HP DV6 Laptop not turning on - Fused mosfet?

[smanet]

First of all, I'm very new to this sort of repairs. I have done some very small electric repairs but nothing involving SMD.
My wife's laptop is not turning on anymore after it went to sleep mode. I saw this is pretty common for Pavilion DV6.
I have found a video on youtube that explains how to open it, mainly to clean up the dirty of the years and replace the thermal paste on GPU and CPU.
So, after trying to disconnect everything, leaving only the motherboard and the power button attached, I have tried to turn it on without any luck.
I was looking for burned/fused components all around the board without finding any.
I have then decided to take off the heatsink and the fan.
That operation reveled what I have identified as a fused MOSFET (I hope I'm describing it with the right terms!).
It should be this one: https://www.fairchildsemi.com/products/discretes/fets/mosfets/FDMS7698.html.
Could you please let me know if I'm right, having a look a the photos attached?
I'm able to find spare parts of that component for around 4 pounds (for 10 pieces), however I'm without a soldering iron right now and I was wondering what would be the best for the job. So far, I have used only a normal solder.
I believe SMD components will require extra care and special equipment, which I'm happy to buy if it can resolve this issue.
Any advice for me?

Thank you in advance

[wraper]

You need hot air for this one. There is a thermal pad soldered to the PCB underneath, so you basically need to heat up the whole part to remove it or solder back. Probably doable with soldering iron, bet then you will need to preheat the board anyway, otherwise solder won't melt.

[Alex Eisenhut]

Meh, two irons with large chisel tips and flux and lots of solder. I've removed thermal pad parts like this, of course the part is dead after and you need the "touch" to not fry the pcb.

[Monkeh]

It's likely you can replace the whole board for similar cost to the tools required to have a chance of repairing it.

I'm all for repair, but if you've never tackled this sort of task, you're probably better off replacing it.

If, by remote chance, you happen to be in Cornwall, I have the tools.

[smanet]

Thank you all for the replies.

I understand that it's a hell of job, but I'm wondering if I can do it on my own.

I have found this on ebay: http://www.ebay.co.uk/itm/400778925552

Would that be enough? And what temperature should I use to don't fry everything?

Thank you again!

[Monkeh]

You'll need to get the part and copper under it up to around 220C, so you're not going to get anywhere with less than 350C aimed at it. Flux gel is also needed (I suppose you could get away with a flux pen, but gel is much better for these reflow times), which isn't cheap.

[System Error Message]

before you start repairing see about discharging static by disconnecting all power and battery and holding the power button. Than start diagnosing the board and repairs.

Some laptops are designed to fail within some years so find that component that is designed to fail and stop it working. If you think the mofset is fused which is also likely than try replacing it.

Hot air guns are good for working on PCBs but make sure to cover other areas first. If you plan on repairing laptops commercially you will need a decent one.

Louis Rossman has many videos on repairing various things, you ought to watch them. He also responds to PMs on youtube most of the time.

[smanet]

Thank you again.

I have tried to disconnect everything, even for an entire night. I have also remove the cmos battery without any luck.

Last time it failed, less than a month ago, the laptop fried the hard drive PCB.

I believe that the mosfet is fused, I have attached the photos to get advice if that could be a case.
However, I believe they're not supposed to have a hole

I don't plan to repair laptop commercially and, hopefully, this will be a one time only.
That said, I have used soldering irons in the past and I'm happy to own one.
Not sure if the one on the ebay link I have provided is decent though.

I would love to hear any advice on how to cover the other areas (in fact I was wondering if I was going to de-solder too many things with the hot air gun!).

I will try to watch as many tutorial as possible before proceed, I believe I will not have many chances to perform the same operation.

[Monkeh]

You don't have to worry about desoldering things, they won't move unless you move them. You DO need to worry about plastic parts which may melt. To stop that you need to avoid the hot air hitting them. If there's nothing plastic nearby, you're fine, if there is, a simple piece of cardboard taped to the board to prevent the air making contact will be fine, it won't burst into flames.

Again, for a one time repair, please examine the price of a replacement board and decide if it's worthwhile making the attempt.

[amyk]

Hot air, definitely hot air.

