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Vizio L30WGU, powers up for a few seconds then returns to standby.

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    #1

    Vizio L30WGU, powers up for a few seconds then returns to standby.

    I found this TV last week and haven't put much effort into it. It's kind of a lazy Saturday morning here so I decided to pull it out and have a look at it. There was an obviously bulged cap on the PSU. I swapped it out but still have the same issue. In standby, at the PSU, I have

    12V = 12V
    12V = 12v
    12v = 12v
    GND = 0v
    GND = 0v
    GND = 0v
    D = 0V
    C = 1.5V

    At power up, the LED turns from amber to green, the backlights flash briefly (maybe a half second) and I see the following voltages

    12V = 12V
    12V = 12v
    12v = 12v
    GND = 0v
    GND = 0v
    GND = 0v
    D = 3.5V
    C = 1.5V

    These voltages hold steady for ~3sec and then the 3.5V drops back out at which point the green LED reverts back to amber. On the main board, I have 3 fuses, they read

    F1 = 12V steady on both sides
    F3 = 5V steady on both sides
    F2 = 3.3V steady on both sides

    These voltages do not drop out when the PSU shuts off. I see one voltage regulator with a shape that I'm familiar with.

    U20
    38AU
    N12A
    3.3V
    1.8V
    0.1V

    These voltages don't change at power up or standby.

    I'm leaning towards a main board issue. I'm hoping this can be fixed at a component level. The only main boards that I can find for this set are ~$80 which is more than I really want to put into a 9 year old TV. If I can get this thing to just show a picture, I will be happy. My plan is to give it to my brother to use as a computer monitor.
    Attached Files
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    #2
    Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

    OK you see those coils on the main board, left hand side? On the end not connected to the diode, you should see a steady DC voltage.
    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

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      #3
      Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

      The top coil shows 5v at the point shown in the pic. The other coil shows 3.3v.
      Attached Files

      Comment

        #4
        Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

        Perhaps try forcing the backlight on to see what you get. If you see graphical noise or corruption I'd suspect the video processor (PixelWorks IC.)
        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

        Comment

          #5
          Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

          I can't get it to stay on. With the main unplugged, applying 3.5v to or grounding that D pin only gives a very brief flash when the voltage or ground is pulled off.

          Comment

            #6
            Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

            I'd suggest you test if those crystals (oscillators) are all working.

            Other than that, I have no immediate suggestions. If schematics were available I could help more but I guess they aren't.
            Last edited by tom66; 01-26-2013, 12:37 PM.
            Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
            For service manual, schematic, boardview (board view), datasheet, cad - use our search.

            Comment

              #7
              Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

              1) If you hookup a DVD player so you get a picture and sound, do they both stay on?

              2) On the inverter board, it looks like some Darfon branded inverter transformers?

              You can measure the secondary resistances and report them like so

              https://www.badcaps.net/forum/showpo...6&postcount=20

              3) U23 and U25 on the main board are also regulators

              https://cdn.badcaps-static.com/pdfs/...cd58db5a46.pdf
              Last edited by retiredcaps; 01-26-2013, 03:14 PM.
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                #8
                Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

                4) I found a couple of more regulators. I can't be sure since I can't read the part numbers. All circled in red.
                Attached Files
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                  #9
                  Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

                  From retiredcaps pic...

                  Upper left regulator
                  U23
                  XM46AQ
                  LM2596S
                  -5.0 P+
                  12.16V
                  4.95V
                  0V
                  5.05V
                  0V
                  From bottom to top, voltages are steady when in standby or powered on

                  Next one below that...
                  U25
                  JM44AQ
                  LM2596S
                  -3.3 P+
                  12.15V
                  3.07V
                  0V
                  3.31V
                  0V
                  From bottom to top, voltages are steady when in standby or powered on

                  The next one is U20 that I reported on earlier, the bottom regulator furthest to the left in retiredcaps pic.

                  The next one is all the way to the top, right above the heatsink.
                  QT1
                  C5886
                  3.65V
                  12.13V
                  3.3V
                  From bottom to top, voltages are brief when powered on. All read 0V in standby.

                  Last one...
                  UT4
                  KA7809
                  12.13V
                  0V
                  9.04V
                  From left to right, voltages are brief when powered on. All read 0V in standby.
                  Attached Files

                  Comment

                    #10
                    Re: Vizio L30WGU, powers up for a few seconds then returns to standby.

                    Those first two are switching converters, not regulators.
                    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                    Comment

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