LG 42LE4500 Losing Backlights

[newtothis]

I have noticed a couple of threads referring to this model but no real answer.

I picked up this set with the description of it switches itself off... After getting the set home and testing it I find it isn't actually switching off at all but its losing the back lights.

When the set is first turned on the back lights all light up and I read 12v going to them but then the voltage starts to rise and as soon as it hits 33v they cut out.

All pins from main to PSU read correct and are stable.

Any ideas anyone?

[tom66]

Re: LG 42LE4500 Losing Backlights

Where are you measuring the 12V increasing to 33v? Pictures would help.

[newtothis]

Re: LG 42LE4500 Losing Backlights

Phone is dead atm so will have to wait for pics... Im measuring these at the output of the PSU to the backlights

[newtothis]

Re: LG 42LE4500 Losing Backlights

the 12v to 33v was measured at the blue highlighted connectors.

the red highlighted area reads correctly and is stable

[tom66]

Re: LG 42LE4500 Losing Backlights

Those are the LED ones.
How long does it last?
Long enough to hook it up to a PC with a full white image -- you will be able to see if the panel is unevenly lit -- probably a dud LED.

[newtothis]

Re: LG 42LE4500 Losing Backlights

lasts 2 seconds, at first it was working for 2 minutes or their abouts. previous owner said it can take a couple of days sometimes for it to go.

no way to have time to hook it to my pc though, wouldnt get chance to change the input

first run on it and i went into menus etc... they take most of the screen and seemed even... but cannot be sure

[tom66]

Re: LG 42LE4500 Losing Backlights

Does it do the same with the LED strip connector unplugged?

[newtothis]

Re: LG 42LE4500 Losing Backlights

post back in 1 minute

[newtothis]

Re: LG 42LE4500 Losing Backlights

tried removing the led strips one at a time and powering on...

backlights switch off after 1 second instead

[newtothis]

Re: LG 42LE4500 Losing Backlights

WIth led strips plugged in... switch set on.. voltage rises to 12v... then climbs to 33v and switches the strips off.... the voltage then drops back to 12v and is stable.

with strips unplugged rises to 12v when set is switched on... drops briefly to 0v then back to 12v and is stable

[tom66]

Re: LG 42LE4500 Losing Backlights

Sounds like somehow you have a short in the LED strips.

[newtothis]

Re: LG 42LE4500 Losing Backlights

Checked via ohms down each of the strips and they don't read any signs of shorts.

I have just stripped down the panel and can confirm that all LEDs are lit at startup of teh set

[newtothis]

Re: LG 42LE4500 Losing Backlights

Tom to test if it is one of the LED strips could I unplug the strip one at a time and put a resistor in place to fool the protection circuit into thinking that it is connected?

If so what rating resistor would you suggest?

Thanks

[tom66]

Re: LG 42LE4500 Losing Backlights

Unfortunately you'd need a huge resistor, of the order of 25W, not really practical.

[newtothis]

Re: LG 42LE4500 Losing Backlights

OK on the pic is the controller for the LED strips... The connectors are to the right.

I have took reading down the board.

RED OUTLINED COMPONENTS FROM TOP TO BOTTOM :

PIN 1: .487K
PIN 2: 0K
PIN 3: .476K

PIN 1: .391K
PIN 2: 0K
PIN 3: .381Kv

PIN 1: .479K
PIN 2: 0K
PIN 3: .469K

PIN 1: .390K
PIN 2: 0K
PIN 3: .380K

PIN 1: .479K
PIN 2: 0K
PIN 3: .469K

PIN 1: .479K
PIN 2: 0K
PIN 3: .469K

PIN 1: .389K
PIN 2: 0K
PIN 3: .379K

PIN 1: .499K
PIN 2: 0K
PIN 3: .489K

1) YELLOW TOP TO BOTTOM
2) BLUE TOP TO BOTTOM

1) 1K
2) .476K

1) 1K
2) .380K

1) 1K
2) .468K

1) 1K
2) .379K

1) 1K
2) .468K

1) 1K
2) .468K

1) 1K
2) .378K

1) 1K
2) .489K

Yellow are marked - 102
Blue are marked - 474

[newtothis]

Re: LG 42LE4500 Losing Backlights

Tom do these readings look suspect?

[tom66]

Re: LG 42LE4500 Losing Backlights

I have no idea, I'm sorry.

[newtothis]

Re: LG 42LE4500 Losing Backlights

Could something before them in circuit change the readings of the resistors or is it a case of no matter if they are on circuit or out they should always read the same?

[tom66]

Re: LG 42LE4500 Losing Backlights

I'm maybe picking up a 37LE4500 today with a working backlight but dead T-con. I'll try to make some comparative measurements if I get it. Obviously, it won't be identical but should be similar.

[newtothis]

Re: LG 42LE4500 Losing Backlights

That would be awesome Tom.

Cheers