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    samsung lnt3232hx - black screen, audio ok

    i have a samsung lnt3232hx, 32" lcd 720p tv. when turned on there is no light or flicker onscreen, just black screen, yet audio is ok. i tested the 2 hdmi, 2 composite, svideo, and coax inputs with the same black screen resulting, and persisting when changing video source. i tried leaving the tv on for about 90 minutes, with audio up enough to tell its still going, but there were no changes. no edge lights, no lights with the back off other than the red power light and the digital audio port. i inspected the main (only ceramic caps), p/s (samwha & capxcon caps) & inverter (brown, no visible company identifier) caps & cables but didnt see any apparent problems.

    i have replaced bad caps on another pc monitor, but these caps show no bulging, discoloration & all the boards i looked at were quite clean looking with no cold solder joints visible. i tried to remove the cover of the tcon bd, but after taking out the 4 screws (yes, i unscrewed the braces above), the covers will only slide side-to-side a bit, but won't lift out - must be a trick that i just dont see to remove it. so i was unable to inspect tcon bd.

    the slow-blow fuse on the p/s tested with 1 ohm resistance. i need to find my magnifier to see where any tiny fuses might reside on the boards. i disconnected the inverter bd cable to test voltage - the 24v measured 24.4, 5v = 5.3, and another wire measure 1.9 - the grounds all had 1 ohm resistance between them. the leads to the main board had 5 = 5.3 & 12 = 11.8. i noted that when i disconnected the cables between the p/s & main, there was no voltage to the inverter (which i expect is normal)

    in my reading, someone noted that samsung uses cheap panels by chunghwa instead of their own, which is the case with this tv. i disconnected and reconnected all the cables that werent glued in place. i dont know the history of the tv, as it was left behind by a freeloading ex-roommate. if i can fix it within reason, i would find some satisfaction.

    are there other troubleshooting suggestions i could try? do these symptoms point to anything common or obvious to the expert? what's the trick to remove the cover above the tcon bd? thanks for any and all help
    Last edited by gb77; 08-31-2011, 02:09 AM.

    #2
    Re: samsung lnt3232hx - black screen, audio ok

    Probably an inverter problem.

    One of the things that strikes me about your account is it reads like a someone wandering around aimlessly looking for a cause rather than logically analyzing the problem.

    1. You have sound. That means the power supply is PROBABLY good; certainly the majority is good.

    2. The screen is black. Do you get anything when you hit the menu button, change channel, or select a different input? No - that means the problem is not input related.

    3. You do not see any signs of light, other than the front panel light. There is ALWAYS some light leakage from the panel on CCFL backlit sets. As a matter of fact, that should have been your first observation.

    4. You neglected the obvious step of shining a bright light on the panel to see if a faint image is visible.

    5. You neglected to provide pictures.



    PlainBill
    Last edited by PlainBill; 08-31-2011, 06:25 AM.
    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
      thanks for the reply PlainBill, i'll reply to items 3-5

      3 - right, i'm not seeing any light/leakage at all around the panel. on or off it looks the same even in a room with all the lights out.

      4 - i do see the image when i shine a flashlight against the screen

      5 - i can see that pics of the tcon cover would be helpful, but i'm not sure if pics of the board or other things can help - please let me know. so here are some pics around the cover.

      from the top, showing 4 screws removed, and nothing else seeming to hold the cover in place from above

      from bottom

      zoom of top corner


      if it seems the inverter is the issue, are there additional tests i can try to see if its something i might fix, or? i have a multimeter, but i might have a friend with a fluke to lend. thanks again.
      Attached Files

      Comment


        #4
        Re: samsung lnt3232hx - black screen, audio ok

        Originally posted by gb77 View Post
        thanks for the reply PlainBill, i'll reply to items 3-5

        3 - right, i'm not seeing any light/leakage at all around the panel. on or off it looks the same even in a room with all the lights out.

        4 - i do see the image when i shine a flashlight against the screen

        5 - i can see that pics of the tcon cover would be helpful, but i'm not sure if pics of the board or other things can help - please let me know. so here are some pics around the cover.

        from the top, showing 4 screws removed, and nothing else seeming to hold the cover in place from above

        if it seems the inverter is the issue, are there additional tests i can try to see if its something i might fix, or? i have a multimeter, but i might have a friend with a fluke to lend. thanks again.
        DON'T WORRY ABOUT THE TCON!!! It's not the cause of your problem. Put the screws back in and forget you ever worried about it.

