LG 42LN578V picture but no backlight

[nikonite]

My neighbour just gave me their LG 42LN578V that with a torch shows the image perfectly clear and crisp but the backlight is not working, I have also not heard any sound from it either. I presume the LED driver is built into the screen itself as it seems the PSU powers the backlight rather than a separate board. Can anyone advise diagnosis steps? I was going to buy a new Power board as it makes a little bit of a whistling sound but don't want to throw money away on a none repairable set.
Thanks guys

[newtothis]

Re: LG 42LN578V picture but no backlight

Always post pics of board and chassis

[nomoresonys]

Re: LG 42LN578V picture but no backlight

maybe check expected voltages on connectors on power supply, might be a label of expected voltages near connectors, as always be careful working with power supply, HIGH VOLTAGE, on primary side can be deadly.

[budm]

Re: LG 42LN578V picture but no backlight

https://www.badcaps.net/forum/showthread.php?t=39740

[nomoresonys]

Re: LG 42LN578V picture but no backlight

Crawley UK, interesting name for a town.

[nikonite]

Re: LG 42LN578V picture but no backlight

Pictures as requested. Crawley is a great place, not at all "creepy"
Thanks for any help offered

[nomoresonys]

Re: LG 42LN578V picture but no backlight

Pictures as requested. Crawley is a great place, not at all "creepy"
Thanks for any help offered

Your lucky then, my town is a little creepy.

[nomoresonys]

Re: LG 42LN578V picture but no backlight

do you have a digital multimeter for testing?

[nikonite]

Re: LG 42LN578V picture but no backlight

@nomoresonys, I do yes. I am not great with them though

[nomoresonys]

Re: LG 42LN578V picture but no backlight

can you see a label by your power supply connectors on the board? might say 3.3v, 5v, 12v etc.

[nomoresonys]

Re: LG 42LN578V picture but no backlight

you may want to try a different power board, sometimes they are pretty reasonable, the whistling could be from a transformer. even if its not the problem, and you get it at a good price, at least you have a spare, and can rule it out, as long as the one you buy is good.

[nikonite]

Re: LG 42LN578V picture but no backlight

I will buy a new board as they are pretty cheap used. It would be a miracle if it fixed it but a lovely surprise Will post back when it arrives. Thanks guys

[nomoresonys]

Re: LG 42LN578V picture but no backlight

no problem, let us know, it may help others with similar problem, good luck.

[nikonite]

Re: LG 42LN578V picture but no backlight

Ok the bad news:
PSU didn't fix it, there was a string of led's faulty when I took it apart
Good news:
I bought the same tv from gumtree (100 mile drive last night) with a cracked screen for £20, swapped my decent lcd panel over (probably some dust behind but oh well) and taddaaaa!

[nomoresonys]

Re: LG 42LN578V picture but no backlight

Glad to hear the good news, nice fix.

[ReeceyBurger123]

Re: LG 42LN578V picture but no backlight

Good news, thats the shame with newer led backlit sets they leds always seem to get too hot and fail seeing it too often

[nomoresonys]

Re: LG 42LN578V picture but no backlight

Ok the bad news:
PSU didn't fix it, there was a string of led's faulty when I took it apart
Good news:
I bought the same tv from gumtree (100 mile drive last night) with a cracked screen for £20, swapped my decent lcd panel over (probably some dust behind but oh well) and taddaaaa!

I'll bet that faulty string is what had your board humming.

[ReeceyBurger123]

Re: LG 42LN578V picture but no backlight

I'll bet that faulty string is what had your board humming.

Probably due to it current limiting.

[sordids999]

Re: LG 42LN578V picture but no backlight

i know this is proberly a no but i have this tv but it seems the crack is inside the screen would it be possible to buy the inside panel as a replacement ?

[nikonite]

Re: LG 42LN578V picture but no backlight

There is no 'inner' panel I'm afraid, just the lcd and then several plastic layers. You would need to replace the lcd panel and getting an undamaged one will be pretty difficult. Probably more than the cost of a second hand set.