Re: Testing LG 47LN5700 backlight ps output w/ resistor

I would like to thank you, BudM and all the others for the invaluable assistance in getting my 47LN5700 repaired today. It was indeed one entire LED strip (L+R) that was out plus a single LED on another strip. I just replaced them all. Instead of buying an LED tester, I bought a Yescom 30V variable DC supply from Amazon, which is capable of a constant current mode. I was able to then test each pair (L+R) of strips (9 LED's) with about 24 volts and constant 50 ma current. I can use that power supply for general bench work and...

Re: Testing LG 47LN5700 backlight ps output w/ resistor



OK, thanks , Bud. Since I don't want to butcher the cable going from the LED driver output to the LED strips, suppose I swap the two LED drive circuits by creating a breakout on the PS/driver board from the points noted on the schematic attached here. With pigtail leads from these points I can easily swap LED 1 with LED 2, as you suggest.

I appreciate your diagnosis of a bad LED string earlier. This exercise is purely to convince me that I have no choice but do do surgery on the LED strips, whereas...

As a way to verify proper output of the backlight power supply in LG 47LN5700, is it a legitimate method to simulate the LED load with a resistor? I have the schematic and spec of the two LED outputs, which are each nominally 0.4 A. So I thought about connecting a 250'ohm power resistor to each output, just long enough to get a normal load voltage reading. Since it calculates to about a 40W load, it would be for only a short duration for a measurement on each output, since I don't have a 40W resistor. Access to the LED + and - is possible without bothering the connector, although the connector...

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...

Re: LG 47LN5700 Back light issue

I have the same problem with similar symptoms. 47LN5700. Board is EAX64905501 (2.3). Strips are LC470DUE SFR1. I should ask , though, whether there is any significance to the LED- test point (PS output connector) voltage. My LED+ voltages with or without strips connected rise to 100 volts initially and then bleed back to 78 volts. However, the LED- test points are both zero volts without a load, but with strips connected, ONE of the two LED- test points reads 19 volts and the other reads zero. With strips disconnected, both of the LED- pins read...

Re: New Members - please post your introductions here

New member. Own an LG47LN5750 that others seem to have had the same problems with LED backlighting that I am having. Hoping to learn and ask questions about troubleshooting. I have done electronics troubleshooting all my life but I'm new at trying to fix LED TVs. I like what I see so far.