        Remember, I don't have your TV, the same model TV, or even a picture of the back of a TV like yours. If you want me to help you, I will need a picture of the back of the TV, and another of the inverter. Make them both at least 1000 x 1000 pixels so I can see as much detail as possible.

        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


          #5
          ok here is the back full view

          the left side of inverter

          center

          right


          i found f1, f2 & f3 towards the center, which i would guess are fuses. 1 & 2 check out with 1 ohm resistance, while 3 ( D ) is open/bad, or i'm not getting good contact from the top or sides.

          if some detail, better focus, or less glare is needed let me know, i can try again - thanks for your help
          Attached Files
          Last edited by gb77; 08-31-2011, 10:30 PM.

          Comment


            #6
            Re: samsung lnt3232hx - black screen, audio ok

            Originally posted by gb77 View Post
            ok here is the back full view

            the left side of inverter

            center

            right


            i found f1, f2 & f3 towards the center, which i would guess are fuses. 1 & 2 check out with 1 ohm resistance, while 3 ( D ) is open/bad, or i'm not getting good contact from the top or sides.

            if some detail, better focus, or less glare is needed let me know, i can try again - thanks for your help
            Heck, you are doing most of the hard work!!! You have a tendency to veer off at tangents, but you have already identified the important symptoms.

            Obviously, F3 open is the problem. We don't want to simply short across it without determining WHY it is open. What IS encouraging is that F1 and F2 are the fuses for the drivers. I had expected to tell you that you would have to replace some of the power FETs. This might be much easier.

            The D on F3 seems to indicate it is a .250 Amp fuse.

            1. What is the resistance from the upper end of F3 to ground? I want to see if there is a 'hard' short on the power rail.

            2. You may have already done so, but what is the voltage on the VBL pins of the connector?

            3. If you don't find any obvious bad parts I'm going to need clearer pictures of the center section of the inverter. I can't see just how much area this fuse supplies.

            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


              #7
              Re: samsung lnt3232hx - black screen, audio ok

              1. F3 upper/lower both test as open, no short (same as F1 & F2)
              2. not sure which are VBL pins since only 1 pin on p/s is labeled BL - here are pins (left to right in center pic) - p/s label / voltage - tested same on either end of cable

              24V--24V--24V--24V--24V--GND-GND-GND-GND-GND-NC--BL--ADIM-PWM
              24.4--24.4-24.4-24.4-24.4---0----0----0----0----0--0---5.3--2.8---0

              F1,2,3 all have 24.4v going thru them, with F3 measuring 0 at the top.

              3. here's a clearer pic of the center

              doing a check with multimeter shows F3 goes to the right - thru R131,61 & 62 (1 Ω bottom, 14 top for 131 & 61, while 62 is open on top - bad? label is 332). R60,59 measure 14 on bottom, 28 on top. then to the center pin of Q17 is 28 (label is C5076 / 5M). the only other continuity from F3 i found was the copper dot below R60 @ 1 Ω & the dot above R61 @ 14.

              is the amber (flux?) residue on some of the pins of the large sockets at the top of the board anything to worry about? or just some crispy residue left from manufacturer?
              Attached Files
              Last edited by gb77; 09-01-2011, 09:57 AM.

              Comment


                #8
                Re: samsung lnt3232hx - black screen, audio ok

                did some more poking around - hopefully it will help.

                the top of R62 goes to the copper dot above & the bottom pin of Q17 @ 1 Ω. the top pin of Q17 goes to the top of R65,C62,C61,C67,C9 & top left pins (pin2?) of U4 & U5 @ 1 Ω. it also goes to the center pin of Q18 & bottom pin of R42 @ 1 Ω (also labeled 332, and open to the top). the top of R42 has 1 Ω to the top right pin of Q18. top left of Q18 continues thru C64,C63 & R11. let me know of any other checks i might do.

                i've doctored this foto a bit to make it more apparant that there is some darkening/burning of one side of the inverter backing. the back of the board is clean & shiny. something to worry about?


                and sorry i didnt see that 24V from p/s = VBL on inverter until now when its too late to edit my last post.
                Attached Files
                Last edited by gb77; 09-01-2011, 11:35 AM.

                Comment


                  #9
                  Re: samsung lnt3232hx - black screen, audio ok

                  I've uploaded a picture with some points I would like checked.

                  1. F3 - could you either measure it or lay a ruler next to it? I want to be sure I am suggesting the correct replacement.

