Asus ROG GL551JM doesn't charge after MOSFET failure

[KappaDev]

Hello, I have an ASUS ROG GL551JM laptop that recently died.
I took the motherboard out for a quick inspection and probed around to check power rails. On first checking I noticed the 19V main power rail was missing after the first MOSFET. The gate voltage was very low causing high resistance in the MOSFET and only allowing ~0.8V through the MOSFET source. I checked for possible shorts on this power rail but did not find anything suspicious. As a test I removed the MOSFET and shorted the source to the drain and the laptop appeared to power up fine. (I assume this is probably not recommended) However, now the battery would no longer charge. The battery itself is good and is detected with the percentage in Windows, but does not charge. The computer will also run off of the battery without AC adapter.

Looking at the boardview I am trying to piece together why this behavior is occurring and whether this is maybe due to missing voltage at the gate of the first MOSFET? (Since it's only source->drain short). Or perhaps a bad battery killed the charge IC which caused a problem in the first place.

I can take more measurements if needed.
The battery itself is outputting 10.5V and the laptop does power on with the required power rails 19V, 5V, 3.3V, etc.
I have attached the BoardView file (cannot be opened in OpenBoardView due to format but can be opened in BoardViewer).
I was unable to find any complete schematics online, but I did come across a diagram detailing the "power flow" and power-on sequence which I have also attached.

I would like to hear your thoughts.
Thank you very much!

[mcplslg123]

Re: Asus ROG GL551JM doesn't charge after MOSFET failure

this is maybe due to missing voltage at the gate of the first MOSFET?

Yes, you yourself has answered. Without the fet, you dont have correct voltage at the gate which in turn will disable charging. So just replace that mosfet and hopefully everything will be fine. Btw, this is the most commom failure on asus mb's.

[KappaDev]

Re: Asus ROG GL551JM doesn't charge after MOSFET failure

this is maybe due to missing voltage at the gate of the first MOSFET?

Yes, you yourself has answered. Without the fet, you dont have correct voltage at the gate which in turn will disable charging. So just replace that mosfet and hopefully everything will be fine. Btw, this is the most commom failure on asus mb's.

Thank you! I should also clarify that when I say "first MOSFET" I'm referring to the first MOSFET after the DC-in jack. I will try replacing it today.

[mcplslg123]

Re: Asus ROG GL551JM doesn't charge after MOSFET failure

Thank you! I should also clarify that when I say "first MOSFET" I'm referring to the first MOSFET after the DC-in jack. I will try replacing it today.

Thats well understood even without your clarification

[piernov]

Re: Asus ROG GL551JM doesn't charge after MOSFET failure

Usually it's the other MOSFET that shorts drain-source-gate. Second one in your case if it's the 1st one that doesn't let current flow through it.

[Gfelker]

Re: Asus ROG GL551JM doesn't charge after MOSFET failure

Were you successful in replacing the MOSFET and repairing the laptop? My GL551JM recently died and sounds very similar to your issue. Battery light started flashing and battery won't charge. Will discharge to 0 and shut off. Laptop won't power on using the AC adapter with the battery at 0 or with the battery removed. Looked at the motherboard or anything obvious (burnt components, loose connections etc). AC adapter is working (has voltage on volt meter) and tried a new battery.