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    ViewSonic VA712b goes black after power on

    Hi Forumers

    I have a ViewSonic VA712B Monitor that it powers but as soon as it receives a signal the led goes green but i only see a flicker and goes black. By turning it off and on it works but with whine sound that its been like that for a year now. If I turn off the monitor the whine still there. Got a new monitor, but want to fix this one for my kid new old computer.

    What i have done so far - Open the back case to find very little regular capacitors, most are surface mounted and the PCB looks very clean for the age this have. Check connections and solder joints

    I posted a video of the whine it makes just hope YouTube don't mess with the already crappy audio. VA712 Inverter

    Btw I cannot find anything related to the inverter transformers they have a number SIT36350-1736 G534T
    Attached Files
    A Picture of subject is always Welcome


    Things saved from the e-landfill:
    Vizio VA26LHDTV10T 26" - Bad EEPROM Cap
    Asus PTGD1-LA Full Recap - Cha1 DDR socket damage
    MSI PM8M3-V Unstable CPU Recap CPU VRM circuit
    ViewSonic VA712B - still working on it
    Kindle Fire USB Connector
    MSI G31M-F Full Recap - Record Breaker done in 3Hrs.
    MSI P67A-G43 BIOS chip Reprogram - Tested and Happy

    The list will go on thanks to the people of this forum and many hours of reading.

    #2
    Re: ViewSonic VA712b goes black after power on

    Can I see the straight shot pictures of the whole board and also the inverter transformer?
    I can see the number on one of the MOSFET (4410, N-CHANNEL)) that drives the inverter transformer, another one is FDS4435. Check the resistance between D and S, D and G, S and G.
    Check the resistance of the transformer between 2 and 1, 2 and 3.
    Attached Files
    Last edited by budm; 08-15-2013, 08:54 AM.
    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


      #3
      Re: ViewSonic VA712b goes black after power on

      Whole Inverter Power Board and The whole assembly ( logic and power inverter board).

      To take reading do I remove the transformer and MOSFET. Read about that somewhere here on the forum but don't recall.
      Attached Files
      Last edited by crash-cyberdrive; 08-15-2013, 11:05 AM. Reason: Added Picture
      A Picture of subject is always Welcome


      Things saved from the e-landfill:
      Vizio VA26LHDTV10T 26" - Bad EEPROM Cap
      Asus PTGD1-LA Full Recap - Cha1 DDR socket damage
      MSI PM8M3-V Unstable CPU Recap CPU VRM circuit
      ViewSonic VA712B - still working on it
      Kindle Fire USB Connector
      MSI G31M-F Full Recap - Record Breaker done in 3Hrs.
      MSI P67A-G43 BIOS chip Reprogram - Tested and Happy

      The list will go on thanks to the people of this forum and many hours of reading.

      Comment


        #4
        Re: ViewSonic VA712b goes black after power on

        You can measure the resistance with parts still in place, we are looking for really low Ohms reading on the MOSFET if they are bad, then we will remove it to verify that part off the board again. The transformer reading should be within 3% from each other.
        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


          #5
          Re: ViewSonic VA712b goes black after power on

          Hi Budm
          Finally got the readings of the components.
          Readings on
          T1: 2-1= OL 2-3=1.55kΩ
          T2: 2-1= OL 2-3=1.577kΩ
          T3: 2-1= OL 2-3=1.564kΩ
          T4: 2-1= OL 2-3=1.581KΩ
          I think not too large a difference.

          FDS4435-1 MOSFET
          D-S=489Ω
          D-G=1.46kΩ
          S-G=742Ω

          FDS4435-2 MOSFET
          D-S=487Ω
          D-G=1.43kΩ
          S-G=722Ω

          SI4410-1 MOSFET
          D-S=466Ω
          D-G=OL
          S-G=610Ω

          SI4410-2 MOSFET
          D-S=488Ω
          D-G=OL
          S-G=605Ω
          Attached Files
          A Picture of subject is always Welcome


          Things saved from the e-landfill:
          Vizio VA26LHDTV10T 26" - Bad EEPROM Cap
          Asus PTGD1-LA Full Recap - Cha1 DDR socket damage
          MSI PM8M3-V Unstable CPU Recap CPU VRM circuit
          ViewSonic VA712B - still working on it
          Kindle Fire USB Connector
          MSI G31M-F Full Recap - Record Breaker done in 3Hrs.
          MSI P67A-G43 BIOS chip Reprogram - Tested and Happy

          The list will go on thanks to the people of this forum and many hours of reading.

          Comment


            #6
            Re: ViewSonic VA712b goes black after power on

            Had to take new readings of the components, the mosfet's were tested wrong. Im a newbe on testing mosfet components.
            Readings on Transformers stayed the same
            T1: 2-1= OL 2-3=1.55kΩ
            T2: 2-1= OL 2-3=1.577kΩ
            T3: 2-1= OL 2-3=1.564kΩ
            T4: 2-1= OL 2-3=1.581KΩ
            I think not too large a difference.

            FDS4435-1 MOSFET Specified Value on Datasheet –8.8 A, –30 V RDS(ON) = 20 mΩ @ Vgs = –10 V
            D-S=651Ω
            D-G=1725Ω
            S-G=930Ω

            FDS4435-2 MOSFET
            D-S=651Ω
            D-G=1713kΩ
            S-G=935Ω

            SI4410-1 MOSFET Specified Value on Datasheet Rds(on)Ω 0.0135 @ Vgs = 10V My DMM uses a 9V battery so it should be close.
            D-S=612Ω
            D-G=OL
            S-G=793Ω

            SI4410-2 MOSFET
            D-S=614Ω
            D-G=OL
            S-G=804Ω

            I dont know much about Mofset but aren't those readings a bit too high?
            Last edited by crash-cyberdrive; 08-18-2013, 08:07 AM. Reason: Added MOSFET Information fron datasheets
            A Picture of subject is always Welcome


            Things saved from the e-landfill:
            Vizio VA26LHDTV10T 26" - Bad EEPROM Cap
            Asus PTGD1-LA Full Recap - Cha1 DDR socket damage
            MSI PM8M3-V Unstable CPU Recap CPU VRM circuit
            ViewSonic VA712B - still working on it
            Kindle Fire USB Connector
            MSI G31M-F Full Recap - Record Breaker done in 3Hrs.
            MSI P67A-G43 BIOS chip Reprogram - Tested and Happy

            The list will go on thanks to the people of this forum and many hours of reading.

            Comment

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