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LG LED TV Baclkight Voltage Spikes
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

LG LED TV Baclkight Voltage Spikes

by iworkinpixels on Fri Aug 16, 2019 10:12 am

I bought a 65" LG UH5500 for $20 at a yard sale because two of the backlight strips were burnt out on the bottom right corner. Opened it up, replaced the strips, TV worked fine for a while... then a strip on the lower left corner burnt out. Opened it up again, replaced the strip in the lower left corner. TV worked fine for a while... now one of the ones I replaced in the lower right corner has burnt out again. I have 4 extra strips left to replace burnt out strips, but I found something the last time I was searching the internets and think it's the culprit... unfortunately I can't find it again so I'm asking here in case anybody here knows...

Apparently the reason strips burn out so often in LG LED televisions of that era is that when you turn on the television the LED driver sends a power spike to the LEDs for a short time. There was a guy selling modified LED driver boards in which he had installed some extra circuitry to prevent this, but I am unable to find his boards or any pages talking about them now.

I am capable of adding a resistor to the board if that's all that needs to be done, but I know literally nothing about the innards of this TV other than where to stick the replacement LED strips.

Before I give up on this television, is there anything I could do regarding modifying the LED power supply myself to prevent it from burning out strips? Would it be as easy as adding a resistor or varistor to the LED positive rail to suppress spikes on startup?

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Re: LG LED TV Baclkight Voltage Spikes

by adafruit_support_bill on Fri Aug 16, 2019 10:49 am

Not sure of the magnitude or duration of the spike in this case. But a large capacitor between power and ground will help absorb startup spikes from power supplies. That is what we recommend for Neopixel strips. https://learn.adafruit.com/adafruit-neo ... -practices

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Re: LG LED TV Baclkight Voltage Spikes

by iworkinpixels on Fri Aug 16, 2019 11:03 am

Thanks! I'll see if I can come up with an appropriate value capacitor and give it a shot!

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Re: LG LED TV Baclkight Voltage Spikes

by iworkinpixels on Fri Aug 16, 2019 1:37 pm

Someone on another forum I'm on said that it's not dirty voltage that's the problem, it's a current spike when you turn on the TV... so perhaps a couple of strategically placed zener diodes across the power rails for the LEDs is the way to go?

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Location: Forest Hills, NY

Re: LG LED TV Baclkight Voltage Spikes

by adafruit_support_bill on Fri Aug 16, 2019 1:49 pm

If it is a brief spike at power-up, a large cap will absorb it. If there are repeated or prolonged spikes, the cap will smooth them out somewhat, but a zener would clip them off at the zener voltage. You could use both.

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Re: LG LED TV Baclkight Voltage Spikes

by zener on Fri Aug 16, 2019 3:20 pm

If you can borrow a scope then you see the exact amplitude and duration. A MOV could be a solution possibly also, but it really depends on exactly what is happening. Lacking a scope, you could put a cap on one, a zener/transorb on one, a MOV on one and see which ones die or live. You have a few spares to play with. Then you can sell kits on eBay.....

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Re: LG LED TV Baclkight Voltage Spikes

by iworkinpixels on Fri Aug 16, 2019 7:55 pm

I have a scope... I'll see if I can get a good idea of how big and how long the current spikes are...

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Posts: 32
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Location: Forest Hills, NY

Please be positive and constructive with your questions and comments.