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    Dynex DX-46L150A11 backlight/inverter problem?

    I was given a 46" Dynex that would light up for 10 to 30 seconds then go dark. Sound works find and there's no whining/buzzing sound coming from anything.

    I fixed a 21" monitor about a year ago with a kit from here so I thought I'd start with the caps on the TV. Nothing looked obvious and all the voltages tested good even under load.
    I replaced all the large caps on the inverter for the heck of it but no change.

    So, researching on the forum I discovered other things that usually go wrong with Darfon inverters. All the fuses and transformers tested ok. With a sugestion from a thread to look at it in a dark room I discovered one of the 12 lights wasn't working.

    I thought I could swap which transformer and circuit was powering which lamp by unsoldering the HV lead and associated ceramic cap and jumpering to the next lamp. In essence I wanted to swap the outputs of an adjacent transformer to see if the suspect lamp would light. The result was the '2 seconds to black' and I think the suspect lamp is still dark (goes off to quickly to really tell). So I remove the jumpers and put everything back and I get almost 30 seconds of light again with the suspect lamp being dark.

    Now, a used inverter is $20 on ebay and with the $9 for the caps already spent, $30 would be a good price if it would work. Thing is with the one bulb being dark it could be the bulb and not the inverter. At which point it might not be worth fixing (see p.s.)
    How can I test the bulb or bulbs before buying an inverter?
    I'm open to other suggestions.
    Thanks for looking,
    davidk

    Dynex DX-46L150A11
    Display T460HW03 VF
    Inverter - Darfon V291-5xx , 4H+V2918.061 /B
    Chip on the inverter is OZ9937GN
    Power supply # 569KS0720A 2009.12.18
    Main board # 569KS0169C

    p.s. I've seen bulbs for sale various places and actually replaced two on my laptops. But with 12 bulbs and only one new one wouldn't the color difference be a bit much.
    I've seen 1000mm bulbs for $25. Replace them all and that's $300. A bit much for a free TV for my son.
    Attached Files

    #2
    Re: Dynex DX-46L150A11 backlight/inverter problem?

    Two ways to check it out. Perhaps, swap the bad bulb around with a good one. Check voltages after the inverter transformer, the hole on the white tracer. The pic looks like there's a spot for you to check with the meter. Watch out, high voltage. Also, check the 24v pin on the power supply connector to make sure you're getting 24v. In which it appears your are. If there is a blown bulb, just replace the one. It's could be blown from a shorted transformer or circuit while the others are fine. It appears to be the inverter board. But if you can replace the board and perhaps one bulb, it's a great picture. Well worth the 30 bucks. There are more experienced here that could help you out better than I can. Just got done fixing a 42 Dynex that had a t-con problem. Love it.

    Comment


      #3
      Re: Dynex DX-46L150A11 backlight/inverter problem?

      Do not try to check the HV output of the inverter transformer, the firing voltage is about 2000V, and about 800~1000V for running voltage, you will badly damage your meter.
      I would check the resistance of the high voltage winding side of the transformers to make sure they are OK. The inverter circuit will shutdown if it detect if any one of the lamp is not connected, or if any one of the lamp draws too much current, you will get 2-second to black.
      Can you read the P/N on the inverter transformers?
      Check the resistance (2K Ohm scale) on
      1& 2 =
      1& 3 =
      Attached Files
      Last edited by budm; 08-13-2013, 11:35 PM.
      Never stop learning
      Basic LCD TV and Monitor troubleshooting guides.
      http://www.badcaps.net/forum/showthr...956#post305956

      Voltage Regulator (LDO) testing:
      http://www.badcaps.net/forum/showthr...999#post300999

      Inverter testing using old CFL:
      http://www.badcaps.net/forum/showthr...er+testing+cfl

      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
      http://s807.photobucket.com/user/budm/library/

      TV Factory reset codes listing:
      http://www.badcaps.net/forum/showthread.php?t=24809

      Comment


        #4
        Re: Dynex DX-46L150A11 backlight/inverter problem?

        Thanks guys,
        I had checked all the transformers and they all read about the same. In-circuit readings fluctuated a bit so I removed a few including the suspect one and they all read the same. The two leads on the bottom left are the primary with 1 and 3 the secondary. With it out there was no continuity to 2 or any wire soldered to it that I could tell.

