Diagnosing/repairing a Laptop motherboard?

Thread Starter

killsec

Joined Apr 13, 2020
5
Hey guys! First time posting here! I have an Alienware 17 R3 laptop that I picked up broken to see if it was repairable (I like learning new skills). All signs point to a short on the motherboard, I plugged in the charger and the blue LED on the charger cable goes out immediately if I attempt to plug it in and I got some magic smoke from the charger port. I have a new port on the way, but I disconnected the port from the motherboard (It's socketed) and plugged in the charger and no shorts occurred and the LED stayed on.

So moving on doing some preliminary research I found that capacitors are the most likely to cause this issue so I started to dig around the circuit near the battery and charger connection. Now, I'm still learning about component troubleshooting, I'm very beginner at this point, but I found an 0603 ceramic cap that has continuity through it where the 3 others near it do not. I have been told some contradictory information from various experts and wanted to get general consensus on this. I know the only real way to test components is to remove them from the circuit and test individually, but I figured I'd start looking for the oddball before removing. This particular cap behaves differently from the rest when probed. Am I right in assuming there is a potential issue here? I have an air reworking station and all the know-how to remove and reinstall the components even of this size, I just need help with the identification of what needs swapped. Anyone want to help take a crack at this?
 

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AlbertHall

Joined Jun 4, 2014
9,875
When you measure components in circuit then the other things connected may distort the readings.
In my experience such capacitors may go open (perhaps being cracked) but rarely short). In this case there may be a low resistance path across the capacitor or the capacitor may be short circuit. Without a schematic, the only way to tell is to remove it from the board.
 

Thread Starter

killsec

Joined Apr 13, 2020
5
So I completely removed the motherboard from the casing and found a suspicious discoloring. Pictures attached are from same spot, both sides of board. If you saw this, what would be the first thing you'd start looking at? It looks like multiple parts might have been burned possibly.
 

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AlbertHall

Joined Jun 4, 2014
9,875
I can't see what you mean in the pictures. The USB connector looks quite corroded though so it may be some liquid was spilt into the laptop.
 

Thread Starter

killsec

Joined Apr 13, 2020
5
QV92, UV3 on the first picture looks like those components among a few others are a little bubbled. It does look like it could've been corroded though. I'm going to take some isopropyl to the area and see if it can get cleaned up, but there's no way I could be getting a short for just that is there. Also, that is the HDMI port.
 

AlbertHall

Joined Jun 4, 2014
9,875
If it has been wet then electrolysis takes some metal ions into solution and then when the water evaporates can leave a conducting path across the board.
You could give a good brushing with washing up liquid (US dish soap) first, then the IPA.

And then I found this too! I picked a really good board to learn on. :D
You don't need to remove that one to know that it is faulty!
 

Thread Starter

killsec

Joined Apr 13, 2020
5
Never heard of the dish soap but I'll give it a good cleaning. As for the component that is clearly bad, what steps can I take to identify it? I can rework it, I just need to know what to look for to order up a new one. Also, do you think this is a smoking gun? That is, I can replace that piece but is it likely something is causing it to blow? I don't know anything about the previous owner, so maybe it was water damaged and I guess that could've possible led to a failure.
 
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