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Vizio VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

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    #1

    Vizio VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

    I have a Vizio VX37L with the typical "LED goes orange to white, no display, will not turn off with power button" failure. BUT. The circuit board is not the one everyone knows and loves(?), it is a different version. The tuner is on the opposite end and there isn't a U33 on the PCB at all.

    The grounding screws are tight, as are the connectors. 12V and 5V are present at the main board and fuses are ok.

    The 1117 I know, but I'm not sure what exactly the other devices with the same package are. Fortunately they all seem to be putting out a voltage matching what it says on their packages.

    The only real odd-balls I find are some high ground levels at the pin 1s of a couple of the 1117s but that might be because they are adjustables at an adjusted voltage? Then why does the other 1117 with similar output voltages have 0V on pin 1?

    Thoughts?






    smaller picture of board so you can see it's different:


    verrrrr big picture of board, so you can make out some details:
    http://d3d71ba2asa5oz.cloudfront.net...ages/vx37l.jpg
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    #2
    Re: Vizio VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

    U5 appears to be defective -- 0.78V between ADJ and OUT, vs typical 1.25V.
    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 VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

      Well I don't have any spare 1117s laying around but . . .





      tom66 thanks for your help!

      Funny what happens when everybody's bandgap references are working. This TV was $$$ and it needed a $0 repair. Thats crazy. No user serviceable components inside . . . or not thanks Jesus!

      Comment

        #4
        Re: Vizio VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

        Nice fix, though I would glue that down for reliability... and you really need to get a proper 1117 as the tab pin is the heatsink and must remain soldered to the board.
        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 VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

          You can buy tiny heatsinks for all the common IC packages, and so long as the heatsink didnt touch any components on the board it would be safe from overheats.
          Fixed so far 12 lcd's , 1 plasmas, 5 monitors, 0 dlp's (plan to keep the dlps at 0). and 3 atx power supplies, and 2 motherboards.

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            #6
            Re: Vizio VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

            Originally posted by cashkennedy View Post
            You can buy tiny heatsinks for all the common IC packages, and so long as the heatsink didnt touch any components on the board it would be safe from overheats.
            Or just solder a small square of a copper sheet on there.
            Muh-soggy-knee

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              #7
              Re: Vizio VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

              That was the proof of concept LOL I didn't leave it like that! While it was dangling at the ends of those wires with the TV working, the regulator barely got warm. The wires are thick enough to conduct "some" heat (they were hard to tin with the small iron) and I cut them to ~1-2cm, just barely long-enough to let me solder them in place.

              The stock part on the stock heat sink was obviously deficient IMO. From my reading of the datasheets, this regulator is rated for free-air operation with no sink for higher current than the old one on a circuit board/heat sink; I'm not worried. If the TV were going on a ship or plane I would have done something more durable, but with the low stress it is likely to encounter, I count the current repair robust enough.

              BUT thanks for all your thoughts/comments!

              Comment

                #8
                Re: Vizio VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

                It's not current but power dissipation that does these devices in. 1A with 0.4V drop is doable with free air. 1A with a 1.7V drop (5V->3.3V for example) isn't. The junction of a semiconductor is always much hotter than the case temperature, which is a poor indicator of device temperature.
                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

                  #9
                  Re: Vizio VX37L Different PCB No Picture, Orange-to-White LED, Will not turn off

                  1A would be pushing it, yes. The AMC1117 is rated for 0.8A (max on a heatsink).

                  Note to others considering this repair: all of the following is somewhat sketchy, and best practice would be a small heat sink on this part, soldered directly to the board. It's my TV though

                  Using 0.8A as a worst-case current an AMC7588 in TO-263 with a 45ºC/W Tja is under Tj=150ºC even over 70º ambient with zero air flow. There is a small but perceptible convection current in there, and I would be astonished if the temperature inside the steel box where this lives ever exceeded 70º When I was using the TV for a little while with the thing bodged on long wires as shown above, it was *barely* warm, like maybe 35º. That, plus knowing these are heavy, short wires going to a small spot of copper on the board, make me entirely satisfied that this should hold up over time.

                  I reserve the right to be mistaken, though. If there is a round two, it will involve a clip-on heat sink.

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