[smanet]

I was checking ebay for a spare motherboard and there only 4 and none in UK and only one in Europe.
Anyway, no less than 60 pounds (excluding vat and import duties I guess).

I know that it will fix it for sure, but I'm planning to keep to soldering iron and hot air for the future

Not sure on the quality of that one on Ebay though.

So I guess I can give it a try.

There's no plastic around the area, I'll watch some video to be sure that i'll try this right!.

Thanks again for the great advises!

[poot36]

That is the VRM for the CPU if the mosfet failed it most likely took out the CPU by applying the full 19V of the power adapter to the CPU.  Also this model is known for the video chip dying.  I don't think this is worth it to try and repair.  If you want to continue with the repair check all the other mosfets for shorts and also if possible check that mosfet driver is still working and is not also blown.

[smanet]

I hope that the CPU is still fine, I believe the mosfet failed gradually (if we can say that) as sometimes I was still be able to get some power light connecting the adapter.
I wasn't aware of so many GPU failing with this model, however this one doesn't have a Nvidia chip but AMD.
That said, it's the only mosfet I found in that state and I did look around the motherboard without finding any other blown element.
I have ordered a soldering station (I didn't have one and it may be useful to me) and the part (10 mosfet for 5 pounds and few pence).
If it works, great. If not, I still have my soldering station for another adventure
Thanks again for checking!

[poot36]

You may get away with removing the two mosfets the constitute 1 stage of the voltage regulator module (VRM) and it may still function.  Depending on how badly damaged the mosfet is even hot air won't remove it due to it effectively welding itself to the copper trace below.  Luckily yours does not look that burnt yet.  If you remove the burnt looking one and the one beside it you will effectively disable one stage of the VRM and it should stay on if that was the only damage to the laptop.  Or if you are lucky there may be a solder jumper that you can remove to completely remove power from the entire VRM and once again allow you to try to power on the laptop.  I recommend a solder sucker or deslodering wick or brad for removing the solder jumper if the board has one.  I just hope your soldering iron is at least 45W or more for removing the mosfet.  I have seen a few AMD APU chips die just like the Nivida ones so you are not out of the woods yet.

[smanet]

Thank you all again for all the recommendations.

With my new WEP 862D+, I was able to removed the burnt mosfet (I had to go up to 430C in order to remove it!) but I'm still not able to power on the laptop nor I see any light on when plugging in the power adapter.

Yesterday I have double checked the power adapter on both the power jack itself and from the connector (disconnected from the motherboard) that goes into the motherboard and everything seems fine to me (more than 19V seen on the multimeter).

However, when the connector is connected to the motherboard, I can see only very low voltages (in the order of 1.5/2V) and the two mosfet 4835d will became very hot.

A google search revealed that they're most likely the major cause when a HP laptop (DV6 or DV7 series) doesn't turn on at all, as they may be shorted.

I have a few questions:

- How can I test them? I have found some directions on how to do that with the multimeter in both diode mode or resistance mode on Internet but I would love to hear from you too. Especially, should I take them off the motherboard for testing? This is should be the datasheet for the replacement parts too: http://pdf1.alldatasheet.com/datasheet-pdf/view/519768/VISHAY/SI4835DDY-T1-E3.html

- What would be the best replacement part if one or more are failed? I can find "easily" them here: http://www.ebay.co.uk/itm/2-Unidad-SI4835DY-T1-E3-SI4835D-SI4835-4835-SOP8-100-Original-/172192029843?hash=item281771dc93:g:KsgAAOSwFqJWkpzk or on RS online (but I have to buy at least 20!).

- I'm trying to understand what the other two mosfet 4134 are for and if I will need to check them.

I have attached some images for reference.

Thank you again for all your help Much appreciated

[smanet]

Using instructions here: https://endless-sphere.com/forums/viewtopic.php?f=16&t=19645, it seems to me that both 4134 have failed, while 4835 look healthy.
I'm happy to remove them to test them off circuit, just wanted to confirm if the tests are fine, especially the first one.
I have used PIN 1 (S) and PIN 4 (G) and I got reads between 300 and 600.
For 4835, I have just inverted the polarities for the first test and they showed open circuit (multimeter only displayed a 1).

