G NAGA-II no power

          Got my tasks completed. The part numbers mid right of the ps board are as follows I also marked on the picture where D107 and U105 are located.
          D107= PEC 503
          ER1002FCT
          U105= L7805CV
          WCC1A0346
          MOROCCO
          I also have the part number from the other heatsink mounted parts if needed later, I did not want to flood you with information you did not need or ask for.

          The LDO regulator part number is the same for all 5 components
          part# 4DH 17-33. And the readings are
          U9= (1) 0 (2) 3.3V (3) 5.3V
          U22= (1) 0 (2) 3.3V (3) 5.3V
          U27= (1) 0 (2) 3.3V (3) 4.9V
          U20= (1) 0 (2) 3.3V (3) 5.3V
          U21= (1) 0 (2) 3.3V (3) 5.3V

          Switching regulator part numbers are both the same.
          JM46AB
          LM25765
          -ADJ P+

          Hope this helps please let me know if you need any more information. Also keep in mind I'm taking these pics with my iphone, the wife lost the charger for our good cam . if you need better pics I will buy a new charger just let me know.
          Attached Files
          “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

          Comment


            #6
            Re: Sceptre X20G NAGA-II no power

            Originally posted by sabre504 View Post
            HI have you checked for voltage on the large Filter ?

            In case you dont know but sure you do test this in dc mode Red + black -
            and you should see about 165-170 volts
            thanks for the reply I checked the filter and I'm getting 217V
            “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

            Comment


              #7
              Re: Sceptre X20G NAGA-II no power

              Originally posted by aftonr View Post
              The LDO regulator part number is the same for all 5 components
              part# 4DH 17-33. And the readings are
              U9= (1) 0 (2) 3.3V (3) 5.3V
              U22= (1) 0 (2) 3.3V (3) 5.3V
              U27= (1) 0 (2) 3.3V (3) 4.9V
              U20= (1) 0 (2) 3.3V (3) 5.3V
              U21= (1) 0 (2) 3.3V (3) 5.3V
              Note the suffix in the part number denotes the correct output voltage. So all your regulators above are good.

              Switching regulator part numbers are both the same.
              JM46AB
              LM25765
              -ADJ P+
              Datasheet is at

              http://pdf1.alldatasheet.com/datashe.../LM2576-5.html

              Now measure the DC voltage of each of the 5 pins with respect to ground. I normally put my black probe on a screw on the logic board for ground. Report all readings for all chips.
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              Comment


                #8
                Re: Sceptre X20G NAGA-II no power

                Originally posted by aftonr View Post
                thanks for the reply I checked the filter and I'm getting 217V
                217V???

                Are you measuring DC voltage across the legs of the large filter capacitor? Black probe on negative and red probe on positive leg of the capacitor?

                Warning this is high voltage.
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                Comment


                  #9
                  Re: Sceptre X20G NAGA-II no power

                  Originally posted by retiredcaps View Post
                  217V???

                  Are you measuring DC voltage across the legs of the large filter capacitor? Black probe on negative and red probe on positive leg of the capacitor?

                  Warning this is high voltage.
                  Actually I was using a ground screw and got that reading. I rechecked it with your direction and got 394.4 V DC
                  “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

                  Comment


                    #10
                    Re: Sceptre X20G NAGA-II no power

                    Now measure the DC voltage of each of the 5 pins with respect to ground. I normally put my black probe on a screw on the logic board for ground. Report all readings for all chips.
                    Here are the results attached pic with how I labled the pins.

                    Q4= (1) 8.84 V
                    (2) 2.5 V
                    (3) 0
                    (4) 1.22 V
                    (5) 0

                    Q11= (1) 12.52 V
                    (2) 5.0 V
                    (3) 0
                    (4) 1.22 V
                    (5) 0
                    Attached Files
                    “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

                    Comment


                      #11
                      Re: Sceptre X20G NAGA-II no power

                      Originally posted by aftonr View Post
                      Actually I was using a ground screw and got that reading. I rechecked it with your direction and got 394.4 V DC
                      If you are in Missouri USA, then this implies that this monitor uses some sort of PFC.

                      http://en.wikipedia.org/wiki/Power_factor

                      Normally, we expect 120AC x 1.414 = 170V DC. With PFC, that DC voltage gets boosted up well over 300V DC.
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                      Comment


                        #12
                        Re: Sceptre X20G NAGA-II no power

                        Wait a minute, the actual part number is LM2576S, not ML25765 (now that I see the close up photo of Q11). Correct datasheet is at

                        http://pdf1.alldatasheet.com/datashe...H/LM2576S.html

                        With the -ADJ in the part number, I *think* Q4 and Q11 are good based on the output voltages on pin 2.
                        Last edited by retiredcaps; 02-29-2012, 09:36 PM.
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                        Comment


                          #13
                          Re: Sceptre X20G NAGA-II no power

                          Here is the close up of Q4
                          Attached Files
                          “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

                          Comment


                            #14
                            Re: Sceptre X20G NAGA-II no power

                            thanks for the replies and links its good information I'm always up to learn something new. do you know of anything else I can check..
                            “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

                            Comment


                              #15
                              Re: Sceptre X20G NAGA-II no power

                              This monitor does have a PFC front end which seems to be working.

                              The voltages on the LDO regulators are all fine, the buck regulators are also reasonable, but my question is why is there no 1.8 volts?

                              Other than hoping I could see something with a better picture of the signal board, I can't think of any further steps.

                              PlainBill
                              Last edited by PlainBill; 02-29-2012, 09:54 PM.
                              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


                                #16
                                Re: Sceptre X20G NAGA-II no power

                                Here is a few pics of the signal board you requested I gave an overview shot and two close up pics of the top and bottom half of the board.
                                Attached Files
                                “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

                                Comment


                                  #17
                                  Re: Sceptre X20G NAGA-II no power

                                  also I noticed that the green LED "circled red" is the only light that comes on and it is a very faint light that blinks slowly. the other LED next to it does not even come on. I didn't know if this would tell you something. The 2 wires that feed this board go to the ps.
                                  Attached Files
                                  “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

                                  Comment


                                    #18
                                    Re: Sceptre X20G NAGA-II no power

                                    Originally posted by PlainBill View Post
                                    This monitor does have a PFC front end which seems to be working.

                                    The voltages on the LDO regulators are all fine, the buck regulators are also reasonable, but my question is why is there no 1.8 volts?

                                    Other than hoping I could see something with a better picture of the signal board, I can't think of any further steps.

                                    PlainBill
                                    I just wanted to update my progress with this monitor. I gave up on this project and put it back together to store it away. and after I was done putting it back together I thought I would plug it in to see if it would work just wishful thinking but to my surprize it came on ... I dont know why it wouldn't come on when I plugged it in during tests? but I'm not going to complain it is just very puzzling to me. I'm thinking the switching transistor I replaced must have been the problem but why I couldnt get it to respond when the casing was off is a mystery to me..
                                    “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

                                    Comment


                                      #19
                                      Re: Sceptre X20G NAGA-II no power

                                      Originally posted by aftonr View Post
                                      but to my surprize it came on
                                      You are 2nd person within the last 36 hours to experience that.

                                      https://www.badcaps.net/forum/showthread.php?t=19354
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                                      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


                                        #20
                                        Re: Sceptre X20G NAGA-II no power

                                        this may be a stupid question but there was a plate that was screwed on across the 2 heatsinks on the ps board I had this off during tests I just assumed it was there for thermal reasons.. am I right about this or was this some kind of ground??
                                        “Be Who You Are and Say What You Feel Because Those Who Mind Don't Matter and Those Who Matter Don't Mind.”

                                        Comment

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