Solved! Laptop water spill, it works fine on external monitor, but no screen.

[Davi Rego]

Hi everyone,

I spilled some water 4 months ago on my laptop keyboard. It went off of course. I took it apart and dyed it up with Isopropyl alcohol, changed the thermal paste and cleaned the dust out of it. Made it fresh again. It worked fine, and even better then before (since now it had renewed cooling capability), but only on external monitor. The screen never came back from the tragedy.
I can see the backlight shining when it is supposed to, but there is no image. I wondered for a while if it could be something on one of the video cards, since it has an Intel 4600 and a Geforce GTX 850m, but both are working fine on ext. monitor.
Does anyone have any clue on what it could be?
I have some little experience on microelectronics, but I know nothing about laptop/motherboard video architecture. Is there some IC that controls the video that I've been missing? I searched for damaged ICs around the mb but found non. The video cable to the screen seems to be working fine too.

Any clue would be greatly appreciated.
Cheers

 

[webworkings]

I doubt it is the GPU since your external monitor works fine. However, it could easily be that the cable that connects the display became loose at either end. Or even got moisture in it.

Check the cable. Make sure it didn't get pinched, etc. when you were inside the laptop. If nothing there, then try carefully disconnecting it and then reconnecting it, at both ends, to see if that resolves the problem.

 

[Davi Rego]

I doubt it is the GPU since your external monitor works fine. However, it could easily be that the cable that connects the display became loose at either end. Or even got moisture in it.

Check the cable. Make sure it didn't get pinched, etc. when you were inside the laptop. If nothing there, then try carefully disconnecting it and then reconnecting it, at both ends, to see if that resolves the problem.

Yes! The cable! Thanks for the suggestion!
It was really a point that I had to double check and so I did since you mentioned it.
The pins of cable the are really really tiny, so it's hard to check conductivity them all, but I did check some of them and they were fine.
I was as careful as I could in reconnecting them back on their sockets
I guess I can kind of rule that out now.

I'm really worried that I'm missing an important IC here. I dont really now how the mb manages the information flow between VGA+Screen+Onboard Graphics+GeForce.

 

[webworkings]

Are you sure that the attached monitor and the external one are running on the same graphics? If they aren't, then it could be the GPU.

 

[Davi Rego]

Yeap. At least it's what windows 10 is telling me.
It's saying that they are both on the Intel(R) HD Graphics 4600
I also play some games using the GeForce.

 

[webworkings]

Short of the motherboard being the problem, I am at a loss.