Vizio vx42l troubleshooting help.

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  • noonehere
    New Member
    • Apr 2012
    • 6
    • usa

    #1

    Vizio vx42l troubleshooting help.

    I picked this monitor up as part of my ongoing quest to teach myself electronics. Near as I can tell, it was the victim of a botched repair.

    First problem it had, was it would go into standby when power was applied. The vizio logo would light amber, then when you pushed the power button, it would go white. You could hear the power supply kick on, but that was all that would happen. I would then have to unplug it to get it to "turn off." After some google searching I found several threads here about regulators on the mainboard. I tested the u33 LDO which was, in fact, bad. Replaced that:

    Then it would power on, and I could get sound. When shining a flashlight through the screen, I could see picture. Ok, backlight time. I cleaned up some horrific soldering botch on both boards, and they are still ugly. Visually the driver chip on the slave board had a pin fried, and I could tell both driver chips had been changed, as they both had flux puddles and pulled up traces. Replaced the driver chip on the slave board, and used a silver pen to re-draw the traces for the driver chips (red boxes in the inverter pics)

    Now, the backlight will power on for about 1-2 seconds, then will turn off. The tubes do not look like they are igniting all the way, as the center of the display never comes to full brightness. Still have sound and picture (with flashlight) The HV transformers all test ok on my multi meter, and none of the caps look like they are bad from the outside.

    Also, the two heatsinks on the powerboard that are circled in red. They are energized (both when on, and when in standby) with 65v ac. That was a bit of a painful discovery. That cannot be normal right? I do not know if they've always been charged; I only got zapped during testing, after re-installing the inverter boards.

    My question is, what should I look at next? Does it sound like bad ccfl's? All the tubes seem to be doing the same thing, and I do not have a spare set of inverters to test with. (unless I could use the darfon board from an insignia I have apart)

    P.S. Anyone know what that 4pin ribbon cable by the master inverter board is?(circled in red) There are traces for a plug on the board, but no plug.
    Attached Files
  • retiredcaps
    Badcaps Legend
    • Apr 2010
    • 9271

    #2
    Re: Vizio vx42l troubleshooting help.

    Originally posted by noonehere
    I picked this monitor up as part of my ongoing quest to teach myself electronics.
    1) I started learning electronics by fixing old broken lcd monitors.

    After some google searching I found several threads here about regulators on the mainboard. I tested the u33 LDO which was, in fact, bad.
    2) Thanks for doing some research first. Lately, we have had a flood of people who don't research, don't use punctuation or paragraphs, and can't or won't follow directions about uploading pictures.

    Now, the backlight will power on for about 1-2 seconds, then will turn off.
    3) 2 seconds to black can be

    a) bad caps
    b) bad ccfls
    c) bad ccfl wiring (especially the return wiring)
    d) bad secondary windings on the inverter transformer
    e) blown fuse on one of the inverter boards (if multiple boards or multiple fuses)

    4) More details starting with post #19 at

    https://www.badcaps.net/forum/showthread.php?t=10419

    5) Your inverter transformer should measure around 59 ohms according to

    http://www.lcdparts.net/TransformerD...ProductID=3898

    Also, the two heatsinks on the powerboard that are circled in red. They are energized (both when on, and when in standby) with 65v ac. That was a bit of a painful discovery. That cannot be normal right?
    6) Heatsinks are usually live. Usually the power mosfet is attached to it. The board should be clearly marked hot and cold. Treat anything on the hot side with respect and don't touch anything.

    7) My only suggestion for future posts is to have pics more clear and near 2000x2000 resolution, but not any bigger. Otherwise, great first post and great job of getting the repair done on your own this far.
    Last edited by retiredcaps; 05-28-2012, 05:44 PM.
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    Comment

    • tibimakai
      Badcaps Legend
      • Jan 2012
      • 3680
      • USA

      #3
      Re: Vizio vx42l troubleshooting help.

      The Fets show a 8.5K ohm on the inverter boards?

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: Vizio vx42l troubleshooting help.

        When you get part of the screen half lit, that means one of the Inverter board is not working, you have the Master/Slave inverter board setup.
        Please supply good close up pictures of both inverter boards. part number as printed on the board will help also.
        Look real close at the IC on the inverter board and verify the resistance reading of all the MOSFET. The boards may need modification kit
        https://cdn.badcaps-static.com/pdfs/...39dfa5950e.pdf
        OK, I did not see the comment about the burnt pin on the IC, that is very common failure, and if some one replaced the IC and the MOSFETs but did not do the mod, then more likely the problem will happen again.
        LG has issued two mods so far, the first mod did not work, so they issued a second mod (mod II), which I still do not know if that will for sure fix the problem or not.
        Was this TV worked on by some one else before?
        Attached Files
        Last edited by budm; 05-28-2012, 09:07 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

        • noonehere
          New Member
          • Apr 2012
          • 6
          • usa

          #5
          Re: Vizio vx42l troubleshooting help.

          Originally posted by tibimakai
          The Fets show a 8.5K ohm on the inverter boards?
          between 8.4-8.5 yes.

          Originally posted by budm
          When you get part of the screen half lit, that means one of the Inverter board is not working, you have the Master/Slave inverter board setup.
          Please supply good close up pictures of both inverter boards. part number as printed on the board will help also.
          Look real close at the IC on the inverter board and verify the resistance reading of all the MOSFET. The boards may need modification kit
          https://cdn.badcaps-static.com/pdfs/...39dfa5950e.pdf
          All the ccfl's are lighting, but only at the ends, they do not seem to fully ignite. Unfortunantly that's about the limit of my cell camera's detail. Board #'s are PNEL-T707A and PNEL-T708A

          My understanding was the mod was to prevent future driver falure. (mine are not modified) I had seen that, but I did not want to install the mod until I had verified them working in current configuration.


          Originally posted by retiredcaps
          5) Your inverter transformer should measure around 59 ohms according to

          http://www.lcdparts.net/TransformerD...ProductID=3898
          Well I think that may be it. I check the transformers for shorts, and they were all consistent. Unfortunately they were consistently 28 ohms on the secondaries, not 59. So it may be that they are all cooked.

          However my transformers are BJA4B07A23 (A2) rather than the BJA4B07A22 (B) Dunno if that makes a difference. Also, with how badly the work was done on the inverter boards, I would not be amazed that it cooked all four of the transformers.

          Also, thanks for the troubleshooting link! That's a big help.

          Comment

          • retiredcaps
            Badcaps Legend
            • Apr 2010
            • 9271

            #6
            Re: Vizio vx42l troubleshooting help.

            Originally posted by noonehere
            Well I think that may be it. I check the transformers for shorts, and they were all consistent. Unfortunately they were consistently 28 ohms on the secondaries, not 59. So it may be that they are all cooked.
            1) The inverter secondary pins may be in parallel which might cause "invalid" resistance readings (see below). It would be odd for all 4 transformers to be bad.

            My first application of an actual law from

            http://en.wikipedia.org/wiki/Series_...ts#Resistors_2

            56 ohms x 56 ohms / 56 + 56 = 28 ohms.

            2) I see at least one SMD fuse on each inverter board. Make sure both are good. A good fuse should measure less than 1.0 ohms.

            3) It might be worth changing out the caps on the inverter boards (only 4 total). Use something like Panasonic FM or FC.
            --- 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

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