[FIXED] ASUS N550LF Notebook Motherboard - Power management problem

[Watth]

For my N550LF laptop, I have a compatible power brick. This power brick comes with a set of bits to fit the different brands. There is a fool proof poka-yoke top prevent mismatching polarities. The thing is now the adaptor bit would detach from the cable that comes from the power brick, and stay plugged into the PC. So I regularly have to plug back the cable to the bit.
Last time the bit disconnected, I inadvertently put i backward, the leads made contact on the wrong polarity.
Symptoms : the PC could restart, the power light was orange meaning power came from the power brick and was charging. Actually it was powered by the battery. I did'nt think of checking the power icon in the tray bar... So that the PC went off when the battery was fully discharged.
(I tested the AC adapter : it still delivers 19V).

When I tried to boot it again, it only lasted for a few second, only running on the few energy remaining in the battery.

I tried booting with the disconnected battery: nope.
I tried unplugging both power brick and battery, and pressing the power button for a few dozen seconds, then plug in only the the AC adapter. Nope.
I tried the same having removed the RAM and back-up battery: nothing.

I took out the motherboard to see if there was any sign of magic smoke, but I couldn't find any. Note : I am not an expert so mayyy beee I missed something, but it doesn't seem to be the problem.

The motherboard is N550LF Rev. 2.1; part number 60NB0230-MBA020(216).

Here are pics of my actual motherboard:
Front: https://www.flickr.com/photos/matthieurouy/27902531025/ (I mis-framed this one :/ , if needed I'll take another photo)
Back: https://www.flickr.com/photos/matthieurouy/27867463386/
"Front" an "back" respectively front and bottom orientation of the board when installed in the PC.
In flickr you can download the image in its original size for more details
If needed, I'll be glad to take other pictures!

DC In socket is top-left of the front picture; top-right on the back one.
The battery connects to the black connector on the lower edge; in the 'back' picture picture it's the black connector stamped "14160". You can partly read the reference "PJ6001".

I don't know where to start. What component I should I test, knowing I only have a pair of multimeters.
A new motherboard would be at least 200€ (for a used one, maybe of an older rev.). The electronic repair shops around where I live are sparced, and I doubt they'd do more than suggest to change the whole board.

Any idea?

TLDR: A N550LF rev. 2.1 motherboard will only work on battery until depleted. I need to fix the power management part that deals with the DC in stuff.

Thanks a lot for you attention!

[Watth]

I found some docs. these are regarding the previous rev (2.0) but that might still be helpful:
https://drive.google.com/folderview?id=0Bxw9rfoZdSfFVWN6c0FiYW4xZnc&usp=sharing

[poot36]

What does the lights on the laptop do with just the power adapter connected?  If nothing measure the voltage of the adapter when it is connected to the laptop.  If there is no power the reverse protection diode did its job and shorted out.  Try and find R3042 AC in and see if it has power.  Also check that none of the mosfets in the power path have shorted out.  If possible find a schematic for this motherboard.

[Watth]

Thank you for your reply, I really appreciate.

What does the lights on the laptop do with just the power adapter connected?

It is off. Earlier, it was solid orange which, in normal conditions, means it is plugged and charging the battery.

If nothing measure the voltage of the adapter when it is connected to the laptop.  If there is no power the reverse protection diode did its job and shorted out.

I can mesure 19V on PCE6001 (net A/D_DOCK_IN)

Try and find R3042 AC in and see if it has power.

I got about 633mV

Also check that none of the mosfets in the power path have shorted out.  If possible find a schematic for this motherboard.

For now I only have the fz and PDF I shared. They are not for the exact Rev, but for now everything matches.

What would be the best way to identify and test these mosfets?

[poot36]

Ok, it is good that you still have power flowing on the board.  The AC in pin should be of a higher voltage but I could be wrong.  Try and find the datasheet for the keyboard controller chip (the EC chip in the docs you linked to).  It should give you an idea as to what voltage that pin is expecting.  The mosfets are small black squares that have 8 pins total (4 per side) with 4 of them on one side all connected together and on the other side 3 connected together and 1 connected to a skinny trace (this is the control gate pin).  You can check them with the diode mode on your meter.  If on any of the pins they show 0V they are shorted and are bad.  There are two of them by the black tape next to the power jack in the first photo (there is also a green and wight current shunt that you can check to see if it has gone open circuit as well.

[Watth]

You can check them with the diode mode on your meter.  If on any of the pins they show 0V they are shorted and are bad.
These mosfets are P0903BEA http://www.unikc.com.cn/UploadFile/products/2015710163158-UNIKCP0903BEAREV1.0.pdf.
While checking PQ8802 (the one nearest to the yellow jack J3901) in diode mode, I have 0V between drain and source (com of the multimeter on source) or the opposite.
For the other PQ8801 'the one partly obscured by the black tape), open circuit with com on source, about 470mV the other way around.
 
Is PQ8802 the culprit?

