Backlight Polkadarks

[smort]

Soooo, I found someone giving away their 70" Vizio TV because it wouldn't turn on. Hoping it would be just some bad caps, I snapped it up. No dice. No bulging caps. TV would start consuming about 7W immediately after plugging it in, but no response from the remote or power button. Thermal showed the main chip on the mobo getting warm and nothing else. Power supply appeared to deliver stable 12V to the mainboard.

I ordered a replacement mobo(actually both mobo and PSU just to be sure) and popped it in. Picture! Sound! Endorphins! Then I noticed three long dark strips. Hmmm, had to be bad strips. Instead of just ordering a full set of strips, I ordered 1000 LEDs from China. Because what says fun like spending hours SMD soldering dozens and dozens of 3030 packages and saving $20? Well, more like $13 because I had to buy a proper hotplate. I mean, if we're going to call one of those 5CM square $7 aliexpress hotplates "proper." I wouldn't. But anyway. After spending several hours fixing the hotplate, because it was most definitely not proper, I was ready to rock.

I snapped off the lenses to prepare to swap the LEDs. I started to go too fast and I did this while handling one of the crunchier strips. The strips in the middle of the TV were visibly yellower than the surrounding strips, and the lenses were more brittle, too. I obliterated one of those crunchybois. I ordered a set of PCBs with LED and a lens for like $7 on papa bezos' site. I was able to snap off the lens and glue it on the original strip. The result wasn't too bad. It wasn't perfect, but it was better than my first attempt where I tried to use a lens from a Samsung. I also tried a Samsung LED with the Samsung lens and that was even more noticeable, so that's when I got the pack of PCBs with lenses.

After putting everything back together, exactly the way it came apart(I taped the filters) I am greeted with not 3 very dead zones, but 144 dimmer zones. I didn't notice it right away, but as soon as it went to a monotone solid color it was like BAM. I put a JPG on a thumbdrive that's solid 127127127 grey, and here's this:

[smort]

I saw some people on youtube use white nail polish after soldering. I did not do this.

Also, the new LEDs are about 0.2mm thinner than original. I didn't really foresee either of these issues causing a huge problem like I have.

[Diah]

the first solid reflector you installed in wrong way.. the smooth surface should be on the top... now its down side facing the LED

[smort]

So, the thick sheet, closest to the LEDs should have a different surface on each side, and the smoother of the two should be facing the viewer. Ok. I thought I taped everything. Nothing is impossible right now, tho, because the living room is in chaos, and this repair has been weeks in the making(giving pieces time to get unintentionally shuffled around). I will give it a go in the morning.

[smort]

Both sides of the thick panel appear to have the same surface quality. On the side that was facing the LEDs, I've noticed a pattern print.

[nomoresonys]

That's just a mess, best way to go and easiest is get the correct strips in there.

[smort]

Since this is more of a learning opportunity, now, than anything else at the moment, I'd like to find out why what I have isn't working, then go from there.

[nomoresonys]

Well if it isn't something already mentioned, it could be wrong led type, wrong orientation of lenses when reapplied. Not sure I followed what lenses you used but could have been wrong ones. That's why it's best to just order the correct strips for the tv.

[smort]

I know just getting the pre-made strips is more sensible.

I had to know what was happening here, so I popped in one of those lone backlights you can get a pack of. Just the light source it should be. Bright, then gently falling off. I snapped the lens off and painted around the LED, glued the lens back on, and stuck it back under the diffuser thingies. So now I have to snap all the lenses back off and paint around the LEDs.

[Storyteller12]

First, quit trying it hack the tv together with misc. parts.
order the right leds strips and install. Yes it's more money but not wasting time like your doing now. (Time is money)
Put the tv back together with the diffusers in correct order and done.

The led lens covers have to be centered perfectly and you need to use the original lense covers. There designed for that tv. The spacing and depth of each led is specific to that tv for even lighting.

[smort]

Everyone saying just get new strips; you're not wrong. However, what's wasting time depends on your goal. I want to know how these lights work, and specifically why mine don't work(right now).

