LG 42LN575V backlight issue.

[Darkstar_]

Re: LG 42LN575V backlight issue.

Sorry,

The figures for those P801 pins are (from top to bottom based on picture I just uploaded).

All readings fluctuate between two values:

214/231
34/74
39/105
45/80

Another dumb question, I didn't realise there was a second set of pins to test.

How can I test them? I tried removed the cable connected in there, but I assume the cable must be connected for the TV to function to a level where I can test it (the power button for example).

I could remove the board completely, but then it won't be grounded?
Again, apologies.

[vinceroger69]

Re: LG 42LN575V backlight issue.

that connector goes from the psu to the main board it may be easier to measure readings there just push the red lead probe down the side of each wire in turn it will touch a metal pin and make contact ok

[dick_barton]

Re: LG 42LN575V backlight issue.

Don't worry about those readings. From the readings given for the led connector it looks very much like you have an Led fault(s).

At this point do a search for testing leds as there are plenty of helpful guides on this Forum.

There are also plenty of Youtube video's which are useful aid to finding faulty leds.

https://www.youtube.com/watch?v=K_VfM4grw3I

[vinceroger69]

Re: LG 42LN575V backlight issue.

just be really carefull with the strip down as the lcd panel is very thin and easily cracked also keep all the sheets that are under the lcd panel in the correct order and try to keep dust/dirt finger prints to a minimum as may show when you have the tv working again.

[dick_barton]

Re: LG 42LN575V backlight issue.

There are 10 leds per strip (2 x 5 leds per strip) and 5 rows in total = 50 leds
Each led requires 3V to operate so 50 x 3 = 150V to operate them all (board says 157V)
so the led readings at the connector should be in the order of:-
150V
120V
90V
60V
30V


https://tinyurl.com/z27dmxp

[Darkstar_]

Re: LG 42LN575V backlight issue.

Thanks guys for all your help.
While I am basing this on your initial diagnosis, I think I will write it off.
I don't have the patience to strip it down and test the LEDs, I really don't.
Nor do I have the money to purchase a power supply to test it and then £65+ for the strips.

We shall save and get a new one, if this has happened once before with this LG tv, it could again and I would rather cut and run.

I have learnt some good things doing this and I do appreciate the time you guys have taken to respond to my post.

It may disappoint some to know I am just giving up, but I really don't have it in me.

[vinceroger69]

Re: LG 42LN575V backlight issue.

well a battery can test the leds and if you can solder you can buy just buy the leds and swop them easily enough so could still be a very cheap repair if you have time i dont have a tester i use a old atx power supply sometimes or just a battery pack and multimeter.

[dskall]

Re: LG 42LN575V backlight issue.

Well you can take it apart down to backlights, power it on and they should flash and tell you which are bad. Buy one strip to use to repair the bad led's. Very low cost repair.
If you buy new tv turn backlights down as low as possible as all TV's with led's are susceptible. A new tv may fail in a year or just out of warranty

[dick_barton]

Re: LG 42LN575V backlight issue.

I agree with dskall and vinceroger69.

The website was just to show you the led strips.

You can buy individual strips off ebay once you have the part numbers needed after lifting the lcd panel. It could just be that one strip has faulty leds so £15 to repair.

Or if there are more than 1 strip with faulty leds you can buy one replacement strip and use the leds from that strip to replace the faulty ones.

There is plenty of information on how to do it but you do need to take care when removing/replacing the panel.

You could get in touch with Flocko (on this site) and buy some stackable leds from him.

[sordids999]

Re: LG 42LN575V backlight issue.

hi guys this tv im working on has no backlight

led + connector 104 volts steady
led _ connector 3.50 volts steady

main capacitor 322 volts

legend voltages seem ok but no 12v voltages on the tcon board fuse (swapped the tcon board with a working one still the same )

thanks

[attainteddragon]

Re: LG 42LN575V backlight issue.

pfc voltage looks low to me.

you could jump the ps without the main attached to check the ps and backlights to start with.

[sordids999]

Re: LG 42LN575V backlight issue.

##UPDATE##

luckily had a replacement 42ln613v main board tv all working again and in test mode

[sordids999]

Re: LG 42LN575V backlight issue.

no back light
legend P201 voltages seem ok
main caps 322 volts
LED + fluctuates to 210 volts then goes back to 230 volts always fluctuating
LED - fluctuates to 91 v then back upto 110 volts always flucutating

any ideas guys

[sordids999]

Re: LG 42LN575V backlight issue.

no back light
legend P201 voltages seem ok
main caps 322 volts
LED + fluctuates to 210 volts then goes back to 230 volts always fluctuating
LED - fluctuates to 91 v then back upto 110 volts always flucutating

any ideas guys

#UPDATE#
two shorted LEDS testing now

[sordids999]

Re: LG 42LN575V backlight issue.

i recently repaired the led`s but i have now noticed in the top hand right corner there is a dark patch about 2 inches in size and it will flash from time to time

has anyone experienced this before ?

thanks

[vinceroger69]

Re: LG 42LN575V backlight issue.

probably another failing led

[sordids999]

Re: LG 42LN575V backlight issue.

yes that what i was thinking ill strip it later then update

thanks

[vinceroger69]

Re: LG 42LN575V backlight issue.

I have now been replacing all the leds in a tv when i have any too repair then turn the back lights down i know this takes more time but its also a risk removing the panel again then again to replace another led and the lcd tab bonds may get weaker too.

[lysy]

Re: LG 42LN575V backlight issue.

Hi

trying to fix 42LN575s with no backlight but still can see picture with flashlight.

Here are my voltage testing:

When led unplugged (1 led+ 2 led- 3 led+ 4 led-):

1 220-235V
2 0V
3 0V
4 0V

When led plugged:

1 220-235V
2 140-160V
3 130–150V
4 95-115V

Cap 335V

Would that still looks like bad led strip? even if pin 1 voltage is more than specs?

thanks

[zomi]

Re: LG 42LN575V backlight issue.

I have now been replacing all the leds in a tv when i have any too repair then turn the back lights down i know this takes more time but its also a risk removing the panel again then again to replace another led and the lcd tab bonds may get weaker too.

Have you had any back since doing this ?