T540p no backlight (but there is picture)

[abgersaurus]

Hi guys!

I'm really having a bad time, my laptop is currently unusable since the backlight is not working on either the TN panel or IPS panel that I have for it.

when I first got the laptop it worked fine, allthough it ran a bit hot 65c idle. So I decided to change the thermal paste for with some Arctic Silver MX-4 and the idle temps dropped to 43c idle, a very nice improvement if you ask me.

Then I decided to change the awful TN panel that it came with since I've done that a thousand times before with other laptops, so I went ahead and ordered one from eBay (it came from UK) since I did not want to risk some china panel potentially breaking my precious new laptop.

when I got the new panel, I turned off the laptop then removed the battery and pressed the power button for 30 seconds, then porceeded to take the bezel off and remove the "old" working display and install the new display. No problem.... or so i thought...

There was only a black screen when i booted it back up!
turns out that the backlight was not working (I was shining with a flashlight and getting a picture on the monitor itself)
I then did the same procedure and replaced the "new" monitor(IPS) with the "old"(TN)

still no backlight... I really needed it for my school, so I went to a local PC-repair shop that could fix things such as laptop.

thay said that there was 3 possibilities:
broken monitor
broken motherboard (GPU is soldered on motherboard)
borken cable from motherboard to the monitor

they could NOT fix my laptop sadly and I decided to try myself and finally got a new cable from eBay which sadly did not help, here I'm just sitting with a laptop that has 2 monitors a TN and an IPS panel no backlight in either of them.

Does anyone have a solution?

(I've tried installing, fingerprint driver, displaydriver (lenovo,Intel & Nvidia) and replacing the cable from the motherboard to monitor)

PS I spoke to a guy from lenovo support who said that the onsite guaranty is gone due to me changing the thermal paste.

I can upload pictures if it helps!
edit: is something missing here? https://gyazo.com/9d4695779e7e6bca53a9da319b59bfe5

[RealBlackStuff]

Welcome to the Forum.

Most likely you've blown a fuse.
Check for fuses around the LCD-cable connector on the motherboard.
They are usually indicated with F1, F2, F3 etc. printed nearby.
Measure them with a multimeter, set to Continuity/Beep.
If you can, replace it, otherwise piggyback solder another one on top of it.

[abgersaurus]

Welcome to the Forum.

Most likely you've blown a fuse.
Check for fuses around the LCD-cable connector on the motherboard.
They are usually indicated with F1, F2, F3 etc. printed nearby.
Measure them with a multimeter, set to Continuity/Beep.
If you can, replace it, otherwise piggyback solder another one on top of it.

wow! thank you so much for the fast reply, i'm not an expert at soldering so i might be a bit hard, also can it be seen from this photo?
https://gyazo.com/3ac3d4d2cb6973688c8e39fc2a9e6cbf

[RealBlackStuff]

On the pic I can see F11 (left of connector), but you'll have to take the motherboard out to get at it.
I don't have the schematics, so I can't check.

[nitrocaster]

Those green components with 'O' mark are fuses. Check them with multimeter.

[RealBlackStuff]

No, they are not.
This is what a fuse looks like:

Also, about 2/3 from the left, along the bottom I spotted an F4 marking.

[abgersaurus]

Thank you guys, I did however start to take it all apart before I saw your suggestions, and by testing EVERY single fuse with the "F" mark I finally concluded that the "F11-Fuse" is defective as there is no Continuity/Beep. I therefore plan on contacting my local pc repair shop for some assistance since I'm unable to solder/replace it myself here are some picture of the fuse that I need to get replaced and every other single fuse I could find

These pictures might just come in handy for somebody else in the future, I am going to take some more hi-res pics soon

https://i.gyazo.com/79a7bf0d13a78133ccd ... caabf3.jpg F11 Fuse (monitor)

rest of the album
http://imgur.com/a/i6lCz

[RealBlackStuff]

I repeat: those F4 and F11 thingies (green with a white O) that you marked are NOT fuses!
They are most likely zero-Ohm links.

[abgersaurus]

I repeat: those F4 and F11 thingies (green with a white O) that you marked are NOT fuses!
They are most likely zero-Ohm links.

ok, can you see the actual fuses then? that would be much appreciated

and howcome the F11 green thingy with the 0 does not beep as the F4 does?

[RealBlackStuff]

Sorry, I can't.

[abgersaurus]

but the green thingy looks just like the "fuse" that you showed earlier but just with an 0 instead of N

[RealBlackStuff]

Fuses don't have metal sides/borders along the (long) sides, there's only metal at both ends where they are soldered.

Someone commented on your Imgur pictures:

notfiringonallthrusters1 pt 1h
what you have circle are capacitors and zero ohm resistors, more like jumpers than fuses, they would only blow as a last resort

[abgersaurus]

oh ok, I guess I'll just have to ask around a bit to be sure before I do something stupid!

[abgersaurus]

is it still possible though that one of the so called capacitors might have to be replaced? my monitor stopped working when I swapped it and then the backlight did not work anymore?

the guy wrote that they would only blow as a last resort, which might be the case...

[nitrocaster]

I repeat: those F4 and F11 thingies (green with a white O) that you marked are NOT fuses!
They are most likely zero-Ohm links.

These are fuses. 'O' encodes 2.5A rating.

[nitrocaster]

is it still possible though that one of the so called capacitors might have to be replaced? my monitor stopped working when I swapped it and then the backlight did not work anymore?

the guy wrote that they would only blow as a last resort, which might be the case...

Connect LCD panel to the motherboard and check if the top pad of F11 is shorted to ground (diode mode, red probe on ground, black probe on the point of interest).
If there's no short, you just need to replace F11 fuse with compatible one (2.5A, 30-35V).