LG 50LN5406 - flashes shortly - LED backlight defect

I finally got my hands on one of the LG trouble children. The TV flashed the LG logo very briefly and then switched off again. The seller had a repair shop diagnose it and they said that the LED backlight was broken. Their repair offer was 320€. Wow. That's more than the used price of this device.

The LG of this age all die sooner or later due to one or more dead LEDs. The backlight in standard setup is too aggressively set up and they overheat.

I did not bother measuring anything and went straight on to a backlight repair.

Back cover off, nothing spectacular to see:

Step 1: Remove the front bezel:

Step 2: Unscrew the metal panel bezel, unplug the flat cables from the TCON board and carefully slide the buffer boards out of their seat:

Step 3: Remove the panel. This is the most delicate part of the operation. A 50 inch panel bends a lot when not handled correctly. I always wear gloves to avoid finger prints. Do not force a blade or similar objects between the panel and the frame to get a grip on the panel! A simple trick is to first unclip the black frame, raise it a little and then reach under the panel. That way it is easy to lift the panel with one arm diagonally supporting it from below and the other hand holding one edge to keep bending under control.

Be careful with stuck buffer boards. Make sure they slip out without force.

Step 4: Remove the panel frame and the foils. This is simple. Just wrap a tape around somewhere to keep them together.

Step 5: Remove the reflector sheet to get access to the strips. The four plastic standoffs come of easily when you squeeze them with pliers from the backside.

Okay. Measuring time! A good strip settles at 27.4 Volts. The bad strip yielded 36.1 Volts and it was obvious why. One LED was dead.

I removed the right half of the strip with a spatula, taking care of the double-sided adhesive tape, which will be reused.

Now, my new preheater got something to work on. The plan I had was to heat the strip up until the LED's solder would melt. Nope, not working. The material is too thick and a large copper trace shielded the heat from the top. Anyway, the lens came off very nicely under heat. The LED was so heavily damaged that it broke into crumbles. I removed what was left of it with the iron.

This looked terrible. The cathode pad was burned black all over. It almost seemed as if the soldering went wrong on this one and it heated up too much.

I cleaned it with a fiber glass pen and some Isopropanol:

This looked much better. Next time I will remove the sticker, too, before I work on the LED :-P

The SEOUL 2835 3V 1W fit perfectly. I put some leaded solder on the pads and the strip back on the heater. With just a short heat shot from the top with my heat gun at 260°C the LED snapped into place by itself on the molten solder.

Click here to buy the original LEDs. The LG Innotek LEDs perform identically to the SEOUL, but some might feel more comfortable with the exact match.

I glued the lens with plastic glue. Super glue did not quite do the job.

And here we are, all shiny and new! The new LED was indistinguishable from the others:

Evangeline Lilly is looking happy!

What to do to prolong the life of this TV

Turn the backlight intensity down to 50%! The image is still good enough and the LEDs are substantially less under stress.