Solved! LG UH5500 Backlight Keeps Burning Out Strips

[IWorkInPixels]

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 provides a spike of way too much voltage 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.

Could someone walk me through the basic steps involved in troubleshooting this and preventing my TV from burning out LED strips repeatedly? I think I need to do the following:
1: Locate the power output from the LED driver(s).
2: Measure the voltage (and amperage) on startup vs when the TV is on across those lines.
3: If the on startup voltage/amperage is too high, use ohm's law to figure out what size resistor to add to limit current to the LED strips.
4: Replace the burned out strips, put it all back together, and hope that the damned thing stops breaking.

Does that sound about right?

 

[IWorkInPixels]

Someone in another forum suggested that it's the current spikes when you start the TV that are the problem, so a couple of reversed biased zener diodes across the power rails for the LEDs would probably solve the problem.

 

[americanaudiophile]

Just using a resistor won't work because that will reduce the voltage all the time not just on startup. You would need an MOV or possibly a varistor.
https://www.electronicproducts.com/...tection_for_LCD-TV_backlighting_supplies.aspx

 

[IWorkInPixels]

Just using a resistor won't work because that will reduce the voltage all the time not just on startup. You would need an MOV or possibly a varistor.
https://www.electronicproducts.com/...tection_for_LCD-TV_backlighting_supplies.aspx

Yeah that was the idea... using a resistor so that even when the backlight setting on the TV is set at 100, the actual power to the backlight would be like 70% of that, thus improving the life of the LEDs. This is necessary because the backlight setting will revert to 100 every time the TV loses power, and then there's no way to set the setting low before turning the TV on again.

But... there's also the current spikes to deal with, so I'm thinking a couple of zener diodes reverse biased across the power rails might be needed so that we regulate the voltage down to whatever the nominal voltage is supposed to be for each LED rail.