Hi everybody,

I recently bought a chinese universal power supply for my laptop with different plug adaptors and unfortunately the one I used had polarity marked in reverse. Long story short, I fried something.

Fortunately my laptop (Asus x551c) still works perfectly on battery alone, but when plugged (correctly) the system says it's connected to AC and charging, but actually it is not and my battery keeps discharging until dead. Now my laptop won't turn on as my battery died and if I remove it and use just the power supply it does nothing at all.

I made a few tests, power supply does work perfectly since I use it with other computers too. When connected to the faulty laptop, it draws just 1,4 milliamps instead of 2,37 amps as it should. I opened the laptop up and didn't find any fuse or dead components, so I checked with a tester and found that right after the positive pole of the plug there is an IC called M3024M whit 8 pins, 4 of which are connected to the positive pole, 3 to the rest of the circuit and one of them to an smd component that I can't recognize. I couldn't find any datasheet on the internet, but this component should be a mosfet protection circuit since there is an identical one after it placed in reverse, and I've already seen similar topologies elsewhere. It causes a huge voltage drop, from 19V input to less than 1V output when AC is connected, but no drop at all when there is a battery.

Can anyone give me some infos about that M3024M? May that be the faulty one or should I check something else? Do you know any substitute?

Thanks in advance!

 

Ok I've checked further more and figured out the whole system is based on a BQ25A microcontroller that drives 5/6 mosfet in order to switch from AC adapter to battery. According to its datasheet there should be a third mosfet at the input to manage a reverse polarity, but my laptop seems to not have it, or at least I didn't find it. I don't know if the mcu has been fried because of this missing protection, but since battery charge is recognised correctly I guess it's all right. The problem may still be at the first mosfet for what I can tell.
Any suggestions?

 

hi MS,
This link shows a M3024M.
http://www.ebay.co.uk/itm/1-x-QM302...378429?hash=item25d05a727d:g:bhkAAOSwOgdYsckS

E

 

Thanks @ericgibbs but unfortunately there's no datasheet there. Anyway, since I realized it is just a mosfet, now I need to know how to check if it works right with the BQ24725A, anyone has any clue?

 

It is just an NMOS transistor, and without protection circuit this is likely toast. To find datasheet add Q as prefix when searching... QM3024M

 

I found it!!! Never thought a Q could make such a huge difference

Thanks a lot panic mode!

So you think that's the one I fried more than the mcu?

 

this circuit only has a handful of components. not sure where your comfort and skill lies but replacing high power components (transistors) is a simple thing to try. one can of course test them too...

 

UPDATE

After various months without touching this computer, I finally decided to repair it. Since I don't have any SMD soldering tools, after many attempts I discarded the idea of a replacement and quickly jumped the broken part of the circuit bypassing the two faulty mosfets. Now my laptop is working again (I'm writing from it right now) but the battery is not detected even thought the charging led is on. Maybe it is dead since I left it uncharged for all these months or maybe that's because the jumper doesn't allow the system to switch from AC to the battery. I don't know, I have to check further. But since I'm leaving it plugged to the AC anyway it's not a big deal... Thanks all for the help!

 

UPDATE

After various months without touching this computer, I finally decided to repair it. Since I don't have any SMD soldering tools, after many attempts I discarded the idea of a replacement and quickly jumped the broken part of the circuit bypassing the two faulty mosfets. Now my laptop is working again (I'm writing from it right now) but the battery is not detected even thought the charging led is on. Maybe it is dead since I left it uncharged for all these months or maybe that's because the jumper doesn't allow the system to switch from AC to the battery. I don't know, I have to check further. But since I'm leaving it plugged to the AC anyway it's not a big deal... Thanks all for the help!View attachment 143436

Hello Michele

Did you finally found a way to replace mosfets to have it charging again ? Or left as is after your "fix"?? Slso how did you find the correct place to the bypass location?