LG 55le5400-UC AUSWLHR No backlight

[zyz]

Hi all,

This is my first post here, hopefully Im doing it right...
I found this tv, and have no background info on it, heres what it does.
I plug it in, touch the power button, theres a click, it radiates it's little lights, all the vol, menu, input, etc. touch sensors light up, the LG logo in center of bezel lights, and thats it, no backlight what so ever, not even flash for a second.No sound except for the when the buttons are touched, it gives a little feedback beep.

I took the back off, the power supply looks ok, (everything 'looks' new)
there is a little blue smd led on the driver board that blinks steady, and the green and yellow indicator lights on the ethernet port are dimly lit.

There is no 'stby' power spot to check for voltage, least not labled as such.
I checked voltages at power supply to main board...

ERR = 0
NC = 2.9
I-C = 0
P.DIM = 0
5x GND =GND
5X 24 = 24.5

There are some test points on the led driver, only getting 24v at the spot where it has the high voltage triangle, and 0v on all the others, im thinking thats a clue.

driver = 6917L-0025A
p/s = LG EAY60908801
mb = LG EBR66400202

About the pictures, do they need to be of my actual board, or would one from shopjimmy work, im not sure if i can get a good focused one, but ill see what I can do if thats what it takes

If anyone has any insight on this model, any help would be appreciated.
Not seeing alot of info on this model anywhere.
Its a project tv, just like to try and fix things, ive fixed several led displays, mostly cap replacements, and bad solder joints that worked well.

Looking forward to some kind of reply..https://www.badcaps.net/forum/images/smilies/lol.gif
Thanks

[martyparish]

Re: LG 55le5400-UC AUSWLHR No backlight

Do your best with pics of your own tv. Take one pic of the complete back of tv with all boards attached. Also closeup pics of each board.

The psu to main connector pins are labeled on the back of the board but even on the shopjimmy pics they are hard to read.

Also I see a "ONOFF" pin on the led driver as well as a surface mount fuse(white) that you can check.

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

Heres the pics.
Lemme try this again...
ONOFF reads 0v, im assuming the fuse is good since there is 24v south of it.

[CapLeaker]

Re: LG 55le5400-UC AUSWLHR No backlight

On the bottom right corner of the PSU is a pin out with voltages. Measure those and report back with pin out name and voltage tested.

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

Hi CapLeaker,
I guessing you mean top right, as the mains power comes in at bottom right of psu.

This is PSU to MB
pin:
1 PWon = 3.3
2= 24.5
3= 24.5
4= 24.5
5,6,7,8 =GND
9,10,11,12 = 3.4 (when front panel power switch is on or off)
13,14,15= GND
16 NC = 0
17= 12.2
18 DRV_on = 0
19= 12.2
20 P.DIM = 0
21= 12.2
22 NC = 2.9
23 NC = 0
24 ERR = 0


Not sure what that extra pinout above the 24 pinout means?
Trying these pics a few at a time.

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

Left connector on PSU to the LED DRV

pin
1,2,3,4,5 =24.5
6,7,8,9,10 = GND
11 P.DIM = 0
12 I-C = 0
13 NC = 2.9
14 ERR = 0

24.5v from pins 1~5 goes to the yellow cap, then down to the black trans.
Thats as far as I went, not knowing what to expect on the other side of the trans. (if thats even a transformer?)

[budm]

Re: LG 55le5400-UC AUSWLHR No backlight

18 DRV_on = 0
20 P.DIM = 0
No BL-ON , no Dimming control.

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

So I take it there should be some voltage at 18, DRV on?
Also, does the flashlight test work on edgelit panels?
I don't see anything in there, after trying to get the menu/input screen up.
I know what this looks like in smaller monitors.

Thanks for the help guys.

[CapLeaker]

Re: LG 55le5400-UC AUSWLHR No backlight

Yes, plus the dimming control.

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

So any ideas on what to check next?

