LG 47LN5400 TV screen problem

[abduct]

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 main board, power supply, tried 3 different tcoms, and even swapped out a majority of the cables + ribbons yet the problem still persists.

I can only imagine that the LCD boards are broken, or the white plastic is inverting the image.

The menus are also almost impossible to see so I can't reset the picture settings, but I'd assume after the mainboard swap it would be using different settings.

Any suggestions?

Thanks

Edit:: Just now discovered that while playing through the menus one of the menu buttons causes the screen to go a lighter shade of grey and produce moving scan line like bars moving top to bottom, then it goes back to a dark screen with snow static.

Edit:: When removing one ribbon to the LCD it produces half a screen of pure white, and the other half black with rainbow colored vertical lines. When unplugging the other one, I get a black screen with a lighter black rectangle in the middle going vertical. Menus did not work with either cable unplugged.

[mmartell]

Re: LG 47LN5400 TV screen problem

If it was working before you fixed the leds it sounds like you may have broken the panel to get to them.

Try reseating all ribbons and cables again.

[abduct]

Re: LG 47LN5400 TV screen problem

If it was working before you fixed the leds it sounds like you may have broken the panel to get to them.

Try reseating all ribbons and cables again.

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 swapping the LCD for one from a known working set to see if it is infact the LCD/LCD drivers (the pcb's that the t-con connects to) but with extinguishing my extra parts (3 main boards, 3 tcons, 2 power supplies) and still yielding the same results makes me think it is definitely something with the LCD panel.

Is there any way to check if anything is bad with them (resistors or caps) or anything in particular I should look for? I looked for damage and such, but found nothing.

Also are the ribbons connecting the LCD to the LCD drivers supposed to be burning to the touch? Within a few seconds of powering the screen they are so hot I can't touch them for more than a second without being burnt.

[mmartell]

Re: LG 47LN5400 TV screen problem

I don't think they should be that hot. You could try the half-tcon test again and see if one side is causing them to get that hot. Maybe you have a shorted or otherwise failing cof.

[jason123]

Re: LG 47LN5400 TV screen problem

Does anyone know what LEDs (as in LED chip / component) should be used on the 47LN5400 backlight strip? I have the same issue as almost everyone else, and I would like to replace the LEDs myself. I just don't know if that's a good idea or not, and I don't know the LED chip part number to use. Help is much appreciated.
Thanks

[120volts]

Re: LG 47LN5400 TV screen problem

You can get them on eBay
My 47LN5400 also had bad LEDs and as I was testing the LED strips I accidentally blew two more strips with to much current/voltage.
I forgot to set the current limit on my power supply.

Now I don't hink I want to spend $100 for four strips.

Have Fun

[jason123]

Re: LG 47LN5400 TV screen problem

After many trials, I found the correct part number to be used as an LED Chip for this LG TV. I found it on AliExpress (Chineses Amazon.com) You want the 3528 Package Size

LG LED Backlight 1210 3528 2835 1W 100LM Cool white LCD Backlight for TV TV Application

These are identical parts to what LG TVs (at least 47LN5400) uses. You'll wait 30 days to get them, but they're $11 for a quantity of 100 or so.. good deal. TV repaired and works well.

MODEL NAME : LATWT470RELZK LED
Forward Current (IF ): 400mA
Pulse Forward Curren t1 (IFp): 650mA
Reverse Current (IR): 25mA
Reverse Voltage (VR): 0.8-1.2V (5mA)
Power Dissipation (PD): 1460mW
Operatin Tgemperature (Topr): -30 - +90 °C
Storage Temperature (Tstg): -40 - +100 °C
Soldering Temperature (Tsld): Reflow Soldering:260 °C
for 10secs

Hand Soldering:350 °C
for 3secs

Junction Temperature (Tj ): 135°C
Forward Voltage (VF): 3.05-3.65V (250mA)
Luminous Flux (LM): lm (20mA)
Luminous Intensity ( IV ) : 23.5cd (250mA)
Wavelength (nm) : -nm mA
CIE : x=0.2960 y=0.2770 (250mA)
Color Correlated Temperature (CCT):
CRI : 80°
Viewing angle : 120°
Lead Frame Type LED Package: 3.5x2.8x0.60mm LxWxH d=2.0mm

[budm]

Re: LG 47LN5400 TV screen problem

These?
http://www.aliexpress.com/wholesale?...=LATWT470RELZK

Please lets us know how it works out for you.

[jason123]

Re: LG 47LN5400 TV screen problem

These are it.. TV is repaired and works great!

[budm]

Re: LG 47LN5400 TV screen problem

OK, thanks! I may order them to play with.
The lights color is the same as the original?
BTW, no problem with ALIEXPRESS? I heard some people has some fraud charged to their cards after using Aliexpress.

[jason123]

Re: LG 47LN5400 TV screen problem

I think the part itself is the same as original. Yes, the cool white is the same .. you can't tell the difference. Pain to solder onto the board. You have to control your heat as these don't seem to have a true "Package"... you heat it too much and it falls apart.