If you look on Craigslist or whatever classifieds, you can find people giving away perfectly good TVs. If I just wanted to watch TV, that's what I would get. Or, buy one of the ones someone's selling that's already working. Yesterday, I saw someone selling a Sony 75" 4K that's 2-years old for less than the time and effort of just having gotten new strips to begin with, for this TV.

Storyteller12, you're also right that different lenses are different. I already discovered that Samsung parts are notably different than these Vizio lenses and LEDs. I do feel that the lenses I got to replace the one I crushed look incredibly similar to the original lenses. And the LEDs that came with those(even though I have no plan to use them) have an identical light emitting surface area. The Samsung LEDs have a comparatively very tiny emitting surface and I have not seen the bare LEDs for sale anywhere. I saw some packages that looked identical on aliexpress, but they emitted straight up royal blue, which you do not want, even though they sold them as "TV backlight LEDs". So I think in the case of that particular Samsung TV, complete set of strips is the way to go. What's interesting is that Samsung TV I scrapped did not appear meaningfully thinner than this Vizio.

Storyteller12, you're yet again correct that alignment of the lenses to LEDs is important. I think I'll borrow a connector from the TV so it'll be easier to plug in each strip to my MT3608 which I've been using to test the strips after replacing the LEDs. With the connector from the TV, I won't have to hold power to the test points, I can just concentrate on aligning the lens while the glue cures.

So, I've already got the reflector sheet out, as well as the pin snaps that hold the strips. All I have to do is pick up the strips, snap the lenses off once again, paint the areas around the emitters, then glue the lenses back.

[momaka]

Jeez, why are all of the replies here so aggressive?! (Or at the very least, too direct & rude.)

smort : I enjoyed reading your post here very much and curious to find out how you end up fixing this issue. It's not a "waste of time" if you're learning... and even more so, when you are posting your findings online so that others can learn from what you did.
FWIW, fixing TVs these days ain't worth it whichever way you look at it, and especially as a business. So like you said, if you wanted a working TV, you wouldn't have bothered getting a broken one in the first place.
But from a "keeping less things in the landfill" perspective, it is a worthwhile endeavor.
Anyways, glad I didn't post the repair of 55" TCL TV I did a few years back, because I probably would have gotten ripped to shreds with the way I cobbled that "fix". (But just for the record, I used a regular 10 mm through hole LED in place of the original... so there's a very faint "bright spot" on the screen. My parents can't see it at all, even though I've pointed it out to them... so all good? )

[nomoresonys]

None of these replies are aggressive or rude. You must be reading that in yourself, does anyone else see the replies in that fashion? Because I doubt anyone meant it to be, correct?

[smort]

I don't think anyone "likes" being told what they're doing is a waste of time, and while I can see how someone might be miffed by being told that, it's valid criticism if it comes from a place of trying to help. I sort of poke fun at myself in the first post for taking the long road around by not getting original strips and soldering dozens and dozens of LEDs, but it's maybe a wall of text I'm not sure everyone read? I think if anyone else comes in here and says "what a waste of time", then that would be super redundant. I think at this point in history what I'm doing, where I am in the USA, might be a waste of time. There may be places in the world where it's not. There may be a point in the future when it's not a waste of time, anywhere.

Back to the topic. I made a stencil type thing to theoretically speed up the painting so I could use spray paint. Not sure it really worked out. I started with just a single strip to see how things would go. Why do all 144 LEDs is what I'm doing isn't even going to work. So, I used a woodworking chisel to flatten the lens feet glue blobs on the strips to maintain the original LED-lens distance. I did this the first go around, too. Anywhere the chisel scraped the solder mask, the surface became paint-phobic. Didn't see that coming. Also, I got paint on a couple LEDs so i had to take a toothpick and clean the phosphor gently. I made the part of the stencil that touches the LED so it would have positive pressure to reduce the possibility of this from happening, but it wasn't enough.

[nomoresonys]

Surely, as long as a body is enjoying what they're doing then it's time well spent.

[Diah]

my bad.. i just read the first post again.. and found you just replaced LEDs not the strips... no one can succeed to put the lens back in place Only the robot.