Asus UX31E missing backlight after replacing LCD

[Tomppa]

Hi there,

Bumped to a typical (stupid) problem while replacing LCD panel in my laptop...
Didn't remember to disconnect battery before the job and now I have a laptop with functional LCD without backlight. Patient is UX31E from Asus.
I know there has been similar problems with other Asus models, but couldn't find fix for this model.
Anybody have a clue what components to check (couldn't find any schemas/layout)?
Any help appreciated!

[atsio]

Re: Asus UX31E missing backlight after replacing LCD

For the schematic look at this post.
https://www.badcaps.net/forum/showthread.php?t=44464

Check voltage on pins 11,13, and 14 of lvds connector.
Also check voltage on pins 1,2,4 and 5 of U4501

[Tomppa]

Re: Asus UX31E missing backlight after replacing LCD

Thanks atsio. Will do that.
Schematic seems to be for UX31A, hopefully it's the same from LCD backlight perspective. Any idea where this U4501 is located?

[senso]

Re: Asus UX31E missing backlight after replacing LCD

Around the LVDS connector there should be one or two mosfets with 15-19v at the source if I'm not mistaken, usually those are the mosfets that "blow" and so your panel has no power for the backlight, they are usually in SOT-23 packages, there was some HP model that I have changed a couple of the mosfets and a bulk decoupling cap, a 0805 10uF cap.

[atsio]

Re: Asus UX31E missing backlight after replacing LCD

Any idea where this U4501 is located?

Five pins (3 one side, 2 the other) with marking VE on top. Check for continuity of pin 4 with pin 14 on lvds connector to confirm.

[alextheonly]

Re: Asus UX31E missing backlight after replacing LCD

I am currently facing a similar issue with the backlight on my Asus X750LA. I am aware that the models are different, but after researching hundreds of threads I cannot locate any fuses or failed caps around the LVDS connector on the motherboard. Upon discovering this thread, I'm curious if I should be checking MOSFETs and the U4501 chip if my motherboard has such a chip?

[Tomppa]

Re: Asus UX31E missing backlight after replacing LCD

Ok. Finally got the time to check the main board...
Found out that the ferrite L4518 at the +3VS_LCD line was burned. Replaced it and everything works again. No other damages found.

[dacianhorja]

Re: Asus UX31E missing backlight after replacing LCD

Ok. Finally got the time to check the main board...
Found out that the ferrite L4518 at the +3VS_LCD line was burned. Replaced it and everything works again. No other damages found.

Hi, i have the same problem as you, no backlight after screen replacement.
Could you post a picture of L4518 to see where is located?

What if I can not find a replacement? Can I just short circuit the burned one?

Thanks!

[Tomppa]

Re: Asus UX31E missing backlight after replacing LCD

Hi. Already sent you a private message, but here's the explanation where to find the L4518.
Remove motherboard from laptop chassis. Find TOP side of motherboard (should be marked on PCB near USB connector).
L4518 (together with another component) is located between the USB connector and screw hole near USB conn. L4518 is the closest one to the screw hole.

[dacianhorja]

Re: Asus UX31E missing backlight after replacing LCD

Hi. Already sent you a private message, but here's the explanation where to find the L4518.
Remove motherboard from laptop chassis. Find TOP side of motherboard (should be marked on PCB near USB connector).
L4518 (together with another component) is located between the USB connector and screw hole near USB conn. L4518 is the closest one to the screw hole.

Hi Tomppa.

Thank you for the picture/ help.
It was exactly that piece that made my screen not light up after screen replacement.

I did not had a replacing part I just replaced it with a piece of wire.

Now light are on again!

Thank's!

[schix999]

Re: Asus UX31E missing backlight after replacing LCD

Hi guys, I have the same issue with my UX31e (lcd backlight). Where do I buy the part and how would I go about replacing it? I was planning to get this fixed but the Asus repair centre quoted around 500 for the lcd replacement. I'd be better off buying a new laptop however, I'd like to see if I can fix the backlight issue. So please help me out. Thank you.

[Dava]

Re: Asus UX31E missing backlight after replacing LCD

Thanks for this guys. I had exactly the same issue, removed display before removing battery and fried this ferrite. I linked it and all is now fine again.

