Vizio D55x-g1 (55" 4K, no backlight, has Audio and picture)

[WayOfTheRoad]

Hello, everyone. A neighbor was throwing this TV away for "not turning on" so I asked for it and they gave it to me for free since Vizio gave them a new TV under warranty.

I'm pretty proficient with electronics in general but this is the first TV I've ever tried to fix. I strongly suspect bad LED lights but figured I'd post some info and see if those of you more experienced with TVs can confirm my suspicion before I move forward. Some photos and measurements below:

The power supply only has two outputs, one output cable going to the main board and the other output cable leading into the chassis to the LCDs.

The voltages on the pins/cable going to the main board are such (first when in standby, then powered on):

On/Off - 10mv , 3.3v
NC - 52mv , 3.3v
GND - 0 ,0
GND - 0, 0
VA - 15v, 18v
VM - 15v ,18v
VM - 15v , 18v
NC - 15v, 18v

DIM - 104mv , 3.3v
PS_ON - 52mv , 3.3v
GND - 0, 0
GND - 0, 0
VA - 15v, 18v
VM - 15v , 18v
VM - 15v, 18v
NC - 15v , 18v


So, those all seem good to me based on the limited knowledge I have about TV power supplies. The only strange thing I notice is the AC input voltage is 60v up to the large Bridge Rectifier spitting out 170dcv. I've seen this before but didn't know TVs dropped the 120v here to 60v.

The measurements of the LED cable/pins is such:

All LED+ show 21v on standby and upon powering up jumps to 51v before falling back down to a stable 25.5v.

All LED- show 240mv on standby and jump to 20v and then 30v for a second before falling back down to a stable .988v


As for the TV functionality, it has a picture that can be seen with a flashlight and it has audio. It seems like an LED problem but I'd hate to order anything without having someone more experienced with TVs confirm this. The only oddity I found was in the A/V input it had crackling audio but it could be due to plugging the TV and AV device into the same power strip. The audio was fine on all other inputs.

Thanks for any help! The TV was free so I'm not out anything until I buy replacements. I plan to keep it if it gets fixed so I'm also up for experimenting if any of you think it may be something else other than LEDs. Thanks!

[dskall]

Re: Vizio D55x-g1 (55" 4K, no backlight, has Audio and picture)

If you unplug t-con and power on do backlights, come on?

[WayOfTheRoad]

Re: Vizio D55x-g1 (55" 4K, no backlight, has Audio and picture)

If you unplug t-con and power on do backlights, come on?

Hello and thanks for the reply.

No, they do not come on if I do that.

[WayOfTheRoad]

Re: Vizio D55x-g1 (55" 4K, no backlight, has Audio and picture)

Hate to double post (I don't see an edit function via mobile) but a bit more info below. First I'll add a quick TL;DR and then full detils with extra photos:

TLDR:
The LEDs seem to work upon all tests I know how to do. All six strips light up if given 26v from my bench PSU and all individual LEDs test good with a multimeter. Given that there is no LED logic past the cable coming from the Power Board, I assume it means the LEDs are actually good. Then again, I've come across some weird stuff regarding LED strips in my time so...?
Some weird findings here and there but overall good.




FULL DETAILS:

I took it apart down to the LEDs and things are...strange. At least for a TV beginner like me as this seems more diabolical than anything I've encountered in GPUs, consoles, laptops, etc.

So, I fully expected the LED strips to be bad (at least one or some individual LEDs). It's 39 total LEDs that are in six total strips, arranged in three rows. So each row has two strips that are connected at the middle with a basic lock connector. The strips each have the +/- test pads at the front of the strip, as well as pads between each LED to test individually. Further, there is no extra board or logic between the power supply and LED strips. The cable goes from the PSU to the 3 rows of strips directly. So, clearly, the PSU or Main Board is also acting like the LED driver.

