Onn 100012588 backlight issue *Solved 70 inch

[EazyBone]

Had another one of these 70 inchers from onn and was same problem as others. The picture shows but no backlight. The backlights test fine. The issue is the 450v 10uf capacitor by the backlight connector. Usually the cap bulges, the cap I replaced today for fix was NOT bulging. Replaced anyway and fixed.

Hope this helps someone.

[dcapper]

Is this a common thing? My Onn same model number is acting up. It turns on and sometimes it flashes the Onn picture and turns off. I tried hard resets and nothing helped.

[nomoresonys]

If not able to test caps, just switch those 2 out, be sure the polarity is correct, that's one pretty simple way to either fix it or eliminate them from being the issue.

[EazyBone]

To me it's common. Ive had 6 of these and it was always that capacitor in the picture. There's only 1 capacitor also.

The cap should be slightly bulged, but I have also seen flat ones, and replaced it anyways and that's what worked

2023 version of this TV, which is same model number, has a cord that is not removable, I've had an issue with main board, but the TV appeared to be dead, so different problem.

I would be safe to say that yes this is your problem.

[nomoresonys]

Right only one on this tv, some tvs have 2, one for each side.

[dcapper]

Awesome guys! I wanted the tv up and running fast so I just bought some caps off Amazon. If it acts up again I’ll put in Nichicons, Rubicons, or Panasonics.

[DR12]

I recently came across this post and the description of the problem was identical to my TV's problem. The backlight will flicker for a quick moment when powering up the TV then stay off. After reading this post, I purchased a new cap and replaced the 450V 10uF capacitor. This didn't solve my issue and the backlight doesn't even flicker when starting up now. I can do several things to light up the LEDs, so I don't believe those to be the issue. What I'm curious about now is that your image shows the capacitor near the cable going from the power board to the main board. That capacitor is 470uF 25V.

Which one was actually replaced? Any other advice by chance?

[EazyBone]

It's the 10uf one. I think I've had 15 of them where it was that capacitor. On one of them it wasn't the capacitor but it was the capacitor AND the backlights.

What do you mean you can do several things to get the lights to light up? You have an led tester?

[DR12]

I don't have an LED tester, but I have noticed the following:
With the other boards disconnected from the power board, I can get the LEDs to turn on and stay on if I short the mosfet (source to gate).
With the main board connected, shorting the source to gate only turns on the LEDs for a couple seconds.
If I ground a digital multimeter to the tv chassis and connect my positive probe to the mosfet gate OR touch it to the top of the capacitor (resistance or diode mode), the LEDs turn on.

I am not great with electronics, but I wonder about the mosfet since shorting it lights up the LEDs. From my understanding, with the other boards disconnected, the LEDs should stay on when the TV has power and that doesn't happen.

[EazyBone]

Maybe there is some validity to this method.. but it sounds completely wrong. LEDs can be forced to power on.. it doesn't show that all of them are working it just shows that a bunch are working. I don't think you should be using that method and should be getting an led tester to confirm voltages.

When I first got the TV that was the cap and LEDs, I replaced the cap and was excited to see the LEDs turn on.. but they didn't. The cap needed replacing regardless since it was bulging, I never tested the LEDs. I then at that point tested them and found only 2 led was out. Each strand did 96v and 93v indicating one was out.

This TV was a absolute PAIN in the ass to change the LEDs as the deflector sheet is glued down with more glue then any TV I've ever seen. The next one I find that has this problem I'm taking the boards out and trashing it.

Anyway, not sure what exactly you need to do here except get a led tester and confirm your strips are fine. $15 on Amazon.

[DR12]

I was able to look at the screen and use the remote while it was lit up (although it is dim, suggesting LED brightness issues) and I noticed I have a purple bar along the left side of the screen. I'm attaching a picture. It looks like I have more than potentially just power board/LED issues. I'm currently debating my path forward as this potentially just got more complicated and expensive.

If I do get the LED tester, I see one of the voltages going to the LEDs is around 340V. The testers I'm looking at for 15-20 dollars only show up to 300V. Will that be an issue?

Thanks for all the help and patience.

[EazyBone]

The voltage from the tester will show only Around 96volts for thie tv. If the tester shows 300v then there's a short. It'll show a different voltage then if you tried to test it with multimeter. That bar won't be fixed by led replacement and if I personally saw that I would stop there. Looks like a cof like on the screen is damaged. Take a look at the ribbon on the bottom over there for damage.