Question Laptop not charging - Unable to identify the source of the problem

[dmaclean123]

I have tried the methods suggested on other threads and they didn't work.

The problem started when the DC jack came loose inside the laptop. All I had to do was glue it back in place, no soldering or anything else required. After I did this, the replacement charger I was using stopped working. The salesman in the shop said that it was because it was underpowering the laptop... it was BUT it also worked fine for 2 months, then happened to stop after I had been tinkering.

I then found a charger with the correct power stats and all seemed well. The battery charging light came on, and the computer powered up, but the charge never increased from 2%. I then thought it could just be the battery, because it definitely needed replacing (lasted 5 mins unplugged.) I plugged a replacement battery in and it was at 75%, but still never increased. What confused me more was when I simply took the new battery out and put straight back in, the battery level now read 2% again.

The laptop will power on without the battery plugged in. I have tried removing the battery and charger, and holding the power button in for 30 secs. I have tried uninstalling the battery drivers. The only thing I can think of now is that I might have damaged the DC jack when gluing it in, however, this seems unlikely as it's still powering the laptop and seemingly charging the battery (at least to the point where the indicator light comes on.)

Does anyone have any other suggestions as to what the source of the problem is and how I could fix this, please?

 

[stud858]

There is a section on the motherboard that handles charging and discharging of battery controlled by a power management chip. Possibly it is faulty or parts around it. Take a look at schematic if you can download it. Unfortunately you need more than basic knowledge. "Electronics repair school " on youtube helps a lot.

 

[dmaclean123]

Thanks for your response. I'm probably a bit out of my depth with that.. might be time for a new laptop.

Would that explain why the new battery went from 75% to 2% just through taking it out for a minute?

I did buy a replacement DC jack when I thought that was the problem. Do you think it's worth swapping out the old one, in case it's faulty, or is there no chance of that being the problem, based on what I've described?

edit: Another thing I forgot to mention (that could just be a coincidence) is that just before this happened, I had a virus and used Malwarebytes to remove it. It found a ton of dodgy files and I just binned them. I think this did affect some VSTs but possibly a few windows drivers that I had to reinstall. Could this have had anything to do with the charging problems?

 

[stud858]

I dont think dc jack has anything to do with your problem especially if you confirm inside the computer the pins on the mb show 19v OR the laptop works fine with battery removed.

The battery power management chip recieves data from the battery. You will notice the battery dock has more than two pins for just plus and neg. Some pins are for battery monitoring. Maybe the pins of the dock connector need resoldering or clean around the area with alcohol and toothbrush incl clean the pm battery ic. Other than that you need techy skills to continueon. Good luck champ

 

[dmaclean123]

Thanks again.

I wasn't able to find a schematic.
I've had a look at the motherboard and as far as I can see there's one obvious problem, which is a mosfet, between the DC in and battery, that's clearly burnt. See here:

https://drive.google.com/open?id=1-oR2P4TZAn1AcNW9iRrahs-i9upuAlzB

Is this most likely to be the only cause of the issue? If not, where could I learn more about how to diagnose it. I've watched a few videos from 'electronic repair school' but I'm struggling to follow without the basics. I'm hoping I can simply find a replacement and solder it it.. but is that just wishful thinking?

Cheers.

 

[stud858]

That MOSFETS does look stressed.
The only easy way to know for sure is a multimeter.
See a YouTube video how to test.
One side is 4 pins all shorted together.
Otherwise is 3 pins shorted together. And then the 4th lonely gate pin.
The 3 parts, gate, drain and source should not show short zero ohms.
But I think there will be more to it. The MOSFETs could even be ok.

Look for motherboard model and revision. It's written on one side of MB. Take a photo and post here.
I'll try and hunt down schematic so I can give you more help and pinpoint suspected component for your problem.
MOSFETs and smaller parts can be removed with two soldering iron method.
No need for special hot air equipment.
Not wishful thinking. Just a difficult repair.

 

[dmaclean123]

Awesome. Thank you, very much.

It's reading around 7.3, no matter how I test it.

It's not super clear from the first photo but I can see that the there is no contact on what I believe is the '4 pins shorter together' side. You might be able to see from this photo:
https://drive.google.com/open?id=1-rEMkHSYkI-6UBzEVctr-nLsAJYAitQe

The model is ASUS N551JM Main board Rev. 2.0

 

[stud858]

Sounds like that mosfet is buggered then.
now need to determine if a shorted part ahead of it made it go short. You'll be luck if that's the only issue. Possible though.
If you are sure one side of mosfet is shorted to the other then it will need to be replaced. Switch leads to test short both ways.
In the meantime give me a while to see if I can get schematic.a couple days max.

Could be that's a mosfet part of buck power supply that charges batt. It could have also taken out power management ic

All fun n games

 

[stud858]

Seems as though the best available is a short few pages that's not any use for this problem.
I recommend next step.
Remove suspect mosfet. To remove-
I oversolder each row of pins with heaps of leaded solder, then using two soldering irons sliding my irons around to melt everywhere. Then use irons like tweezers and move mosfet away.
Clean up area and check on pads to see if short is gone. Obtain new mosfet and solder. Don't forget orientation.
Try it out and smell if anythings burning. If not job well done.
Otherwise more fault finding. The power battery management ic is otherside of board
Getting the data sheet for that chip would help further if needed
Let me know how mosfet replacement goes.