Vizio M70-C3 Dark Spots

[kentkirchner]

Hello, brand new to the site and hoping I can learn what may be going on with my TV. The TV is working just fine, however, when a screen shot of white clouds came on the other day, I noticed several dark areas as shown in my attachment. My first guess was maybe an LED issue, but then I though I should research a bit more.
Like I said, brand new to the site, pretty technical and not afraid to take things apart and repair, cars, PC's, etc.
Can someone please steer me in the correct direction?
much thanks,
Kent

[nomoresonys]

Re: Vizio M70-C3 Dark Spots

Sure looks like weak or burnt out leds in the backlights.

[Diah]

Re: Vizio M70-C3 Dark Spots

this VA panel i don't think so the issue with LED backlights to me the Sandwich layers of the panel are the issue.. wish i am wrong so you can safe it. take screen apart and check the back light id burnt or weak or some are off

[nomoresonys]

Re: Vizio M70-C3 Dark Spots

If you take it down to backlights be very careful not to force anything, the screen is very flimsy and breaks very very easily, those suction cups from harbor freight or ebay seem to work pretty good for the job also maybe check some youtube videos before you tackle it.

[jjanssen7]

Re: Vizio M70-C3 Dark Spots

The dark spots are too squarish to be sandwich layers. I think some of your backlights are out. It's sometimes possible to peak in a top corner to confirm (rather than opening the whole thing up), but as others have said be very careful. I've even snuck in one of those usb cameras from the backside on rare occasions.

[DXseekerMO]

Re: Vizio M70-C3 Dark Spots

What I would do is take the back cover of the TV off, locate each row of LED strips then compare their position in the TV to the on-screen position of the dark spots. I see two separate streaks of dark very close to one another. Mostways I've seen bad LED's don't seem to look like that.

Before scrapping the TV I'd pull the flap and check the backlights anyhow by leaving the boards on it, pull the flap and fire it up with the power button.

[jjanssen7]

Re: Vizio M70-C3 Dark Spots

I believe that model has local dimming, which means it has smaller individually driven strips. I'm guessing that when you open it up you'll find 6 or 7 strips with all or some LEDS not working. Just a guess though. I've done a few of those 70" C3's but it's been a while.

[budwich]

Re: Vizio M70-C3 Dark Spots

probably the "easiest" way would be to measure the voltages going to the strings and compare the results.

[nomoresonys]

Re: Vizio M70-C3 Dark Spots

probably the "easiest" way would be to measure the voltages going to the strings and compare the results.

+10 very logical.

[jjanssen7]

Re: Vizio M70-C3 Dark Spots

probably the "easiest" way would be to measure the voltages going to the strings and compare the results.

Just make sure there is a "full white" screen being displayed in case there is local dimming...

[budm]

Re: Vizio M70-C3 Dark Spots

Please provide the pictures of the whole backside of the TV showing all the boards, then good clear straight shot of the whole board of each board.

[mmartell]

Re: Vizio M70-C3 Dark Spots

If it has local dimming then the circuit controlling it may be faulty

[budwich]

Re: Vizio M70-C3 Dark Spots

since there seems to be a lot of areas... my guess is that you have been running the set "full bright" resulting in heating of the diffusers around the led resulting in some "burning" which has made them less transmissive. If the actual leds had problems, odds are high that the set would have shut down due to some form of voltage / current limits being set.

[Diah]

Re: Vizio M70-C3 Dark Spots

The TV is working just fine, however, when a screen shot of white clouds came on the other day, I noticed several dark areas as shown in my attachment

on the specification of the this TV there are full arrow dimming system. as other said. this panel are big the risk to take out with one person do high.

reading voltage don't work at all as its currents to dimming or turn off. if there was one burned then whole back light will be out and TV will never start.
the rest we can think what i said before.. but its much we can know more close with easy steps

1- make hard reset from service menu and check result

2- attached UHD learning full arrow dimming system put them on fat32 usb format and play them on the tv one by one until you can see the white one full White.

if no change please report to do other test

[kentkirchner]

Re: Vizio M70-C3 Dark Spots

HI Guys, thank you very much for the great feedback, much appreciated! Appears I should focus on a couple areas, LED's and the local dimming aspect of the TV.
I think a good place to start is where BudM recommends, take off the back of the TV and snap some shots of the entire back, then of each board up close. I'll try and get a peek at the LED's as well without tearing the whole thing down. I have watched and studied several YouTube video, including ShopJimmy.com of replacing LED's on a 70 inch TV and not ready to jump there yet. :-)
I think I understand Diah's post, but not sure what I am looking for or the result of the test. I did the following:
I went into the System settings and restored the TV back to factory defaults, is this what is meant by a hard reset? In my world, a hard reset is unplugging and plugging back in, which I also performed.
Now, his next step, put on a thumb drive and play the white and black back and forth until the white screen is all white?? and if it nevers goes to completely white?
Oh, one other question, the Vizio site said this TV does have local dimming in 32 areas. So I looked on ShopJimmy.com and I see an LED driver board with 32 components. Does this board control the local dimming aspect of the TV? Seems logical. So if the LED's are all good, maybe need a new LED driver board..sorry for the long winded return, but ya'll had great thoughts.!!

[kentkirchner]

Re: Vizio M70-C3 Dark Spots

Hello Diah, I restored the factory defaults and picture still the same. Next, I copied the black and white jpg's to a thumb drive and played them on a slide show for a couple minutes. I could always see the shadows when the white screen played.
Is that the tests you are asking for?
thank you,
Kent

[kentkirchner]

Re: Vizio M70-C3 Dark Spots

Please provide the pictures of the whole backside of the TV showing all the boards, then good clear straight shot of the whole board of each board.

Will post pictures this weekend...thank you

[nomoresonys]

Re: Vizio M70-C3 Dark Spots

Some say it's dirt n dust on the diffuser sheets.

[budm]

Re: Vizio M70-C3 Dark Spots

You have 32 LED strings, thus 32 power MOSFET's to control the current for each LED string. Using LED tester to look for open LED will be the easiest but you will have invest in the tool. Taking the LCD panel apart will be the last thing you want to do after all the testings are done.
https://www.shopjimmy.com/vizio-1p-1...led-driver.htm

https://www.shopjimmy.com/foxconn-s7...-16-strips.htm
Based on picture of the LED strip from SHOPJIMMY, it has 160 LED's total that I can see, so it means (if they are grouped equally) 5 LEDs per zone, you can use two 9V batteries connected in series to form 18V source than put 150 Ohms resistor in series to limit the current to about 30 mA for testing each set of LED.
5 LED's with current limit of 30 mA so total Vf of 5 LEDs = 2.70V x 5 = 13.50V.
18V - 13.50V = 4.50 V, 4.50V @30mA = 150 Ohms.
BTW, can you read the P/N of the LED driver IC U101, U102?

[budwich]

Re: Vizio M70-C3 Dark Spots

:-) very wise on the "last thing to do" especially as a "first effort". Ultimately, I kind of doubt that to fix this set, there will be an easy / board solution.