        When I jumpered things I ignored terminal 2 because it didn't seem to be connected internally. I'm going to try again this time cutting the trace that goes to the lamp and jumper it with a different one. If I can get it to exhibit the same '30 seconds on' with power to the bulbs swapped it should tell me if the bulb is actually dead.

        To me it seems weird that it would light for 30 seconds, then with things swapped only give 2 seconds. What I'm trying to do makes sense, right? All the circuits look the same for each bulb so I should be able to move the HV output to different bulbs and
        still have it work.

        Let's assume that the bulb is bad. Could the detection part of the circuit be bad such that when hooked up to a different transformer and circuit it would immediately shut down instead of lighting for 30 seconds?

        More things to test when I get home from work, whoo hoo!
        Thanks again,
        davidk

        Comment


          #5
          Re: Dynex DX-46L150A11 backlight/inverter problem?

          Well, it's definatily a bad bulb.
          I cut the traces that go to two bulbs and swapped them and the unlit bulb didn't move. Inverter is good.
          So, the only thing to do is disassemble the display panel.

          Taking it apart was easy enough...I just really hate touching the actual display panel (finger prints and all. OK, I have issues)
          You can see in the pic the bad bulb. You can also see that the plastic reflectors are pretty crispy (I can paint or put some foil on them). They should be white and you could actually see that in the display.

          So, given that one bulb is bad how long before the others go too? And if one is replaced, wont it's color be brighter than the others? The bulbs dimm over time till they die.
          This was my mother-in-laws set and she never really turned it off so if I had to guess, the bulbs have 10k to 15k hours on them. They're about done arent they?

          CFLWarehouse.com has them for $20 which is $240 for the set. Think it's worth it? Or just replace one, get a little more life from it and stop worring about stuff?

          What do you think?
          Thanks,
          davidk
          Attached Files
          Last edited by davekra; 08-14-2013, 05:10 PM.

          Comment


            #6
            Re: Dynex DX-46L150A11 backlight/inverter problem?

            You can tell when the bulb is getting old, you will see blackened ends, and when it is really bad, it will glow pinkish or red hot at the tube ends of the lamp.
            http://s807.photobucket.com/user/bud...?sort=3&page=1
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #7
              Re: Dynex DX-46L150A11 backlight/inverter problem?

              Well, I'd love to order a set of lamps and have another 'FIXED' in my column but the CFO has denied my budget request.

              All the lamp ends are pretty black. I might just order one lamp and see just how long the others last.
              Or I could make up a big matrix of led's and use something to do local dimming

              Seems such a shame to throw something thats repairable away...but then that's the society we live in.

              Thanks for your help and quick responses.
              davidk

              Comment


                #8
                Re: Dynex DX-46L150A11 backlight/inverter problem?

                hello there I have the same model with the same problem. Do you know what size the diameter and length on the bulb? I need to order bulbs but I am not sure how to go about figuring out the bulb diameter. Any advise would be much appriciated.

                Comment


                  #9
                  Re: Dynex DX-46L150A11 backlight/inverter problem?

                  Hey guys, I just acquired this exact same set with a very similar problem, and was trying to get her going again. My set will actually turn on and stay on for anywhere from 30 seconds to 10 minutes before going the screen goes black (average "on-time" is about 1.5-2 minutes). The picture looks fine during this time, and I can access all menus and inputs without issue. The indicator light stays blue - showing that its still on, and sound still works fine. I did the 'flashlight to the screen' check and can still see a picture in the blackness. If I switch the tv off, and back on again, it will again work for another few minutes before going black again. I can't see any bad caps, or burnt components right off the bat. I am thinking its an inverter board issue, but would like some input on what to check or look for. Thanks

                  Comment


                    #10
                    Re: Dynex DX-46L150A11 backlight/inverter problem?

                    Although I gave the set away before it was fixed it turned out to be the lamps not the inverter.
                    Do you know how long the set has been on?
                    In a room with the lights on the set looked good for the 30seconds it was on, but in a dark room you could clearly see one of the lamps wasn't lit.
                    Before spending money on an inverter take it apart to look at the lamps.
                    If the ends are blackened you may be looking at new lamps instead of an inverter.
                    I was able to rewire the output of the inverter (esentally swapping the lights around) to determine the lamp that wasn't lighting was indeed the problem and not the inverter.
                    If it is actually the inverter there are some continuity checks you can do to the HV transformers to determine if one of them is the problem, other than that I don't know.