I first tested by leaving the strips as installed from factory (arranged in 3 rows, 2 strips connected per row) and used my power supply to put 26v at the test points nearest the power input cable.
The first strip in the first row lights up fully. I find it odd that the entire row doesn't light up (even dimly) but I then test the second strip in the row and it also lights up entirely. Each strip is pulling about 18-20v on their own. Nice and bright. Amperage is about .125-250ma, IIRC.

This ends up being true for all of the 6 LED strips. Yet, when connected they don't all light up and this seems insane to me so I check the resistance on the middle connectors that connect them. I merely check + to + , - to - across the connector and...

...most have insanely high resistance. The lowest any of them had was the + to + on the 2nd row of strips and that was 20ohm. Not bad but not good. The worst of them was 478ohm! Again, this is just testing the direct connection across the connectors, not fully end to end.
So, I think this may be the issue and I add a bit of solder to the metal pin in each male connector. I snap them back together and now all have a direct connection. It reads 0.4ohm across all (the resistance of my leads) so it's now strongly connected for each.

I then test the strips again and got the same result, lol. They will light fully by themselves connected or disconnected from each other but no row will fully light up when power is applied to the test pads nearest the main power input.

So I test each LED by itself. Maybe one or a few LEDs are bad and they lit due to...me brute forcing 26v into the strips?! Something? Worth a look.
I test them individually in diode mode and all test fine. All 39 LEDs across the 6 strips. All test fine. They all light from my multimeter (however dimly) and show no shorts. All identical readings both ways. Voltage goes one way, not the other...like a diode lol.

So I go back to suspecting the Power Board. As noted above, it gives 21v in standby and 26v while powered on. If true and one strip lights up at about 18-20v in the testing mentioned above, a single strip should light up if connected to the power supply even in standby, right?

No. Nothing. I even forced the PSU on by shorting the PS_ON pin and even then nothing happens.

So I then suspected the cable running from PSU to LEDs itself and it tests fine. Good continuity from input to output.

I'm back to having no idea what's wrong. Are LED strips so weird that they could light on their own and show no shorts but still be bad? Can a PSU deliver the voltage supposedly needed and still not light good strips?
I'm back to having no idea what's wrong. I feel like I did when I began learning about electronics as a child, lol.

Thanks for any insights.

[nomoresonys]

Re: Vizio D55x-g1 (55" 4K, no backlight, has Audio and picture)

wonder if it's the same issue Yanleb had here: https://www.badcaps.net/forum/showthread.php?t=104720

[WayOfTheRoad]

Re: Vizio D55x-g1 (55" 4K, no backlight, has Audio and picture)

wonder if it's the same issue Yanleb had here: https://www.badcaps.net/forum/showthread.php?t=104720

Thank you for the reply! I do have a new update and it's not far off from the issue you linked.
In my case, I just had to clean-up the bit of solder I added in the 2nd row strip. I had inadvertently created a small bridge in the back of the prongs that I missed due to the tiny size of the connector.

So I got the lights up and running, reassembled and...

...womp womp womp. Screen is boned. I was super, super careful. I used suction cups and made sure not to bend any part beyond a few degrees. Yet, the edges are messed up and don't refresh properly. It also now has a horizontal line across the screen

Now, it's possible that it was always bad as the part I could see with the flashlight pre-repair is a part of the screen that is unaffected. So I could see picture and also know that it wasn't cracked. It remains uncracked but it isn't good. It may have been damaged during removal because as careful as I am, I also don't like to pretend I can't make a mistake. It could have been my doing, maybe not. I'm 50/50 as of this moment. Maybe the neighborhood damaged it taking it to the curb?
I'll try to post a more photo or video later.

So, the lesson to anyone seeing this is to make sure the connectors in your LEDs are making good contact! From the factory these had AWFUL connections and that was all that was wrong with this set (if I damaged the panel). Something as dumb as cheap/bad connectors might have made my neighbor toss it away and Vizio sent him a check for warranty.