                  2. Note the red and black lines I have drawn on CN1. The red line indicates the pins labeled VBL, the black the pins labled Gnd. Note the table to the right of CN1

                  3. What is the resistance from the upper end of F3 (blue dot) to Gnd?

                  4. The brown line indicates the separation between the area powered through F3 and Gnd. How far does the area powered buy F3 extend?

                  5. Do you have a resistor in the 100 ohm range?

                  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


                    #10
                    Re: samsung lnt3232hx - black screen, audio ok

                    did u see the 2 posts above yours that describe what i found with the multimeter (no power of course)? i was editing them along the way, so we might have crossed timing a bit. should i continue to follow around (U4, U5, Q18) to see how far they go until i cant find anything more?

                    1. about 1/8x1/16" or 32x16mm

                    2. yup, i got that & all VBL = 24.4v

                    3. infinite - open

                    4. R131,61,62 bottom are the only points i found with <1Ω. then the circuit goes to R59&R60, then to Q17 where continuity to F3 ends. R1,C56,U2 etc have no continuity to F3

                    5. i have a couple that test @ 102Ω

                    Comment


                      #11
                      Re: samsung lnt3232hx - black screen, audio ok

                      Try hooking the 100 ohm resistor across F3, then measuring voltage drop across that resistor. Apply power only briefly, it could get quite hot.

                      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


                        #12
                        Re: samsung lnt3232hx - black screen, audio ok

                        tested twice - both times voltage only drops to 24.3 in a couple seconds while the panel lights up (hooray)

                        Comment


                          #13
                          Re: samsung lnt3232hx - black screen, audio ok

                          Originally posted by gb77 View Post
                          tested twice - both times voltage only drops to 24.3 in a couple seconds while the panel lights up (hooray)
                          Great!! This appears to be a Littlefuse 466 type fuse, available from DigiKey as their number F1452CT-ND at $.83 each. They only have 14,728 on hand.

                          PainBill
                          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 lnt3232hx - black screen, audio ok

                            ok, thanks - since you're not offering further comments, are you thinking this could be a one time event, and if it wasn't you will respond to whatever happens when it happens? i appreciate your help, and dont expect you to talk about every possibility.

                            is there a qualitative difference in fuses that i need to worry about? there is a nearby surplus store with lots of fuses (same place i got the resistors). tomorrow i could solder in a glass or wired pico .250A 125V fast fuse if i dont find a proper surface mount from there, & see if the tv will provide joy over the weekend before ordering from digikey.

                            thanks again for your time and help

                            Comment


                              #15
                              Re: samsung lnt3232hx - black screen, audio ok

                              Originally posted by gb77 View Post
                              ok, thanks - since you're not offering further comments, are you thinking this could be a one time event, and if it wasn't you will respond to whatever happens when it happens? i appreciate your help, and dont expect you to talk about every possibility.

                              is there a qualitative difference in fuses that i need to worry about? there is a nearby surplus store with lots of fuses (same place i got the resistors). tomorrow i could solder in a glass or wired pico .250A 125V fast fuse if i dont find a proper surface mount from there, & see if the tv will provide joy over the weekend before ordering from digikey.

                              thanks again for your time and help
                              If you can pick up a 250 ma fuse locally, by all means do so. If you can find a picofuse, I'd be tempted to butcher it in and leave it, a purist would of course install only a .250A SMD fuse purchased from an authorized Samsung parts distributor.

                              While I might be tempted to leave the resistor in place over the weekend, I'd say go with a picofuse, a pigtail fuse, or even a .25A fuse in a holder.

                              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


                                #16
                                Re: samsung lnt3232hx - black screen, audio ok

                                thanks again PlainBill - couldnt find any small fuses so i "butchered it in" - soldered a fuse holder to the ends of F3 and dangled it outside the cover - holder & 4 fuses for 2 bux! been working fine for a few hours now.

                                but ... the lcd has a shadow - not noticeable in bright/dark but at mediums..


                                is this an aging spot on a 4yr old lcd that will slowly die (i dont mind it much since its in a corner, and less than 2% of the screen), or something that can be fixed (for 3 bux maybe ;o) .. )? if fixable, should i start a new thread? thanks for any comments
                                Attached Files

                                Comment


                                  #17
                                  Re: samsung lnt3232hx - black screen, audio ok

                                  That is strange, it seems to be too intense to be a bruise. I'm not sure what else if could be.

                                  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

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