LG 47ln578v

[samisat]

Hi,when I plug the tv in back light will come on for 1 second then goes off ,no light, no sound.thanks for your time.

[jordan]

Check LEDs in LCD display panel

[downunder]

Hi Sam,

If you strip the panel to expose the backlight LEDs, and remove to white sheet covering the LED strips,
you'll find each strip is extended by tacking another strip to its end, so as to make one longer strip out of two strip. It's the join that often gives trouble. You can solder a jumper across the connector to bypass it.
Remember, the LEDs in each strip are in series, with the last LED having a return path back to the pcb on the side where all the strips are configured.

Bruce

[chappers]

Hi, same set and same problem.

To save me time, can someone please explain the method to strip the panel for access to the LED strips?

Thanks

[downunder]

This video should give you the gist of it.

https://m.youtube.com/watch?v=Bf5T2wwtydY

[Southerner1959]

I have the same Backlight fault on an LG set . . .

The power to the LED strips from the PSU Board is only on for the short time the screen is on.

What I don't understand is HOW the screen can work perfectly for  about half a second on switch on, and again at switch off, if the LED strip is faulty?

Having said that, what would be the normal resistance measured using an Analogue ohm-meter of the LED strip?

(It looks a really difficult job to take the screen apart, so I'm trying to make sure this is the problem)

[kennyc]

Hi guys ,have had same problem with the 40 inch Toshibas . Never managed to get to the bottom of any of them . Strips are glued on . To be honest dont think they are designed to be fixed . They want customer to throw TV away and buy new one just like a kettle every couple of years . We all better start looking for other jobs

[zomikula]

Use a heat gun at around 200 to heat up the strips loosens the tape and they come off
Same to reapply
heat up the adhesive and when applying heat and push down.

If replacing single led this can be done insitu without removing the strip

[Turnip]

Hi Folks,

Just had one in where 2 Leds were S/C and one O/C. Replaced them and powered up with a bench supply finding all strings lit OK.

Reassembled without breaking the screen - Powered up, and after a brief screen flash it cut to S/by.

Powered up again - Straight to S/by. Checked Leds for a possible chassis leak - Nope. Disconnected feed to Leds - Cuts to S/by.

Bit puzzled - Any thoughts ? - Chris.

[tv tony]

Have this range of sets on the bench all day Chris. LED failure doesn't invoke stand/by.

[bonesy]

Hi Turnip,I might be talking out of my hat,but check that the electrolytics in the output for the LEDS,If the set has been laid on its back (panels to bench)the caps break away from PCB very easily,I've done it a couple of times,I think then set goes to st-by.Just a thought.

[bonesy]

Hi TV Tony,I know you repair a lot of LG products,just curious,do you change the strips,or replace the LEDS?

[tv tony]

Hello,
              I change the leds, using a leister hot air gun, you just have to be careful to align the lenses afterwards, 80% success rate 1st time, the amount of leds on each stick are staggered but I use a redundant laptop psu (19v) After splitting the strips. Obviously the sticks with 5 lamps on each stick will be dimmer. They can go s\c or o\c, the hardest part isn't replacing the lights, it's re-aligning the lenses. If you want the address for obtaining the leds I'll dig it out. They come in rolls of 1000 but cost peanuts.

[tv tony]

Just seen how much you pay for lamps Bonesy, a thousand for around £18.00, I'll find you the address.

[bonesy]

Yes please Tony.To start with I replaced all the strips,not cheap,but 100% no come backs.But I've started replacing LEDs then testing LED strip for brightness & overall even brightness,but the first two I fixed around two months ago by looks of it are coming back,LEDS failed again!Do you replace just the failed LEDS or all the LEDS on the strip?Also what do you use to refix the lens.I've been using a gel type super glue,which seems to work o.k.,some use clear silicon rubber.