Asus Laptop Repaired
Recently my friend Chafik asked my help in fixing an Asus Laptop of a customer that had a very big Short Circuit right after the DC Power input jack. The 19.5 V DC immediately short circuited in a degree that the Mainboard multilayer pcb completely had disappeared over at least 2 cm2 right behind the Input Jack. The current had ‘eaten’ the copper spores of the perhaps 6 inner layers and maybe also some of the outer layers on top and bottom. The epoxy had kind of melted over the complete area involved.
And the burning smell of copper and epoxy was really filling the service room with dislike because of the fumes after every new burning short current.
However the short circuit didn’t dissolve and the pcb kept on burning further. Something that is sadly nothing new in Repair, because bad short circuiting pcb’s keep on popping up so now and then.
The Asus laptop type N71VG we are talking about in this case, just wasn’t going to work and I noticed that the green led on the Power Supply (4.74A / 90Watt) went off after every new Short Current. But restored itself completely after about 15 minutes again! These Power Supplies are very new because normally they would break down internally after big Short Circuit Currents. And a repair would usually be necessary. But not with these very good totally new designed Power Supplies!
Next photo shows the gap that was burned because of the short circuit in the mainboard pcb.
Above photo also shows what needed to be modified to the pcb in order to dissolve the short circuit problem in the N71VG laptop multilayer board.
The 2 black parallel mounted input coils had to be removed because the short circuit was on their inputs. And therefore the 19.5V DC input voltage had to be connected at the endsides of both Coils (without leaving the coils in place of course). Also the Mosfet a typ 4538 (30V 9.6A) on the right of both coils was defect, being 490 ohm in one direction and about 370 ohm in the other direction. So that was another error that a replacement Mosfet type (also P-channel 30V 10A) 4407 couldn’t fix. Because that one also got defect after connecting with the measured Power supply 19.5V DC input. The replacement 4407 also was afterwards defect in 2 directions just like the original replaced Mosfet did. And measured out of the circuit equally defect like the 4538.
So because we also knew that the N71VG Asus laptop only worked okay when the input resistance at the Power Jack measured about 490 Ohm in one direction and very high in the other direction, we also simply had to remove the first Bad Mosfet 4538/or 4407 from the board.
The reverse polarity Diode that also was mounted at the board input circuit was still okay. And previous measurements on the Input Jack were taken with the Polarity Diode removed. This Diode is normally protecting the complete Mainboard behind it, from idiot users that try wrong Power supplies with reversed polarized Voltages. Simply by shorting the input voltage because it only conducts at wrong polarity.
And by connecting the 19.5V DC at the output side of the now removed first input Mosfet position. The Asus N71VG laptop should be working again!
But to show what had changed I will show you an example circuit from a HP Laptop/notebook that is compatible with the way in which most, if not all , Laptops nowadays are designed and working.
Above circuit clearly shows the incoming DC Voltage from the Power Supply going to the first 4538 P-Channel Mosfet (30V 9.6A).
The first Mosfet switches through the 19.5V DC to every other circuit on Board if the AC Power Voltage is active. So if our Mainboard pcb in this case is so bad at the input side that it keeps the entire Laptop from working we simply disable these components. And we put our 19.5V DC there ourself without having the necessity of this first switching Mosfet component that also acted as kind of protective circuit. But it is either this or a completely defect – throw it in the Bin – Laptop.
And I’m sure you’ll agree that there is no better way to solve the problem then the one presented here!
Hope that you all enjoyed this repair.
Albert van Bemmelen, Weert , The Netherlands.
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P.P.S- Note: You can also read his previous repair article below:
https://www.jestineyong.com/400-watt-pc-power-supply-repaired/
P.P.P.S- If you wish to learn how to repair laptop, you can check out the info HERE.
(105)Dislikes
(10)
25 Comments
Leave a Reply
Yogesh Panchal
November 16, 2015 at 4:20 pm
Albert , thanks for sharing the experiance.
Albert van Bemmelen
November 19, 2015 at 2:03 am
Thank you Mr.Yogesh. Also because you were also the first
that didn't dislike my article.
