LG 47LN578V-ZE backlight trips out

[Simisker]

Lg logo comes on for a split second then the backlight goes off, the tv stays powered though, looked at the power board and no caps seem dead...

[Davy]

Got a feeling these are LED backlights not CCFL's.... Make sure Inverter board is well soldered, especially around the transformers.  The leds can and do go, become intermittent or dry jointed.

Since you mentioned the power stayed have you tried connecting an antenna or some other input signal, do you get sound? Another trick is to get a bright flash light shine it on the screen and look at 30 to 45deg. angle you might see a feint ghost looking image of a picture - this obviously pointing to a back light problem.

From memory there are two banks of 27 series connected LED's... 'I think' Charles Hyde & Son does them.... don't be surprised if one or more are faulty.

Dave

[jordan]

Control LED diode into the panel

[Simisker]

Yea it is def the back light because I can still see an image on the screen, what are the led bulbs like to change?

[Simisker]

Which is the control led diode jordan?

[jordan]

We need to open the panel and see which diode is burned

[Simisker]

Just stripped the panel and only 3 of the 6 led strips work, 2 3 4 but 1 5 6 dont? Is there away a can test the led strips with my multimeter?

[Turnip]

Hi Sim,
Usually if a strip doesn't light it's a burned Led joint or an O/C strip connector. Just pop off the lenses and have a look, as strips are usually connected series/parallel, one O/C led knocks out the entire string.

Can power up individual strings with a current limited P/S (or a resistance on series to hold down the max current to a few m/a) set at about 3v per Led (Sorts the duff one)

Best of luck - Chris.

[Simisker]

Ive narrowed it down to the bottom strip, if I bypass it all the other leds work, there is 2 dead leds, led 5 and 8 and I think 8 is the culprit for the tripping, all I need to do now is figure out the easiest way to change the smd leds since I dont have any other strips spare

[Davy]

Try Chas Hyde & Son   http://www.chsinteractive.co.uk/ or TV parts  http://www.lcdparts.net/xb.aspx.
You don't want to go by-passing them for obvious reasons.... just like by-passing crimbo tree lamps better to lob a couple of volts across each one.

Did I mentioned crimbo tree lights?
I think I was about 6 when I tried that trick, I lobbed silver chocolate foil in as I took them out... guess what, they got brighter and brighter - that's when I got my first 240V tingle.... wasn't shocking but just a tingle. Luckily my sister put them all back before dad got home.

Dave