Vizio e420i-a0 backlight flashes, then black

[Genaugmen]

When powering on, backlight flashes on (very brief flash, you can just catch the vizio logo center screen), then no backlight. Power light also fades after about 15-20 sec, but I hear that's simply how this model operates normally. Everything remains powered up, and pressing the power button again, power led flashes and the set powers off. When I power up the set I get 129v on both led leads that slowly settle down to a constant 66v. It only hits 129v on that initial flash, and begins dropping immediately. On the connector from the psu to mainboard I get OFF 5.?v on the first two pins (usb), 0v on the others. ON I get 12v on the pins labeled 12v, and around 3.1-3.3 on the the others, USB still 5v. Not sure if there's a screen image. I've tried various lights, but there's so much reflection on that shiny panel, it's difficult to tell. Also checked fuses on mainboard input. OFF 0v, 5,v. ON 11.75v, 5v. I'm leaning towards bad led's, but would appreciate more experienced input.

[budm]

Re: Vizio e420i-a0 backlight flashes, then black

We need good clear well focused pictures of the whole back side of the TV so we can see all the boards and how they are connected together, then good pictures of the top/bottom side of this power supply/LED driver board so we can see board P/N and the labels for each connectors, etc.

[Genaugmen]

Re: Vizio e420i-a0 backlight flashes, then black

Hope they're clear enough.

[Genaugmen]

Re: Vizio e420i-a0 backlight flashes, then black

Forgot this one...

[budm]

Re: Vizio e420i-a0 backlight flashes, then black

The TV has two driver circuits.
This is what you have to do:
Meter in DCV 200V range. LED connector in place.
Leave the black meter probe on the chassis GND.
TV OFF
Put the red probe on LED1+, turn on the TV and note reading to see how high the Voltage goes up to, then wait a few seconds to see if the Voltage will drop down to.
Turn TV OFF.
Move the red probe to LED1-, turn on the TV and note reading to see how high the Voltage goes up to, then wait a few seconds to see if the Voltage will drop down to.
Turn the TV off and do the same for the LED2+, LED2-.

[Genaugmen]

Re: Vizio e420i-a0 backlight flashes, then black

Both led1+ & led2+ 129v-66.1v over roughly 20 seconds.
led1- 86v-26.3v over roughly 20 seconds.
led2- 72v-13.6v over roughly 20 seconds.

[ReeceyBurger123]

Re: Vizio e420i-a0 backlight flashes, then black

You have a failed Led in the screen. Would you like me to link my video on how to test the Leds and repair them ?

[budm]

Re: Vizio e420i-a0 backlight flashes, then black

You LCD panel is LC420DUG as shown in your pictures, according to SJ, it has 10 strips of LEDs, each strip has 5 LEDS, so each string has 25 LEDs.
http://www.shopjimmy.com/lg-lc420dug...ps-1-board.htm
Vf for 25 LEDs is series should be about 25 x 3V = 75 V
Per your readings:
Total VF of LED string 1 = 129V - 86V = 43V.
Total VF of LED string 2 = 129V - 72V = 57V.

It looks to me some of the LEDs are shorted out, the LEDs will still light up but the over current protection will kick in and shutdown the LED boostconverter power supply.
Pictures provided by shojimmy.

[Genaugmen]

Re: Vizio e420i-a0 backlight flashes, then black

So I guess my fix is to replace with a new set of leds?! I've seen guides on testing individual led, and I've replaced them in a set before. Just wanted some confirmation on my own assessment sounding correct. As far as the led strips I can't find them for the e420i, but I see plenty for the e420(without the "i"). I'm assuming that they're most likely the same. They look exactly the same. $16-$20 per single strip.

[budm]

Re: Vizio e420i-a0 backlight flashes, then black

The main key is to match the LCD panel with the LED strip.

[budm]

Re: Vizio e420i-a0 backlight flashes, then black

https://www.badcaps.net/forum/attach...7&d=1463682166

LC420DUG JFR1.
Contact SJ.

[Genaugmen]

Re: Vizio e420i-a0 backlight flashes, then black

I see. Every strip isn't identical. I won't be able to get into that until later tonight. Thanks for the help!

[ReeceyBurger123]

Re: Vizio e420i-a0 backlight flashes, then black

Please take the time to watch this, will save alot of time and money than faffing about replacing all the strips:

https://m.youtube.com/watch?v=RxwdC7V5Ue0

[SLK001]

Re: Vizio e420i-a0 backlight flashes, then black

I'm currently working on a Vizio E470i-A0 smart TV with two LEDs out. Symptoms were identical to yours.

I just replaced the LEDs and verified all the strips are working. I am currently waiting for the epoxy that I used to replace the lenses to setup.

You can replace all the strips for ~$50, or fix the bad ones for ~$5-10. Your choice - depends on your skill level.

[budm]

Re: Vizio e420i-a0 backlight flashes, then black

I see. Every strip isn't identical. I won't be able to get into that until later tonight. Thanks for the help!

Once you are done fixing, make sure to turn down the backlights level to as low as possible to extend the life of the LEDs.

[Genaugmen]

Re: Vizio e420i-a0 backlight flashes, then black

I'm currently working on a Vizio E470i-A0 smart TV with two LEDs out. Symptoms were identical to yours.

I just replaced the LEDs and verified all the strips are working. I am currently waiting for the epoxy that I used to replace the lenses to setup.

You can replace all the strips for ~$50, or fix the bad ones for ~$5-10. Your choice - depends on your skill level.

What's your source for $5-10/each? I found some new for $20 each.

[ReeceyBurger123]

Re: Vizio e420i-a0 backlight flashes, then black

What's your source for $5-10/each? I found some new for $20 each.

Watched my video ?

[SLK001]

Re: Vizio e420i-a0 backlight flashes, then black

What's your source for $5-10/each? I found some new for $20 each.

I'm not talking LED strips. I'm talking repairing the strips you have with replacement LEDs (for the bad LEDs). I've got some extra LG LM100s, if these are the type for your strip.

[Francorea65]

Re: Vizio e420i-a0 backlight flashes, then black

I have problems with a Vizio E420i-A0 television, it turns on normally, gives image and sound, after 5 minutes the image fades and there is a black screen, I have audio. I did a flex test on the panel card, on the left side it presents me with the problem and on the right side the image works correctly