Vizio E55-D0 Picture Flashes

[Tech 57]

This TV has the video flashing
When no signal is there or hdmi is connected it flashes
if i remove the attenna it says no signal backight is steady so i dont think the backight strips are bad.sounds like a main board.
What's your Opinion Thanks phil

[R_J]

Re: Vizio E55-D0 Picture Flashes

When there is no signal the backlights are usually lowered, so it still could be a backlight issue, Go into the menu and lower the backlight adjustment and see if the flashing changes.

[Tech 57]

Re: Vizio E55-D0 Picture Flashes

So you think bad led strips?
I guess i should strip the panel down
Thanks

[Andrew F. Ali]

Re: Vizio E55-D0 Picture Flashes

Is everything else working?? This points to a backlights issue. and RJ is correct. Probably try turning the Backlight Level down (not the Brightness or Contrast Levels) to about 55%. That may give you a temporary fix.

[Tech 57]

Re: Vizio E55-D0 Picture Flashes

ok i did lower the backlights setting to dark in the menu setting it stopped so that means backlight strips are bad?

[Andrew F. Ali]

Re: Vizio E55-D0 Picture Flashes

That's a roger!!!!

[caphair]

Re: Vizio E55-D0 Picture Flashes

I have this same issue. On the led driver board there are test points for each led strip.
LED 10 measures 0v
LED 6 - 9.2v
LED 5 - 9.2v

All other strings have 12.5v sometimes measured 14v
45v at the Vout test pins

So I’m guessing the LED 10 strip has failed completely? But I’m wondering why 5 and 6 have lower voltages compared to the others. Separate issues on their way out?

[budm]

Re: Vizio E55-D0 Picture Flashes

You have ten LED strings so it has 10 MOSFET'S on the LED driver board for the Cathode return for each LED string, the Cathode of each LED string is connected to the Drain pin of each MOSFET so if the string has open circuit then you will not have Voltage on the drain pin.
Looking at your cutoff picture I cannot read or tell what the pin names are, too small for my eyes to see.

[caphair]

Re: Vizio E55-D0 Picture Flashes

You have ten LED strings so it has 10 MOSFET'S on the LED driver board for the Cathode return for each LED string, the Cathode of each LED string is connected to the Drain pin of each MOSFET so if the string has open circuit then you will not have Voltage on the drain pin.
Looking at your cutoff picture I cannot read or tell what the pin names are, too small for my eyes to see.

So each string is being independently driven as oppose to having one huge voltage put through all strings tied in series like other TVs?

What's the 45v out then? There's 4 pins total labeled Vout, 2 pins on 2 connectors where the led strings are split up

[budm]

Re: Vizio E55-D0 Picture Flashes

The 45V is for feeding the Anode of each LED string , the Cathode return of each string is connected to the PWM controlled MOSFET DARIN for maintaining the constant current through each LED string, the source is connected to the current sensing resistor, the other end of the resistor is connected to circuit GND.
Your TV has local dimming backlights that adjust itself based on video content.

[caphair]

Re: Vizio E55-D0 Picture Flashes

The 45V is for feeding the Anode of each LED string , the Cathode return of each string is connected to the PWM controlled MOSFET DARIN for maintaining the constant current through each LED string, the source is connected to the current sensing resistor, the other end of the resistor is connected to circuit GND.
Your TV has local dimming backlights that adjust itself based on video content.

Ah ok. Didn't know it had local dimming. Looking at it for a friend. Is that why the backlights flash when powered on because one string is open?

Are the other two strings measuring lower voltage due to dimming or an imminent failure of the strings? Btw no source connected to the tv so just a “no signal” when on

[budm]

Re: Vizio E55-D0 Picture Flashes

The string that has open circuit will show 0V on the Drain pin of he MOSFET on that LED driver board, so how may of them show 0 V on the Drain pin?
The protection circuit probably kicks in die to no current flow detected.
This is where LED tester comes in handy when you have to test 10 LED strings.

[caphair]

Re: Vizio E55-D0 Picture Flashes

The string that has open circuit will show 0V on the Drain pin of he MOSFET on that LED driver board, so how may of them show 0 V on the Drain pin?
The protection circuit probably kicks in die to no current flow detected.
This is where LED tester comes in handy when you have to test 10 LED strings.

Only the LED 10 shows 0v. Led 5 and 6 show 9v and the rest are 12v. The led driver board has two test points for each led string labeled.

[budm]

Re: Vizio E55-D0 Picture Flashes

If that is the case then it looks like it has open circuit.
There are more than one model of LCD panel used in this TV.
https://www.shopjimmy.com/catalogsea...q=Vizio+E55-D0

[caphair]

Re: Vizio E55-D0 Picture Flashes

If that is the case then it looks like it has open circuit.
There are more than one model of LCD panel used in this TV.
https://www.shopjimmy.com/catalogsea...q=Vizio+E55-D0

Would that one open circuit cause low voltage on the other two led strings?

[budm]

Re: Vizio E55-D0 Picture Flashes

You have 10 separate control circuits for 10 LED string.
The lower the Voltage on the return pin the more current through the LED string that is because the on time of the MOSFET will on longer so the Vdrops between Source and Drain will be less.
You can find out if LED 10 string has open circuit or not by swapping LED 10 return wire with other LED return wire and see if the 0V reading will follow or not, or you can have just one LED string connected one a t time and see if each one of them will come on or not, or you can use power supply (set current limit to about 50mA ~ 100mA) that ha high enough Voltage to drive the LED string and test each string.