                    Good luck

                    Comment


                      #11
                      Re: Dynex DX-46L150A11 backlight/inverter problem?

                      ^^^^^^^^^^^^^^

                      Lots of excellent tips there - I would try the trying to see a bulb out in the dark room
                      Please upload pictures using attachment function when ask for help on the repair
                      http://www.badcaps.net/forum/showthread.php?t=39740

                      Comment


                        #12
                        Re: Dynex DX-46L150A11 backlight/inverter problem?

                        It will be good if more people can do the one lamp probe like I did to see if that trick will work for lots of people or not to help find bad inverter output.
                        Never stop learning
                        Basic LCD TV and Monitor troubleshooting guides.
                        http://www.badcaps.net/forum/showthr...956#post305956

                        Voltage Regulator (LDO) testing:
                        http://www.badcaps.net/forum/showthr...999#post300999

                        Inverter testing using old CFL:
                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                        http://s807.photobucket.com/user/budm/library/

                        TV Factory reset codes listing:
                        http://www.badcaps.net/forum/showthread.php?t=24809

                        Comment


                          #13
                          Re: Dynex DX-46L150A11 backlight/inverter problem?

                          Budm I have read it a couple of times a few members seem to have tried it with no result.
                          I may have missed it as I was awol when you first introduced it but I think a few points need more explanation for us learners.
                          For example these are the types of questions - do you leave the existing bulbs connected and do you unplug the ones from the inverter being tested?
                          Do you touch the bulb on a secondary winding post?
                          If the transformer is good presumably the lamp will glow? flash?
                          If the transformer is bad will there be nothing?

                          I would have thought all lamps connected but as we are testing for them going off it is a case of testing on each post immediately on switch on and the bulb will flash for the very short time that the panel flashes unless a transformer is bad then it wont flash on that post?

                          Basically I need something short and to the point to tell those doing the test what to expect.

                          Also I wondered if you could add it to your signature AND perhaps just link to your original
                          post - the first one is getting a bit long

                          https://www.badcaps.net/forum/showpo...68&postcount=1

                          https://www.badcaps.net/forum/showpo...27&postcount=1
                          Last edited by selldoor; 07-31-2014, 03:08 PM.
                          Please upload pictures using attachment function when ask for help on the repair
                          http://www.badcaps.net/forum/showthread.php?t=39740

                          Comment


                            #14
                            Re: Dynex DX-46L150A11 backlight/inverter problem?

                            "do you leave the existing bulbs connected" Yes.
                            "Do you touch the bulb on a secondary winding post?" Yes.
                            What I look for is if all the output will light up the test lamp at the same brightness, the one test point that does not will be the one to suspect as bad, as you can see that the bad one in my post the lamp lights up dimly. I did not run into any inverter with bad transformer since I made this probe to use this method to find out if it is useful or not.
                            I also use to verify if the inverter even fire up at all for second or not instead of trying look the holes in the back of the LCD panel.
                            Using it on the inverter with just one transformer instead of many transformer for each lamp will not help much, it will only indicate you do have high voltage or not, it is good for multiple transformer type inverter.
                            Never stop learning
                            Basic LCD TV and Monitor troubleshooting guides.
                            http://www.badcaps.net/forum/showthr...956#post305956

                            Voltage Regulator (LDO) testing:
                            http://www.badcaps.net/forum/showthr...999#post300999

                            Inverter testing using old CFL:
                            http://www.badcaps.net/forum/showthr...er+testing+cfl

                            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                            http://s807.photobucket.com/user/budm/library/

                            TV Factory reset codes listing:
                            http://www.badcaps.net/forum/showthread.php?t=24809

                            Comment


                              #15
                              Re: Dynex DX-46L150A11 backlight/inverter problem?

                              Thanks Budm I edited after you posted - how about adding it to your signature?
                              Please upload pictures using attachment function when ask for help on the repair
                              http://www.badcaps.net/forum/showthread.php?t=39740

                              Comment


                                #16
                                Re: Dynex DX-46L150A11 backlight/inverter problem?