[poot36]

PQ8802 is most likely dead.  If possible remove it from the circuit to make sure.  PQ8801 has a high chance of being fine as you are reading the body diode in the mosfet (it still could have failed open but highly unlikely).  Here is the datasheet for the battery charger IC: https://encrypted.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0ahUKEwjD3NyF2snNAhVY3mMKHbbzDcAQFgg0MAU&url=http%3A%2F%2Fwww.mouser.com%2Fds%2F2%2F405%2Fbq24735-439508.pdf&usg=AFQjCNFy1P3xXXdva1FYXqqLp_DvZO4CiA&cad=rja

[Watth]

Again, thanks for you replies.

Try and find the datasheet for the keyboard controller chip
Not easy to find, this one! I mailed ITE Tech in the hope they can provide it.

If possible remove it from the circuit to make sure.
I'll try to find a shop able to do this kind of job (removing the mosfet, and eventually solder a new one), since I am neither skilled or equipped for this kind os SMD job.
In the case the mosfet is K.I.A., is it possible to replace it with http://docs-europe.electrocomponents.com/webdocs/13c0/0900766b813c0757.pdf? This allows me to have them really faster than ordering them from asia. As far as I could see, the specs are all at least better than the original P0903BEA.

[poot36]

If you can't find the datasheet for the keyboard controler chip don't worry.  I think at this point you should be looking at the datasheet for the battery charging circuit that I linked to in my previous post.  I would also check all the mosfets near the battery input as well for damage just incase.  As long as the replacement mosfet has a similar on resistance and current and voltage rating it should work.  Try to stay within +-20% for the current and on resistance.  I have personally have used a 20 amp rated mosfet in place of a 35 amp rated one in this type of circuit and have not had any problems.  I would think as long as the mosfet has at least 2 times the current rating as the maximum current the power adapter can supply it should be fine.

[Watth]

I know I'll sound stupid: what should I look for in the bq24735? Short on some leads?

[Watth]

As long as the replacement mosfet has a similar on resistance and current and voltage rating it should work.  Try to stay within +-20% for the current and on resistance.  I have personally have used a 20 amp rated mosfet in place of a 35 amp rated one in this type of circuit and have not had any problems.  I would think as long as the mosfet has at least 2 times the current rating as the maximum current the power adapter can supply it should be fine.

The AC adapters are rated respectively 4.7A (asus) and 6.32A (compatible).
For the replacement mosfet, I found the Fairchilf FDMC8462 (http://docs-europe.electrocomponents.com/webdocs/10c9/0900766b810c9637.pdf) max ratings: 40V, 64A, 9.3mOhms.
I'm trying to test every mosfets for short I find. For now there is none else than PQ8802.

[poot36]

The Fairchilf FDMC8462 mosfet will work just fine if not better then the original mosftet.  Lets hope it is the only failure.

[gnavigator1007]

I started my day like every other day reading the newest posts on the forum.  Not sure how I missed this one. I'd been scouring the internets on a similar hunt for the same mobo today.  Got quite the laugh ending up back on this forum.  Thanks fellas and please keep this updated.  I'll post anything I find, but so far this thread has been more help to me than any of the other stuff I dug into

[Watth]

The latest news:
I was annoyed by not finding a shop to do the reworking job, so I invested in a reworking station: http://www.antex.co.uk/soldering/soldering-stations/760rwk/; which I got it at 150€ (!)
I am now training on dead/obsolete mother boards. I order kapton tape with the replacement mosfet; they should arrive on Tuesday or Wednesday...

Oh, and I had a proper inauguration of the station by burning my fingertip, as one is expected with this sort of equipments.

[poot36]

When I clicked on that link it showed up as £314.16 so I think you got a deal!  When I got my rework station it was around $120 or so (but took almost a month to get here from China).  I have yet to burn my self with the hot air but have many times with the soldering iron part.

[Rasz]

so I invested in a reworking station: http://www.antex.co.uk/soldering/soldering-stations/760rwk/; which I got it at 150€ (!)

of course you did, its worth around 30 euro
http://www.alibaba.com/product-detail/Bakon-2-in1-rework-soldering-station_60437257941.html
Bakon is the original manufacturer, antex just switches soldering iron for an outdated handle they sell for probably 40 years now just so they can sell you non standard 40 pound tips

[Watth]

so I invested in a reworking station: http://www.antex.co.uk/soldering/soldering-stations/760rwk/; which I got it at 150€ (!)

of course you did, its worth around 30 euro
http://www.alibaba.com/product-detail/Bakon-2-in1-rework-soldering-station_60437257941.html
Bakon is the original manufacturer, antex just switches soldering iron for an outdated handle they sell for probably 40 years now just so they can sell you non standard 40 pound tips

At least I didn't pays 387€ (http://fr.farnell.com/antex/760rwk-eu/station-de-soudage-60w-230v-prise/dp/2422172) or 421€ (http://fr.rs-online.com/web/p/stations-de-soudage/3440697/). Those two prices exc. VAT (20%).
I wonder why these prices are so different.


Edit: the tips are 'only' 7.43€ at Farnell.

[Watth]

HOLY MAGIC SMOKE!

It works, nom d'un petit bonhomme, it's alive! ALIVE!
I owe you one, poot36.

[poot36]

Did you get my PM?