LG 47LN5400 Problems

[offroadz]

Just going to start off by saying I'm new to the forum, I'm here unfortunately due to an issue with my 47" LG TV. So this problem started about 2 months ago, where the image would looking like it was getting distorted with random lines with a greenish coloring. This would sometimes then lead to the TV being unresponsive at a white screen where only unplugging it for a few minutes would allow it to be useable again. I'm going to try to get a picture of what its doing I just never think of it due to me getting angry. Thanks for any help, I have never worked on TV's before so this is going to be a learning experience.

[alfonsoreyesd]

Re: LG 47LN5400 Problems

i have the same tv lg 47ln5400 screen dont light up,, tv powers on i check all voltages from power suppy to the main board and everything looks right,,, my main concern is voltages from the power supply to the screen,, just in case i replaced 3 high voltage caps but still the same,,, anybody know the right voltages on connector p801 my measures are
led - 32v
led + 79v
led - 7.8v
led + 77v

[budm]

Re: LG 47LN5400 Problems

i have the same tv lg 47ln5400 screen dont light up,, tv powers on i check all voltages from power suppy to the main board and everything looks right,,, my main concern is voltages from the power supply to the screen,, just in case i replaced 3 high voltage caps but still the same,,, anybody know the right voltages on connector p801 my measures are
led - 32v
led + 79v
led - 7.8v
led + 77v

We need good clear pictures of your boards.

[alfonsoreyesd]

Re: LG 47LN5400 Problems

[budm]

Re: LG 47LN5400 Problems

So you replaced those 4 caps by the LED connector, what DCV do you get measured right at the two legs of each when the TV is turned on each times? You have to measure one cap when TV is first turned on, then turn off the TV and move on to the next cap and measure the DCV, do that for all 4 caps.
Is this the exact matched of your board?
http://www.shopjimmy.com/lg-eay62810...upply-unit.htm
Provided by ShopJimmy

[Alastair E]

Re: LG 47LN5400 Problems

LED Driver board on PSU Faulty....

Common issue with LG sets....

Unfortunately the schematics are not available either for the PSU or the LED Driver, and neither is the LED Driver available separately, so you'll be looking at replacing the whole PSU
--Or modify the set to do away with that troublesome idiot LED Driver board!

See this thread where I did just that on a similar model--

https://www.badcaps.net/forum/showth...light=42le4500

Edit--Looks like you have a all-in-one PSU board without the sub-board, so implementing any modifications will be much more difficult....

[alfonsoreyesd]

Re: LG 47LN5400 Problems

yes is exactly same board im working on,,, voltagages of 4 capacitors right next to connector are 77v each either tv on or off,,, thanks for quick answers

[alfonsoreyesd]

Re: LG 47LN5400 Problems

i bought a used power supply board even everything looks right because i found it cheap like $24.00 so at this point i think is gonna be the logic board grrrr....

[Alastair E]

Re: LG 47LN5400 Problems

i bought a used power supply board even everything looks right because i found it cheap like $24.00 so at this point i think is gonna be the logic board grrrr....

If you have no backlight/LED's lighting then its Unlikely to be T-Con board--Possible--but very unlikely.

Usual culprit is the LED Supply. It has a controller that drives the two strings of LED's.
The + connections of the LED strings are both connected to the LED main supply rail generated by the PSU.

The Earthy end (-) is then connected to the controller transistors, where its PWM controlled for brightness, hence you see the two neg leads of the LED's at different voltages The LED strings (On a 42" set) need at least 65V Across the string to produce ANY light, so I'll guess a 47" set will need a couple of volts more....
Average running volts for a 42" I did recently was 83V, so guess your 47 will probably need say--89-95V average to give reasonable brightness picture.

Often the controller chip itself fails--and its a bit of an oddball--at least the one I had was....
--When the control-chip aint happy/faulty/fault detect, it will generate 'ERR' voltage, the main PSU then will go into 'low output' and supply 72V--Enough to make the circuit work and give a very low light on the LED's--but only if all is well--It will shut down completely after a short time.
--With fault condition, there's no light from LED's at all, even when the low-volts is present

[tom66]

Re: LG 47LN5400 Problems

There's unfortunately no general rule on how many volts per inch - because manufacturers can use different LEDs and different levels of current to reach the required brightness. A 32" Vestel set I fixed recently used 57V; a 22" used 35V... and yet my 24" monitor had a single 100V strip...

The cathode end of the strips is balanced using a current regulator (PWM also used) to keep the current between each strip within some matched limit so the brightness is (relatively) even between strips.

If you have the panel sticker number, e.g. "LG Display LC47WXN"... I might have a datasheet with voltage/current specs.

[alfonsoreyesd]

Re: LG 47LN5400 Problems

anybody has the diagram or troubleshoot manual,, because i orderded the board and same thing,,, i will have to return it

[johnboy1313]

Re: LG 47LN5400 Problems

Can you measure the voltage across the legs of the big main capacitor when the set is off and when it's "on".

[alfonsoreyesd]

Re: LG 47LN5400 Problems

big fat capacitor voltage when is on is 397 VDC when is off keep going down from 397 VDC to 172 VDC

[JeffJ]

Re: LG 47LN5400 Problems

alfonsoreyesd,

I just repaired a 47LN5750 which has the exact same Power board and led system as yours. with the same issue and the same voltage drops.

It was a bad LED strip. I replaced it and the tv fired up perfect. I tried the PSU first and that was not it. If you pull the panel out you will find a led strip that looks a little blackened on one of the leds. probably in the L1 bank as it seems common.

[alfonsoreyesd]

Re: LG 47LN5400 Problems

i will open the panel....... ADVICE !!,, testing component by components one by one i found D251 draw on the board upside down, ( on the board draw says pins 1 and 3 are cathode and pin 2 anode,,but pins 1 and 3 are anodes and pin 2 is the cathode)

[budm]

Re: LG 47LN5400 Problems



Silscreen mistake or some one put in the wrong Diode, but looking at the bottom side, that diode should be common Cathode so the part is correct but the silkscreen is wrong.

[alfonsoreyesd]

Re: LG 47LN5400 Problems

i opened the panel and yes l1 and r1 strips are kind of dusty and looks like overheated ,, but how do i test them,, if are only diodes (leds) i shouldnt have any problem test them but if i use ohms or diode any strip i test looks like open circuit

[JeffJ]

Re: LG 47LN5400 Problems

Can you post pictures. In my case when the L1 strip was bad in one of the L1/L2 banks one of the diodes had a distinct yellow/brown burn mark inside of it and looked different then the others. i was able to identify it with out even testing. However i moved the strips in the bad bank to the bank that was lighting momentarily to test the rest of them.

But you can power the tv with out the panel in it the back-lights should flicker on for a couple of seconds and you will be able to identify the bank with the offending strip in it. If your getting no back lights at all that means both banks of 4 strips has a bad led(s) in it.

Visually you will be able to identify them as its quite clear what one has shorted. As for them being dusty there should be no dust in there. What you are seeing cannot be dust unless some one has opened and left that unit open before exposing the screen innards and what not. the chassis diffuser and panel seal that off pretty well.

Since they are in series 1 bad strip will shut down all 4 strips in the bank.

[alfonsoreyesd]

Re: LG 47LN5400 Problems

i was able to test L bank,, using 12v external power supply,,i found 2 dead leds on 2 different strips,, however i cannot test the same way R bank,,, any ideas

if you see the X means dead led,,, some of the pics shows either dust or overheat

[alfonsoreyesd]

Re: LG 47LN5400 Problems

here are the pics