47" Vizio VT470M No picture no sound.

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  • Glitcher
    Badcaps Veteran
    • Mar 2013
    • 673
    • USa
    #1

    47" Vizio VT470M No picture no sound.

    So I got this vizio vt470m. The standby light changes to on however there is no picture. Tried the flashlight test but doesn't seem to be any picture at all. So losing some hope and guessing this might be a bad main board problem here...

    Standby voltage is at a steady 5.25V

    Once I power it on:
    PS_ON goes straight to 4.88V when powered on.

    ON_OFF will increase to 0.11 then goes to 4.8V but it would drop to 0.11 one time but go back to a steady 4.8V and stay there.

    12V pin measures 1.4V
    24V pin measures 0V.

    Checking the Big caps I get 165V on standby and 396V when on.

    Any ideas what the problem will be?
    Tags: None
    • tom66
      EVs Rule
      • Apr 2011
      • 32560
      • UK
      #2
      Re: 47" Vizio VT470M No picture no sound.

      You may have a shorted diode on the 24V line (PSU) or shorted inverter which has not blown the fuse. First try with inverter disconnected to see if 24V line rises.
      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

        • Glitcher
          Badcaps Veteran
          • Mar 2013
          • 673
          • USa
          #3
          Re: 47" Vizio VT470M No picture no sound.

          The fuses on the inverter tested good. but Hmm youre right! with the inverters disconnected the 24V line measures 24.7 and ON_OFF now measures 5.23V
          Last edited by Glitcher; 09-28-2013, 04:34 PM.

            Comment

            • tom66
              EVs Rule
              • Apr 2011
              • 32560
              • UK
              #4
              Re: 47" Vizio VT470M No picture no sound.

              OK, can you post some pictures of the inverter(s)?
              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

                • Glitcher
                  Badcaps Veteran
                  • Mar 2013
                  • 673
                  • USa
                  #5
                  Re: 47" Vizio VT470M No picture no sound.

                  I guess the inverters would be the problem since the 24V line is back when they are disconnected?
                  Attached Files

                    Comment

                    • Glitcher
                      Badcaps Veteran
                      • Mar 2013
                      • 673
                      • USa
                      #6
                      Re: 47" Vizio VT470M No picture no sound.

                      Just tested the mosfets on the both inverters. I removed the two pins off of the pcb and measured them. I found two mosfets on one board to be shorted in all three pins.
                      Last edited by Glitcher; 09-28-2013, 08:48 PM.

                        Comment

                        • Glitcher
                          Badcaps Veteran
                          • Mar 2013
                          • 673
                          • USa
                          #7
                          Re: 47" Vizio VT470M No picture no sound.

                          MOSFETs are labeled:
                          FDB
                          8447L

                          Looks like I found some on digikey!
                          http://www.digikey.com/product-detai...LCT-ND/1626924

                          But meanwhile I found some salvaged mosfets on an old inverter board I had with the same labels. Replaced them to see what'll happen and success! the TV is back to life!
                          Thanks for the help! This TV actually has a really nice picture. I really thought it was going end up as a main board swap.
                          Attached Files
                          Last edited by Glitcher; 09-28-2013, 10:05 PM.

                            Comment

                            • tom66
                              EVs Rule
                              • Apr 2011
                              • 32560
                              • UK
                              #8
                              Re: 47" Vizio VT470M No picture no sound.

                              Nice!
                              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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