Vizio SV470XVT1A LCD, amber logo but unresponsive

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  • Curious.George
    Badcaps Legend
    • Nov 2011
    • 2305
    • Unknown

    #1

    Vizio SV470XVT1A LCD, amber logo but unresponsive

    Cleaning out the shed. Old Vizio SV470XVT1A shows orange standby logo. And no other signs of life.

    (measurements with DSO doing the math for me)

    No toasted components, no visibly bad caps, etc. hence no attached photos (see below)

    +5VSB at 5.14 "DC"
    +3.3VSB at 3.32 "DC" (sourced by U22)

    All other regulators downstream of the switched (U14) +5VSB are out of wack.

    U14 is 49536M (dual 30V, 5A, P-channel) wired in parallel as a single switch.

    U14 source is +5VSB. Drain shows ~3.2V, with a 300mV, ~25Hz square wave riding atop it. Gate mimics drain. U14 is warm suggesting it's actually passing current with an IR drop across it (recall, source is 5.14V).

    Gate should be ~0V -- Vce(sat) of Q2 driving it behind a ~100K R7.

    Bad FET? Or, is R7 actually open and the 100K a misread of other impedances in the circuit? (I'd have expected R7 to be closer to 10K)

    [I'll tear open another Vizio and see what the equivalent circuit topology is, there, and possibly get a better feel for what "R7" should be]

    Does this look like a typical failure mode? I'll look for a U14 cross and replace the thing as that seems a straightforward course of action.

    (sigh) I think any future TV purchases will be conditional on manufacturers having schematics available -- even if hard to find!

    Thanks!

    (Please reply to forum as my PM is munged)
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: Vizio SV470XVT1A LCD, amber logo but unresponsive

    Please up load good clear pictures of the whole back side of the TV showing all the boards.
    What DCV do you have on the connector of the power supply board that goes to the main board? We need to see if it has any command signals form the main board or not.
    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

    • Curious.George
      Badcaps Legend
      • Nov 2011
      • 2305
      • Unknown

      #3
      Re: Vizio SV470XVT1A LCD, amber logo but unresponsive

      Originally posted by budm
      Please up load good clear pictures of the whole back side of the TV showing all the boards.
      What DCV do you have on the connector of the power supply board that goes to the main board? We need to see if it has any command signals form the main board or not.
      Sorry for the misunderstanding. I'm not looking for help in diagnosing the problem. Rather, I provided a quick summary of the symptoms that would be evident and wondering if they were common enough to merit my spending time more fully documenting process, observations (scope traces), reasoning, etc. BEFORE closing up the set.

      I.e., if it was a common set of conditions (beyond "main board appears bad"), to provide guidance as to what to look for and how to come to a successful diagnosis.

      [Ship has sailed; I already buttoned up the set as my SO was complaining about the space it took up on the living room floor ]

      Comment

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