No LED backlight - Asus Zenbook UX31E - poss burnt fuse after LED replace

Laptop MB Zenbook UX31E i5
No power to the LCD LED lights.

The Motherboard is Zenbook UX31E i5, 60-n8nmb4F00-b03.

I recently got this laptop Zenbook UX31E second hand.
I disassembled it to replace the LCD screen.

While attempting to reatach the LCD cable to the internal socket on the MB for the LCD display, when the 2 sockets were not completely positioned but still touching each other,
I heard a short cracking noise and I smelled burned.
After this moment the LCD would not power on!

I did the mistake of plugging sockets without detaching the battery!

HDMI to External display works and the laptop is functional with external display.
However the internal display does not work.

I found a burned SMD capacitor on the back side of the board.
MB back side.
http://s22.postimg.org/mcp7i01sh/20151219_210208.jpg

I got it replaced by a professional very carefully.

There is a small burn on 2 of the pins of the screen conector on the MB.
But I think it is not preventing them to send signal. The middle part of the pins looks not burned.
MB LCD Connector:
http://s14.postimg.org/9lk0544bl/201...34_resized.jpg
Front Side of the MB:
http://s7.postimg.org/ja4pj1b2j/2015...39_resized.jpg

After replacing the capacitor there is a almost completely dark image on the display. The data channel towards the LCD looks like its working now.
Back Side of MB with the replaced capacitor:

Front Side of MB near the LCD port wider view:


The LED lights that are supposed to brighten and light up the screen are not powering on.
There is a similar thread here in the forum, 50 pages about very similar problems, but it is about Sony laptops:
http://forum.notebookreview.com/threads/no-backlight-on-led-screen.613996/
Another one for Dell laptops:
http://forum.notebookreview.com/threads/inspiron-1545-led-screen-no-backlight.478489/

In these threads almost always the problem is burned fuse near the LCD connector, at the front or at the back of the MB.

Anyone has a circuit diagram for this board and/or help me find the burnt fuse?
Many thanks!

 

It could be the power circuitry itself for generating the right voltage and amps for the display.

 

If you have a multimeter; power up and verify the circuit away from and to the replaced capacitor. Flip the board; it continuous on the opposite side.

Yes, so either:

1. There's no power to the wled backlight.
2. The backlight-on pin doesn't connect/activate.
3. The fuse on the lcd has been triggered (if that one failed; the mb fuse, if any).

If you know which panel it is (sticker on the back), then it's possible to find out the purpose of each pin:

Spoiler: CPT CLAA133UA03 - pin configuration

There are no Asus diagrams, you'd need to look for the Compal, Quanta or Pegatron number (it should be on the mb somewhere). But even if you'd find one, they'd be utterly useless. Nothing on this board is labelled, save a few of the connectors. Without knowing what each smd does (or a clear 'N', 'T' or 'Z' on the smd itself, which is the fuses' rating), there's no way to repair it; capacitors and fuses can have the same form-factor/look, so you'd need a 'C***' and 'F***' to know which is which:

Spoiler: example mb - Clevo W230SS

Besides, the fuses will be found on the lcd itself, at the very least. Panels have different voltage/amp ratings and the fuse chosen will be specific to that panel. Good thing is that, unlike these throw-away motherboards, the lcd's pcb are usually (always?) labelled:

Spoiler: Samsung LTN173HT02-P01 - fuses

So check the lcd first, measuring the resistance of the fuses you find there. Only if these are all ok, then you might check all fuse-like SMDs on the motherboard itself. And clean both burned pins and the matching cable end; use contact cleaner and wipe dry.

 

Hello again,
and Happy New Year!!
t456, thank you for the detailed response.

Yes, the board has no any markings for the elements and there is no diagram.

- I am not really sure how to clean the display connectors.
I sprayed them with a contact spray (it is some form alcohol). I wiped them as much as I could. They are very gentle and not stable, so Im afraid I will tear them if I apply too much pressure.

I looked at the LCD but the elements are impossibly small for a bare eye.

Now here is the big news:
I got a replacement board which is almost identical.
I could compare the elements one by one between the 2 boards.
The new board has slightly weaker CPU (90% of the original).

With the new board I could try the LCD.

I would appreciate any advice how to measure the elements between the boards.
Including simple instructions. I do have a multimeter but I've used it rarely, only for simple tasks.
Also, how to minimize time and effort.

Thanks!

 

Fixed.
With the replacement motherboard my friend measured the burnt element and it appeared it is not a capacitor but inductor.
He replaced it again with one with the proper values and now the LED light works.

 

Good to hear, and kudos to your friend.

 

Hi. Do you have the correct part spec that needs to be replaced? I have the same problem. Or could i just solder both ends together (i did it on a dell and it worked)?