LG50LN5400 Backlight Issue

[sgabrie8544]

Greetings!
I seem to have the "rare" (LOL) issue of the LED backlight being out also. TV powers on, Audio there, flashes quick and no pic. I can see it somewhat if i look on an angle and use a flashlight.
I removed the back cover and disconnected the connector from the Power/LED power PCB to the LED strips and I still read NO DC voltage at the 2 outputs of that connector.
Should I replace the Power/LED PCB or could it still be a LED strip?
THX
Steve

[sordids999]

Re: LG50LN5400 Backlight Issue

Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

[ReeceyBurger123]

Re: LG50LN5400 Backlight Issue

If you have no Dc at the Led connector with and with out Leds connected the Psu is at fault lol

On Lg's backlight WONT fire with out mainboard present.

[sgabrie8544]

Re: LG50LN5400 Backlight Issue

Output to the LED strips is the small white connector I removed and measured for voltage to the LEDs.

[ReeceyBurger123]

Re: LG50LN5400 Backlight Issue

So have you got a voltage then ?

[sgabrie8544]

Re: LG50LN5400 Backlight Issue

No, I measured at the 2 test points right under the connector with respect to their individual gnds, with the connector removed. I got nothing.

[ReeceyBurger123]

Re: LG50LN5400 Backlight Issue

Use chassis ground to measure the Led output.

[johnboy1313]

Re: LG50LN5400 Backlight Issue

You've almost certainly got one or more failed LEDs inside the panel. You're going to have to open the panel to see which ones are out.

[budm]

Re: LG50LN5400 Backlight Issue

You have two sets of LED drivers on that board so you need to measure the DCV at the LED connector as requested.

[sgabrie8544]

Re: LG50LN5400 Backlight Issue

Power on, Led strip connector out, chassis gnd to both those LED DC test points = no voltage! How common can that be, I dont get it.

[ReeceyBurger123]

Re: LG50LN5400 Backlight Issue

The ground on the Led goes through a return line so best to use chassis ground and we needed to know. Now you need to get us a close image of the Psu.

[budm]

Re: LG50LN5400 Backlight Issue

Closed up pictures of the power supply-LED driver board? I cannot read the P/N on the barcode sticker and on the board? LG EAY62810801 (EAX64905501(2.0)) Power Supply / LED Board?
How about the readings on all 4 pins of the LED connector?
Are these boards used in your TV?
http://www.shopjimmy.com/lg/50ln5400-ua

[Agent24]

Re: LG50LN5400 Backlight Issue

You say the screen flashes briefly at power on though?

I think you may need a dummy load for the PSU to test? It may not run normally with the LEDs unplugged either, as it may detect that as a fault condition.

[budm]

Re: LG50LN5400 Backlight Issue

'Power on, Led strip connector out, chassis gnd to both those LED DC test points = no voltage! How common can that be, I dont get it.'
Those two test points are the Cathode return side of the LED strings so youi not going to get any readings with the connector removed or if both LED strings have open circuit.
We need the DCV reading of the Anode side of the LED string which are fed by the boosted power supplies that is why we need the readings on all 4 pins (L+, L-, L+, L-) for easier determination the condition of the Voltage sources.
You will have to turn the TV on and off 4 times with the meter probe attached to one of the four pin at at time to catch the DCV when TV is first turned on and then after a few seconds later to see if the Voltage jumps up an drops down.

[sgabrie8544]

Re: LG50LN5400 Backlight Issue

Bought the TV new 18 months ago.
TE16A628108011322 (3.1)

[budm]

Re: LG50LN5400 Backlight Issue

LG EAY62810801
http://www.shopjimmy.com/lg-eay62810...pply-unit.htm#

Pictures provided by shopjimmy.

[sgabrie8544]

Re: LG50LN5400 Backlight Issue

Power on, connector re-connected, measured from chassis gnd to both pins on connector marked LED +, each one read 90V when powered on, then trickled down to 0. Shorts in the LED strip?

[budm]

Re: LG50LN5400 Backlight Issue

How about on the L- before the Voltage trickle down?
BTW, what is the Voltage rating printed on the C257?
It looks like the Boost converter circuits are working.

[sgabrie8544]

Re: LG50LN5400 Backlight Issue

Same thing, i held the probe on Led -, plugged in the cord, it shot to 98v then dropped slowly, other side jumped to 45v then dropped. thx for the help!

[budm]

Re: LG50LN5400 Backlight Issue

So the readings of both L- are not the same if I read your reply correctly?
If that is the case then you have LED problem.