                                I added the info on #14 to this one:
                                https://www.badcaps.net/forum/showth...l261a12&page=2
                                Never stop learning
                                Basic LCD TV and Monitor troubleshooting guides.
                                http://www.badcaps.net/forum/showthr...956#post305956

                                Voltage Regulator (LDO) testing:
                                http://www.badcaps.net/forum/showthr...999#post300999

                                Inverter testing using old CFL:
                                http://www.badcaps.net/forum/showthr...er+testing+cfl

                                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                http://s807.photobucket.com/user/budm/library/

                                TV Factory reset codes listing:
                                http://www.badcaps.net/forum/showthread.php?t=24809

                                Comment


                                  #17
                                  Re: Dynex DX-46L150A11 backlight/inverter problem?

                                  Originally posted by davekra View Post
                                  Although I gave the set away before it was fixed it turned out to be the lamps not the inverter.
                                  Do you know how long the set has been on?
                                  In a room with the lights on the set looked good for the 30seconds it was on, but in a dark room you could clearly see one of the lamps wasn't lit.
                                  Before spending money on an inverter take it apart to look at the lamps.
                                  If the ends are blackened you may be looking at new lamps instead of an inverter.
                                  I was able to rewire the output of the inverter (esentally swapping the lights around) to determine the lamp that wasn't lighting was indeed the problem and not the inverter.
                                  If it is actually the inverter there are some continuity checks you can do to the HV transformers to determine if one of them is the problem, other than that I don't know.

                                  Good luck
                                  The one good thing is that I have a few minutes to inspect the set as it does not turn off right away. I will re-inspect the lamps with the lights off to see if I can find a bad lamp. In one of the earlier posts, someone asked to check the resistance on the transformer from pins #1 to 2, and #1 to 3. I was only getting a value on pins 1 to 3. All 12 transformers showed no readings on pins 1 to 2, EXCEPT transformer #12, which showed 0 ohms, but that's because it looks like the points are connected via a trace... so I'm confused.

                                  Comment


                                    #18
                                    Re: Dynex DX-46L150A11 backlight/inverter problem?

                                    Perhaps they didnt know which pins were for the secondary windings.
                                    So with meter on 2000 ohms what did you get on 1 to 3?
                                    If you have a houshold cfl bulb you could try budms trick above.
                                    If you can it would be really helpful to us
                                    Please upload pictures using attachment function when ask for help on the repair
                                    http://www.badcaps.net/forum/showthread.php?t=39740

                                    Comment


                                      #19
                                      Re: Dynex DX-46L150A11 backlight/inverter problem?

                                      Using Budm's picture from post #3, I was able to get a reading of around ~800 ohms between pins #1 and 3. this was pretty consistent across all 12 transformers.

                                      If you look at Davekra's very first picture in post #1, you can see the very last transformer on the right has a trace connecting pins 1 and 2. Testing pins #1 and 2 give no readings (meter stays on 1 ohm which is the default reading) on the first 11 transformers, except #12 which it then shows 0 (zero) ohms.

                                      I'm reading up on budms trick with the cfl bulb. If I'm looking at this correctly, you only need to use 1 wire (Is there a second wire needed at all?). Solder that wire to the bottom lead of the cfl bulb, and then connect that to the output post of the transformer? Good transformer=fully lit bulb, bad transformer=dimly lit bulb... Also, using budms pic in post #3, where exactly do I touch the wire to to make these tests with the cfl? Thanks guys.
                                      Last edited by Big Jugs; 08-01-2014, 12:04 PM.

                                      Comment


                                        #20
                                        Re: Dynex DX-46L150A11 backlight/inverter problem?

                                        Thought I had replied last night ??? anyway
                                        IF the pins 1 and 2 on the last transformer are connected by a trace then that is factory
                                        so is likely good if they are not connected by the trace you may need to remove from the board to see why it is shorted.

                                        Yes screw in bulb - solder a fairly sturdy wire to the bottom centre pin.

                                        You dont need to permanently connect it - just touch it on a secondary post - PIN 1
                                        in this case.

                                        With is all connect (including the bulbs) touch along all the "1" pins

                                        Yes bright =good Dim = more testing

                                        I was rather hoping you would spot a weak lamp.
                                        Please upload pictures using attachment function when ask for help on the repair
                                        http://www.badcaps.net/forum/showthread.php?t=39740

                                        Comment

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