Test LG backlight LED strips with external bench PS

[gliebisch]

I am about to disassemble an LG 47LN5700 to troubleshoot and replace defective backlight strips. It uses a total of 12 strips, half of which are 5 LED and half are 4 LED strip. I think a 5 LED connects to a 4 LED strip =9 and there are 6 so 54 total LEDs. The LED driver at the TV power supply has TWO + outputs.

I have a variable bench DC supply that goes up to 30 volts. Can I use this to test the strips once I break them down to individual strips of 9? If so, what voltage from the power supply should I use. My guess is that I'd use 27 volts. Is it 3V across each LED? I realize there is some paralleling of these, but I'd like to test individual strips since I only have 30 volts available from the bench supply. Also, should I use a current limiting resistor out of the bench supply?

Thanks.

[heavymachines]

Re: Test LG backlight LED strips with external bench PS

Yes use current limiter resistor. Unless you're using an led tester made for job.

[johns1mj]

Re: Test LG backlight LED strips with external bench PS

I use a model train transfomer that only goes to 18 volts. I figure 3 volts per led and use a multimeter to dial in the voltage. Depending on how the led lights connect you can use a jumper on the first strip to close the loop and straight to the second strip. Start low on voltage and you can move up to make it easier to see the lights. You will need to scratch the surface of the strip before and after the led to test individual leds. You can remove individual leds and solder in a replacement. I keep strips around just for splicing in leds.

[budm]

Re: Test LG backlight LED strips with external bench PS

Always use current limiter when testing the LED/LED strip.