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Vizio 42" LED TV No backlight, blows fuse

Discussion in 'Electronic Repair' started by Sparkey, Mar 5, 2013.

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  1. Sparkey

    Sparkey Guest

    Hi;

    This is a Vizio M420NV.
    Backlight was out, I found an open 3A fuse (TF1) on the main board that carries 12.4 vdc. When fuse replaced, the backlight will flash a couple of times and poof goes the fuse again.

    I don't have a diagram. I wonder if this might be due to a inverter fault ?
    I checked power transistors on main and power supply board.
    Any ideas ?

    Thanks,
     
  2. N_Cook

    N_Cook Guest

    carries 12.4 vdc. When fuse replaced, the backlight will flash a couple of
    times and poof goes the fuse again.

    Can you hear any fizzing/arcing across turns in the inverter Tx ?
    Can you reduce the mains voltage a bit and maybe increase the amount of
    on-time a bit , to monitor the fault situation a bit longer.
     
  3. John-Del

    John-Del Guest

    The fuse for the 12V feed to the main does not cover the inverter B+, that's fed directly from the smps to the inverter board(s) and fused at that end.. The inverter was blinking because the main is gimpy..

    If the 12V fuse on the main is opening, you most likely have a shorted regulator IC on the main, and possibly an IC after that drawing and overheatingthe regulator. Unfortunately, Vizio is loathe to provide any service information on their boards. You're best bet at this point is to replace the main. Make sure you get the correct one as there are typically several versions for the same model to match the display\tcon.
     
  4. Sparkey

    Sparkey Guest

    The fuse for the 12V feed to the main does not cover the inverter B+,<<

    Ahhh, that's what I wanted to know...

    I needed to confirm that the inverter was not powered from main board.
    So my problem is likely localized to the main board.
    I will have another look at the power transistors and IC's tomorrow.

    Thank you !!
     
  5. Sparkey

    Sparkey Guest

    Tomorrow I will try to dial down the power a bit and see if the invert xformers fizzle with a new fuse...

    Thanks
     
  6. Guest

    Hi there, I would also check any electrolytic capacitors on the inverter board, making sure they are at least 105 degree celcius type with low equivalent series resistance - low ESR type.
     
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