LED Backlight Mod

[london-freddie]

Hi guys asking for help advice, I have got a family members LG tv coming to me in the next few days with failed backlight led or leds, I know it will be a failed led as I have now fixed this tv three times with failed leds, fix one led another fails after a time scenario, asked them to reduce backlight in settings
My question is it possible to install a resistor in the feed to the backlights to reduce the voltage going to the led strips, in theory maybe they will last a bit longer. Or am I wrong and it will make no difference or leds will not work.
Any ideas please

[budm]

Re: LED Backlight Mod

You can try looking for the LED driver IC spec, it may have control pin that will set the LED current, if not then you can increase the resistance of the Current sensing resistors.
https://www.badcaps.net/forum/showth...ED+CURRENT+MOD

[london-freddie]

Re: LED Backlight Mod

thanks for that budm, do you think it is a worthwhile idea to try and lower the current going to the led strips in order to try and make these failing leds last a bit longer.
I was rather hoping that I could just put a resistor in the feed wire/s from the board to the backlights, is that not possible ?

[budm]

Re: LED Backlight Mod

The LEDs are driven by constant current circuit, simply putting the resistor in series with the LED string is not practical since the power supply will try to maintain the current flowing through string, so modifying the feedback circuit is easier or modify the IC current setting, if it has one, will be better.
Some TV you will have to make sure that the backlights level are set for each input source.

[london-freddie]

Re: LED Backlight Mod

Thanks budm, not as easy as I was thinking this one, may have to just keep replacing the leds as they fail,

[mu2]

Re: LED Backlight Mod

Hi,

I've modified a couple of LG 50LN5400 sets for myself that use the BD9483F chip.
The spec sheet is here:
https://www.rohm.com/datasheet/BD9483F/bd9483xx-e

If you read the specs you will find a formula to determine the current allowed to flow through the leds. Raising the resistors will lower the current.
The boards that I modified had an array of surface mount resistors near the chip on the bottom. I'd suggest measuring those resistors and see what those values yield in the current formula.
Your board may not use this same chip.

I don't have enough experience to say that it extends the led life. I can say that I did not notice any significant decrease in brightness after the mod.

Mike

[Agent24]

Re: LED Backlight Mod

Best option maybe to change the LEDs for higher power ones, that can handle the current better?

[Andrew F. Ali]

Re: LED Backlight Mod

I have found that if I have to replace LEDs on a strip or strips more than once, it would be better to replace ALL the strips with new ones. Just turn the backlights down to 60 for all inputs. The LGs have different backlight levels for each input, so ALL inputs MUST be re-adjusted to the lower level and that will save your backlights in the future.