[nicholas1110]

Re: LG 55le5400-UC AUSWLHR No backlight

I just had one of these in my shop last week. It was the main bga processor under the heat sink in the middle of the board. I reflowed the chip and tv works fine. There is also a few that offer this repair service on eBay as well incase your not comfortable doing it yourself. Hope this helps.

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

Hi nicholas1110

Is there a way to confirm that this is my problem?
Im armed with a DMM and a soldering iron

I've reflowed the MB of an HP dv7 (using it right now) laptop I found, not sure you'd approve but I did it the redneck way... in the kitchen oven.
Also heated the graphics chip in another HP dv? with a heat gun, that worked, but not for long, plan is to try that one in the oven one day.

anyone know how to get the led's to light, basically to see if the screen is cracked. Like I mentioned, I have no history of this set, and dont wanna mess around to much on a hopeless case.

[CapLeaker]

Re: LG 55le5400-UC AUSWLHR No backlight

can you get any sound out? check the LVDS with an oscilloscope.

to force on the PSU you need two 1k ohms resistors. Remove the main board from the power supply. One resistor goes between STBY voltage and PSon, the other from STBY voltage to BLon. Plug it in and the lights shall shine!

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

Thanks CapLeaker,

No sound, and I dont have an oscilloscope.
Is this to check the main bga processor, as nicholas1110 suggested?

Referring back to post 5, and 6, which exactly is my STBY, PSon and BLon. ?

[CapLeaker]

Re: LG 55le5400-UC AUSWLHR No backlight

PWon = PSon
DRVon = BLon
and you may have to do the same thing to the PDIM.
The oscilloscope on the LVDS trick is to see if there is video coming out of the main board, to rule out the TCon for sure.

[mmartell]

Re: LG 55le5400-UC AUSWLHR No backlight

If you suspect a bga chip you can thoroughly heat it with a hair dryer to see if your symptoms change.

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

I removed the heat sink from the main processor, put some hair dryer heat on it, and viola, it sparked right up(no cracked screen either).

The touch buttons didn't do anything, but a hard reboot fixed that.

So, did heating it do something to the solder connection?
(I dont think it got hot enough for that)
Or did it just do some stretching of circuits inside the chip somehow,
and will go back once it cools.

Would anyone suggest baking it in the oven?
When I did that to the dv7 mobo, I put a small piece of solder on the copper thats showing around the mounting hole, set oven for 428f and waited for the solder to melt.

CapLeaker, thanks for the details on the pinouts, I was thinking the same as you described, haha, the one that I really didnt know was the stby... Im assuming stby is always the one that is constantly energized?
I thought stby was always 5v, is 3.4v a common value also?
Im thinking that would be spec'd at 3.5v

Thanks everybody for the suggestions.

[CapLeaker]

Re: LG 55le5400-UC AUSWLHR No backlight

STBY voltage is always on, regardless... as long as the power supply is plugged in. STBY voltage itself can vary. Most have 5V, but there can be also 3.3V ones too, your is 3.5V.
PSon comes from the main board and it needs to be higher than 2v. That signal actually turns all the voltage rails on the power supply fully on.

[mmartell]

Re: LG 55le5400-UC AUSWLHR No backlight

You did a temporary stretch so it's likely to fail again. If you feel confident baking it give it a shot.

[zyz]

Re: LG 55le5400-UC AUSWLHR No backlight

Update and question:


It has been working ok so far, except for now and then when changing anything , the OSD sometimes goes crazy and randomly moves through settings, while its doing this the touch panel does not respond. Needs to be unplugged, or sometimes, only the power button on the universal remote works.

I will bake the mainboard when it stops working.

also the hdmi inputs do not work, read online this is a common problem that baking often remedies.

How do I get into service mode on this?
I tried the OK remote/OK panel... Menu remote/Menu panel method, that did not work, I do NOT have an OEM remote if that matters.