What are the implictions of removing and linking, will it just just affect EMC or should I try to replace with the correct component?

[Th3_uN1Qu3]

Re: Asus UX31E missing backlight after replacing LCD

It will make that supply a little more noisy. If your LCD panel isn't bothered by it, leave it jumpered and be happy.

[Djosla]

Re: Asus UX31E missing backlight after replacing LCD

try to replace with exact component,if for anything else it is there for protection from this things...emc is not a big deal here...

[jaymills1111]

Re: Asus UX31E missing backlight after replacing LCD

I can't seem to make anything work, I have located the broken ferrite but I don't have a soldering kit or the replacement part, how would I go about shorting it?

[Wideback]

Re: Asus UX31E missing backlight after replacing LCD

Hi Guys,

I don't mean to be a thread hijacker but this is the closest information i've been able to find on the issue i've got. Alright so I have an ASUS S55LB and like the OP i've just replaced the LCD and made the ol 'forgot about the battery connector' mistake. This is a touchscreen model and if I look at the screen with a light I can still see the data faintly and the touchscreen is still functional but of course...no backlight, I can confirm it was working beforehand.

I've had the mobo out and the only thing that I noticed that was strange was a resistor marked 0 that was a little out of place and had no continuity. I've since taken this part off and put a bit of solder to link back up, it now has continuity but still no backlight! (I am aware it's not the best solder job so i'm not ruling this out)

I've taken a few pics of the top and bottom sides of the mobo around the LVDS connector area in the hope that someone might be kind enough to have a quick look and see if im missing something. There are a few parts that i'm not 100% sure of and they dont seemed to be marked so i've circled one on each side...are these fuses? Any help would be much appreciated!

Cheers!

[Cams]

Re: Asus UX31E missing backlight after replacing LCD

Hi. Already sent you a private message, but here's the explanation where to find the L4518.
Remove motherboard from laptop chassis. Find TOP side of motherboard (should be marked on PCB near USB connector).
L4518 (together with another component) is located between the USB connector and screw hole near USB conn. L4518 is the closest one to the screw hole.

I have exactly this problem with the UX31E. I didn't know that I should detach the battery. Is this an easy job? I've never soldered before, but I do have a soldering gun in a drawer. Are there some instructions somewhere?

[dinsdale79]

Re: Asus UX31E missing backlight after replacing LCD

Hi, I aslo have same problem with ux31a. A friend of mine replaced a faulty power jack for me. After that while assembling the laptop I connected the LCD strip with the battery plugged in. I've heard some cracking noise and now backlight is gone.
I showed the laptop to two different "laptop repair specialists", but it turned out they're not really that good. One told me that there's something wrong with the motherboard, but he doesnt know what (he checked all the fuses he said). The other said the led backlight is faulty and I have to replace the whole upper lid.
Is damaged baclight itself possible in my case? Or it's rather the motherboard?
Another interesting thing is that the laptop doesnt do anything after I close the lid, eventhough I set up in win10 that it should hibernate after lid closing. So it got my suspicious about the reed sensor. But the keyboard is working fine. Faulty reed sensor would block backlight and the keyboard, right?
Also I can't power up the laptop normally. Every time after shut down I have to disconnect the battery, reconnect it and then plug in the ac adapter, then it starts automatically without even pressing the power button.
Befor that unfortunate laptop assembly everything was working fine.

LVDS readings:
pin 11: 19V
pins 13 and 14: 0V
pins 18,19,20: 3.3V
I can't locate U4501.

Any help would be greatly appreciated.

[mielta]

Re: Asus UX31E missing backlight after replacing LCD

Hi
At the top side of the Board JP3001 alittle deeper is a 5pin Chip
that is U4501
At the hole H6510 there are two smd components you must check the impedance from the left is must be 120Ohm.

[dinsdale79]

Re: Asus UX31E missing backlight after replacing LCD

Hi
At the top side of the Board JP3001 alittle deeper is a 5pin Chip
that is U4501

Hi, thank you for your reply.
I think I located the u4501. I marked it on the photo. Is that the one?


Pins 1,2,3,4 show 0V. Pin 5: 3.3V

At the hole H6510 there are two smd components you must check the impedance from the left is must be 120Ohm.

Last time I just checked the continuuity (it was fine). I'll check the impedance tomorrow.