Albert van Bemmelen
November 16, 2015 at 5:15 pm
Addendum: This laptop N71VG laptop couldn't be fixed by another
'professional' repair shop in town. But after my modification
and removing the very Big short circuit in the mainboard
everything including the 2 HDD drives worked again as new.
But the Battery was totally useless and maybe even the cause of
the burned out pcb after the 19.5V DC Input jack. So I advised
the owner not to insert this old Battery anymore. And the
customer was more than happy that the laptop was working again
since the other shop had told her it couldn't be fixed!
Which proved to be a totally wrong conclusion after all.
Keep in mind that the presented Schematic was that of a HP/Compaq
Laptop and not of this N71VG Asus Laptop. Because the repaired
N71VG Laptop didn't have 2 Mosfets after the 19.5 VDC input, and
the HP schematic didn't have an anti-reverse protection Diode in
its circuit. That has to do with the fact that the first P-Channel
Mosfet also sometimes is used as a kind of anti-reverse DC input
protection like probably is the case in the HP/Compaq Laptop.
Parasuraman S
November 16, 2015 at 5:29 pm
Good Job! It is appreciable that you did not leave even a burnt PCB without trying it out! Very rarity, indeed! Good luck!
Albert van Bemmelen
November 19, 2015 at 1:56 am
Thank you Mr.Parasuraman. It is really not such a rarity at all because I've seen more of these burning pcb cases before! But it is the first time I wrote about it.
mmoni Diphera
November 16, 2015 at 5:37 pm
good exeperince
Albert van Bemmelen
November 19, 2015 at 1:57 am
Thank you for your appreciation Mr.Mmoni!
Gerald Millward
November 16, 2015 at 6:15 pm
Whew - well Albert, you're a braver man than me. I'm afraid I would have despatched this motherboard to the recycle bin without hestitation for safety reasons. A replacement motherboard is probably not economically feasible for this quite rare model, but I wouldn't risk it going up in flames. Good second-user laptops are freely available on eBay from reliable sellers.
Albert van Bemmelen
November 16, 2015 at 8:08 pm
I understand your hasitation Gerald. But there is no risc
here at all if you leave out the Battery since that probably
was the only cause of the partly burned out Mainboard pcb.
And the Power Supply itself was very well protected against
those long and Big shorting currents. As I mentioned above in
the presented article about these Very NEW Asus N71VG Power
Adapters!
These Battery charging problems happen more often than you would
imagine. (It is not my first burning pcb case I have come across
neither!).
And the Battery didn't work neither charge anymore but since
everything else worked splendid afterwards, there was no reason
to throw away a perfectly great working Laptop at all!! But you
are absolutely free to abandon a great working Laptop only because
it has a bad Battery pack.
Gerald Millward
November 18, 2015 at 5:28 pm
Albert - I'm sorry, but I can't agree that to repair a laptop in this way is safe. You don't really know what caused the short, or what other damage was done in the power layer. The burnt-out charging chip could be an effect, not the cause of the short. Laptop fires due to the failure of short-circuit protection systems are not uncommon - they are a last-resort safety device, not something to rely on as the only thing between you and disaster. To replace this laptop with a cost-effective 2U model from eBay is my safe answer. We must agree to differ I think.
Albert van Bemmelen
November 19, 2015 at 2:50 am
Hi Gerald, I have seen my share of laptop repairs in the
past 4 previous years.
Indeed what you are saying is what I said before
and that is the fact that the bad Battery Pack most likely
was the only cause of the partly burned pcb mainboard and
probably not the charger circuit itself. And because the
Battery now is kept out of the equation (it wasn't working
anymore anyhow), and the Laptop functions like new again,
there is nothing left that can explode or burn anymore.
Because also the short circuit in the pcb mainboard is
completely removed. And you are of course in your right
to replace it by a new board because this old board would
fall out of any guarantee clause by definition.
But who says that your new board in time will not get short
circuited too? You see it could also be a construction
or development error in all those boards or that series of
components (that same charge). Or a bad charge of Battery
Packs in this peticular N71VG model? Anyhow this Asus laptop
is completely working again to fully satisfactory of the
owner. And the owner is warned about the Bad Battery Pack
and the previous burnt short circuited pcb and will not
use any battery in it anymore. Nor will she leave it on
unattended while not at home.
