Re: LG 47LN5400 TV screen problem



The state of the panel was unknown although I did the flashlight test and didn't see anything before I started the work. I've done 2 other TV's and haven't broken the panel, although they're flashlight tests confirmed they were working before hand.

As for reseating the cables and ribbons, I've done that many times and also tried using spares I've had and nothing. I've also tried bouncing around the fixed ribbons going from the LCD to LCD driver and the screen didn't flicker or change.

I've been contemplating...

I have a LG 47LN5400 TV with a screen problem. I repaired the back light as there were burnt out LEDs, so that problem is fixed.

The back lights turn on, and I can cycle the menus, but the menus show up almost solid black boxes and any text on the screen is backwards in a mirrored fashion.

The LCD is also very dim even with the back lights turned on.

Is the plastic what I call "diffuser" which spreads the light evenly some sort of polarization filter which if I installed backwards would cause such a thing?

I have changed the...

Re: LG 47LN5400 TV Backlight problem

Thanks for all the help guys.

It was easier than I thought to strip the TV down to the LED backlighting and I used my DSLR camera with extended exposure to figure out which LEDS were broken. I had 2 LEDS shorted closed, and 1 LED shorted open. The open led caused 1 entire LED channel to fail causing the PSU to shutdown.

Instead of buying new parts I simply scratched the solder mask off the PCB and soldered in a piece of wire to complete the circuit bypassing the broken LED's and using epoxy to secure the connection/insulate...

Re: LG 47LN5400 TV Backlight problem



That makes sense, but why would the normal 47" PSU be failing. These were all returned to the store, but I can't see all the TV's having a bad PSU causing similar or the same symptoms.

Is there a certain process I should take to confirm all the output voltages from the PSU as well as specific parts? I have checked the fuses and visually inspected for damage, but beyond that I haven't checked many of the parts.

What confuses me is if a LED did short or become open, which is causing the 47"...

Re: LG 47LN5400 TV Backlight problem



Is there a way to bypass this? Why does one power supply successfully make the TV work, and the original one does not?

Is it possible to cut the traces leading to the broken LED strip and solder a resistor onto the PCB tricking the IC into believing it is functioning properly?

I've gotten around to my other LG 47" which had similar symptoms and placing the 55" PSU in it as well fixed the problem, so that makes 2 TV's.

Is there steps to test all the outputs to the mainboard...

Re: LG 47LN5400 TV Backlight problem



These are the readings for the original PSU (Note I don't officially know which set of outputs are which I just gave them channel names to help analyses the data):

-LED + CH1 to ground goes to 76v then when the backlight attempts to turn on goes to 103v and ramps down to 76v
-LED + CH2 to ground goes to 76v and then 171v when the backlight attempts to turn on, then ramps down to 76v.
-LED - CH1 to ground goes to 20v, then 46volts when the backlight attempts to turn on, then ramps down
-LED -...

I have recently come into a bunch of TV's for cheap and they all need repair. I've had success with getting one working, in an odd ball way so I am here for advice or recommendations.

First the conditions of the TV's:

I have 3 LG 47LN5400, one LG 55LB5900 (broken panel) that I am working with (I have a few others 50" and 42" but they have broken panels that I am not going to bother with besides for parts.

The 3 47" LG's I am trying to fix all have the same problem. When powering on, the backlight comes on for a split second and turns back off....

Re: New Members - please post your introductions here

Hi all, I'm just here to pick the brilliant minds of those on this board.