VIZIO E420i LED Strip Issue

[Michale32086]

I have a Vizio E420i with an apparent backlight strip issue.. I say "apparent" because I'll be damned if I can figure out what the problem is.

I know I am using a good Main Video Board and a good Power PCB...

I can only get the three middle LED strips to light up..

I know all the strips are good for three reasons..

1.I have tested them with my LED Power Strip tester and they all check out...

2.I have swapped them around and put them all in the middle 3 at one time or another and they all work..

3.I use my LED tester and put the probes on the pins as noted in the pic and the outer ones come on...

But I can't get them to work normally...

This is a real stumper for me. Anyone have an idea???

[budm]

Re: VIZIO E420i LED Strip Issue

Can we see straight shot pictures of the power supply board with LED connector in place?
You have two set of LED strings, One set has three subset of the LED strips all connected in series, the second set has two strips (the two that are not lit up) of the LED connected in series.
The SMD connectors that used for linking the strips are known for bad connections.

[budm]

Re: VIZIO E420i LED Strip Issue

https://www.badcaps.net/forum/attach...6&d=1510944751
Also need the whole picture of this board.

[Michale32086]

Re: VIZIO E420i LED Strip Issue

Thanx for the reply BudM...

Pics attached..

[budm]

Re: VIZIO E420i LED Strip Issue

So yes, you do have two set of the LED strings so two driver circuits, one set has 3 strips, another set has two strips.
So you need to test each pair of the LED wires (White/Yellow). Do each pair light up with the tester?

[Michale32086]

Re: VIZIO E420i LED Strip Issue

Yes...

When I use the LED tester on #1, the outer LED strips (2) light up..

When I use the LED tester on #2, the inner LED strips (3) light up..

[budm]

Re: VIZIO E420i LED Strip Issue

OK, then you need to check the DCV on all 4 wires at the LED connector with the connector in place. You will leave the TV off, Black probe on the chassis, red probe on one of the four wire then turn on the TV and look at the meter, then wait 10 seconds and record the reading, turn off the TV and move the red probe to the other wires and repeat the test, so 4 test total.
LED1 -
LED1 +
LED2 -
LED2 +

[Michale32086]

Re: VIZIO E420i LED Strip Issue

OK, I am on it.. Give me a few...

[budm]

Re: VIZIO E420i LED Strip Issue

I like to see the pictures of the bottom side of the board too.

[Michale32086]

Re: VIZIO E420i LED Strip Issue

OK It was kinda weird..

1- 5v

2- 0v

3- Started out at 0V, then as the LEDs did their DIM and BRIGHT thing, the voltage shot up to around 75V then down to 12V and pretty much held steady..

4-115V

[budm]

Re: VIZIO E420i LED Strip Issue

OK It was kinda weird..

1- 5v

2- 0v

3- Started out at 0V, then as the LEDs did their DIM and BRIGHT thing, the voltage shot up to around 75V then down to 12V and pretty much held steady..

4-115V

The LED1+ and the LED2+ are the Voltage feeding pin to the Anode of each LED string, so one of the boost converter is not working.
LED1- AND LED2 - are the Cathode return for each set of the LED strings.

[budm]

Re: VIZIO E420i LED Strip Issue

https://www.badcaps.net/forum/attach...5&d=1510950536
I can see one of the two boost converter section has over heated, you can see the board turns brown color by the SMD MOSFET.

[Michale32086]

Re: VIZIO E420i LED Strip Issue

That's so weird because the Power PCB works fine in another identical E420i...

I have tried 4 different Power PCB boards that all work fine in one E420i, but won't work in this one..

Bizarre....

[budm]

Re: VIZIO E420i LED Strip Issue

Then are you sure that the Voltage readings on the LED connector are correct because if the power supply board is good then you should at least see the Voltage at PIN 2 LED1 + and PIN 4 LED 2+, Right now you are gettinG nothing on PIN 2 LED1+.
Disconnect the LED connector and recheck LED1 + and LED 2+ on the board again.
The pin numbers are the number as printed on the power supply board.

[Michale32086]

Re: VIZIO E420i LED Strip Issue

The ONLY board I haven't swapped out is this board:

https://www.badcaps.net/forum/attach...8&d=1510946436

Could that be the culprit??

[budm]

Re: VIZIO E420i LED Strip Issue

BTW, you should check the Voltages right at the power supply board LED connector to be sure, you may have open connection from the power supply board to the board on the LCD panel.
It sounds like you have open connection.
https://www.badcaps.net/forum/attach...9&d=1510946436

[Michale32086]

Re: VIZIO E420i LED Strip Issue

Then are you sure that the Voltage readings on the LED connector are correct because if the power supply board is good then you should at least see the Voltage at PIN 2 LED1 + and PIN 4 LED 2+, Right now you are gettinG nothing on PIN 2 LED1+.
Disconnect the LED connector and recheck LED1 + and LED 2+ on the board again.
The pin numbers are the number as printed on the power supply board.

OK I'll disconnect the connector from the LED strip and check it from the board connector..

[Michale32086]

Re: VIZIO E420i LED Strip Issue

Same voltages...

I'll have to pick this up in the morning.. Gotta head home..

Thanx for the assist, BudM...

[budm]

Re: VIZIO E420i LED Strip Issue

Well that means one of the LED boost Voltage is not present on that power supply board.
Are you sure that ALL the LED strings light up using this same exact board in the same TV model with LCD panel that has two set of LED strings?
There must be an error some where.

[SLK001]

Re: VIZIO E420i LED Strip Issue

Look for broken connections on all the connectors for each strip that doesn't light.

Have you tried to swap strips (one that lights for one that doesn't)? You might be able to zero in on a possible bad connection/strip. The circuit for these backlights actually goes from one to another - one break in a connection will kill the whole circuit.