Author Topic: Help with repairing a broken Vizio TV Backlight  (Read 445 times)

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Offline Randomuse

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Help with repairing a broken Vizio TV Backlight
« on: April 14, 2020, 12:19:33 am »
My Vizio TV recently went out and I wanted to try and fix it. It is a model E320i-B2. When I hold a flashlight to it I can see the picture. I also can hear audio from it. I know it has something to do with the backlight. When I opened the TV up I saw a capacitor with a triangle shaped bulge on the main board. I don't know what kind of capacitor I should get to replace it, but I think I need a 25v 470uF capacitor. The bulging capacitor is pictured here. Is this correct?
 

Offline TheMG

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Re: Help with repairing a broken Vizio TV Backlight
« Reply #1 on: April 14, 2020, 01:57:19 am »
That doesn't look abnormally bulged to me. Those lines you see on the top are pressed into the capacitor casing during manufacturing. This creates a weak point so that if the pressure in the capacitor exceeds safe amounts, the top of the casing will split open and vent out instead of the capacitor turning into a miniature rocket with a loud bang.

You should measure the capacitor (capacitance, and also ESR if you have an ESR meter) to determine its health, as there don't seem to be any signs of physical distress.

Don't forget to check voltages! That means all power supply outputs for proper voltage and low ripple. Also the LED backlight driver output voltage.

All that being said, a non-working backlight is more often than not caused by bad LEDs in the backlight. However, it's not always easy to determine if the LED array is faulty or the driver circuit, because many drivers will stop outputting voltage if there is an issue with the LEDs causing the current and/or voltage to be outside of the programmed tolerances, so the lack of output voltage from the driver does not necessarily indicate a problem with the driver.

You can test to see if you can measure a brief voltage spike on the LED driver output when turning on the TV. If there is, then most likely the LEDs are at fault. Note that if your multi-meter is too slow, it might not be able to "catch" the driver briefly turning on.

Note also that the LEDs are normally arranged in series-connected strings, meaning the voltage required to light them up can be pretty high (up to a few hundred volts on some TVs). This means testing the backlight by powering it with a common bench power supply isn't likely to be feasible.
 

Offline james_s

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Re: Help with repairing a broken Vizio TV Backlight
« Reply #2 on: April 14, 2020, 04:53:56 am »
I've fixed three TVs with bad LED backlights and in every one of them it was one or more bad LEDs themselves. Two had multiple separate circuits and the backlight would come on briefly and then shut off. My main TV that I use now has all the LEDs in one long string and after one developed an intermittent connection it burned up and went open circuit.
 

Offline Randomuse

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Re: Help with repairing a broken Vizio TV Backlight
« Reply #3 on: April 14, 2020, 06:53:59 pm »
I tested the output voltages on the power board but I don't know how to test the output on the led driver since none of the terminals are labeled, and they are too small for me to measure them accurately. What should I do from here?
 

Offline james_s

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Re: Help with repairing a broken Vizio TV Backlight
« Reply #4 on: April 14, 2020, 08:46:41 pm »
You might be in over your head with this one. You need to figure out how the LEDs are wired, often they are in four or so separate series strings. If it turns out there's a problem with one of the LED strings it is a real pain to get to them in most cases, you have to disassemble the whole panel, a very fiddly job.
 

Offline Randomuse

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Re: Help with repairing a broken Vizio TV Backlight
« Reply #5 on: April 15, 2020, 01:30:44 am »
So would I just be better off hiring someone to fix it?
 

Offline Shock

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Re: Help with repairing a broken Vizio TV Backlight
« Reply #6 on: April 15, 2020, 01:15:36 pm »
Watch some youtube videos on LED backlighting repairs. It's one of those repairs if you aren't careful you can crack the panel or tear the bonded tabs etc.

If you take it to a repairer you want to make sure they can do backlighting LED replacements or know how to check backlighting and boards properly. A lot of TV repairmen are board or panel swappers.

It's a time consuming repair and it can reoccur so you are best turning your backlighting down so it lasts longer. Anyway no offense, but Vizio always seemed a low end brand to me. At the end of the day any brand and model can fail but some are more uneconomical than others to repair.
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