But as I said before this laptop was okay in earlier years
until it automatically broke down and this repair was the
only remedy. Buying a new board won't prevent this from
happening again.
Robert Calk
November 16, 2015 at 8:04 pm
Good job getting the motherboard fixed, Albert. That thing looked like it was toast!!
Albert van Bemmelen
November 16, 2015 at 9:09 pm
Yes Robert, only with a quite different smell of course.
After I removed the Short Circuit at the Mainboard input,
the pcb burning had entirely stopped. And everything except the
Battery Pack was working like new again. You wouldn't
believe how many Bad Battery Packs, and burned Boards I
already have seen! No wonder with those short circuited currents
at 10 Amps or even more!
Muftah
November 17, 2015 at 1:56 am
Hi Albert,
Good work, it is saving from garbage.thanks for sharing.
best regards
Muftah
Albert van Bemmelen
November 19, 2015 at 1:53 am
Thank you Mr.Muftah. Glad that you liked the article!
Merlin Marquardt
November 17, 2015 at 5:43 am
Impressive.
Albert van Bemmelen
November 19, 2015 at 1:51 am
Thanks very much for your appreciation!
Albert Hoekman, Holland
November 17, 2015 at 6:27 am
Hi Albert, you did a very nice and respectfull job on this Laptop. What I like to know is the cause of the damage. To me it looks like a lightning stroke at the electrical house system. But then should the power supply also has vaporised.
Albert van Bemmelen
November 17, 2015 at 5:16 pm
Hi Albert. No there was no lightning, only previously burning
of epoxy and copper.
The battery pack kept shorting the current of the 19,5V Power
Adapter. Maybe the charger chip was gone defect too,
I don't know. But the damage to the Mainboard pcb was already
done when I got it for repair. So there was no reason to check
for the charger circuit because the Battery Pack was gone!
And as I explained in the article, the Power Adapter was the
first I ever saw that recuperated automatically from any short
current after a certain waiting period. Without any damage
whatsoever!
And because the laptop itself perfectly worked after the
shorting pcb input layers were removed, it was a very safe
and successful repair. A new Battery Pack could however still
have charged and worked normally, but because the first Mosfet
at the DC input didn't function anymore, THAT wouldn't be
safe in case of overcharging the Battery if also the Charging
circuit was gone too! But the customer was more than happy she
had her laptop back and working again when others told her it
was unrepairable. Which was evidently a complete lie. And they
probably only wanted to sell her a completely new Laptop!
According to all dislikes after publishing my article I think
most of the readers just do not understand how a laptop works
and when a repair is successful. And not every customer wants
to buy a new mainboard or laptop just because the Battery doesn't
work anymore. And just as not every engineer can fix these very
big pcb errors satisfactory either!
Suranga Electronics
November 17, 2015 at 3:44 pm
Super one Repair..!!!
Thanks.
Albert van Bemmelen
November 18, 2015 at 12:04 am
Thanks for your support. I'm glad that not everyone thinks it was a crazy repair!
Humberto
November 18, 2015 at 2:12 am
Albert, you have done a complex repair of this laptop, I reaally enjoyed reading your article, and you really deserve to be recognized with this repair: congratulations.
Albert van Bemmelen
November 18, 2015 at 5:00 pm
Thanks Humberto. I appreciate your kind words. It was a very big
short circuit indeed! But it was also the only cause why the
laptop didn't work before. But in case a laptop doesn't work and
there is no short circuit problem, other reasons can be the cause.
For instance : 1. The Bios Flashable chip can be corrupt.
2. Or there is no 3.3V on the Bios chip so it will not work.
3. There is no active 3.3V Power Supply working on the Mainboard.
4. There is no active 5.0V Power Supply working on the Mainboard.
5. The Video chip is defect or doesn't get power.
The Power Supplies can be found on the mainboard were there are
always at least 2 big square Resistors mounted next to two or more
Mosfets. But concerning all dislikes I got, I think that someone is
deliberately messing up all articles on Jestine's repair Blog. And
without mentioning why he lost all arguments!
Hicham
November 18, 2015 at 6:44 pm
Congratulations for this great repair, thank you Albert.
Albert van Bemmelen
November 19, 2015 at 1:48 am
I'm glad you liked it Mr.Hicham.