Another guide was this one: http://linuxehacking.ovh/2015/07/22/how-to-easily-test-n-channel-or-p/

Any feedback is appreciated

[poot36]

If you get any reading from the gate to any of the other pins when the mosfet is out of circuit it is bad (unless your meter can supply enough voltage to turn on the mosfet).  If you measure between the drain and source you should get no reading or a reading of the internal body diode depending on which way around the meter probes are.  If you get any other readings the mosfet is bad.

[smanet]

Thank you poot36!

I have followed all the guides and I have even taken off circuit the mosfet but they have all passed the tests.

I'm investigating now the IC power controller TPS51125: http://www.ti.com/product/TPS51125 and while checking the VIN pin, it should get 19V while I can see something fluctuating from 0.5 to 2.5.

I was checking this russian forum (http://notebook1.ru/forma1/viewtopic.php?f=232&t=76663&start=0) talking about it. Google translator helps

I think I have found the schema of board here: https://gofile.io/?id=LidOQ4 (I cannot attach it directly as it's 2 MB), but I didn't have time to give it a proper look and I'm also unsure if I will understand it properly

I was able to extract and add the pages relative to the charger, so they're attached here.

[Monkeh]

And now we play the hunting game.

For a start, verify B+ itself does not have a short to ground somewhere.

Seeing as PQ820 blew up, which is the high side FET of one stage of the CPU power regulator, money is on the fault being there. Remove PL807 to PL809 and check for a short to ground only on the FET side of them (the CPU probably will not appreciate your multimeter's voltage).

E: Oh right, it's socketed. You can actually just pull the CPU to make these measurements and leave those big inductors alone. You may need to pull the FETs or cut the jumper at PJP822 to verify B+ doesn't have another fault.

[smanet]

Thank you Monkeh.

It would make sense to me that the power will not reach the cpu power modules until I turn on the laptop.
Am I right in thinking that?

This is the reason while I'm not concentrating the effort of the zone when the mosfet fused yet.

I'll try to find a good ground to make all the reading of B+, but if you have any suggestion I will appreciate

[Monkeh]

Thank you Monkeh.

It would make sense to me that the power will not reach the cpu power modules until I turn on the laptop.
Am I right in thinking that?

Generally, yes.

This is the reason while I'm not concentrating the effort of the zone when the mosfet fused yet.

This is the area in which violent damage occured. It is the most likely place to find further damage. Any of the other FET pairs could be damaged (and with them, the CPU). Clear the already suspect circuit before looking elsewhere.

[smanet]

So I have removed the CPU and checked all the mosfet around the CPU power module but I couldn't find any suspect.
Unfortunately jumper PJP822 doesn't exist on the motherboard!

PQ812 and PQ813 are still getting very hot.

Measurements on the connector (Pin 1 and 2), on PC850 and on PQ812 (Pin 3) showed a voltage between 0.5 and 2.15, which I guess it's not correct.

Checked again the voltage of the power adapter and verified a 19.18V.

If you think that I should concentrate my effort on the CPU power module, I will go ahead and take off pairs of mosfet and re-test.

Do you have any good advise for me ?

[mich41]

Did you check all VSTBY lines (and B+) for shorts to ground? I mean - black on ground, red on line, see what comes up in "200 Ohm" and "diode" ranges.

[smanet]

I have tried that but I'm unsure if I have that correctly. Could you please point me some elements, based on the schema, where I should check the short for?
I'm really sorry but I'm really a novice to this, willing to learn a lot with this experience.

During my own tests, I got a possible short (diode mode showing 001.5 or less) between ground and pin 1/2/3 of PQ813 (one of the two mosfet which get insanely hot when the adapter power is applied to the board).

Again, I'm not sure if I'm doing this right.

Elsewhere I have read that hot components should mean that the component is broken, but I have tested them all.... I'm confused at this point

[Monkeh]

Measurements on the connector (Pin 1 and 2), on PC850 and on PQ812 (Pin 3) showed a voltage between 0.5 and 2.15, which I guess it's not correct.

This indicates a short to ground. Neother PQ812 nor PQ813 can cause this. Either B+ directly or the output of a supply fed from B+ has a fault.

According to the schematic and what pictures I can find with useful resolution, there are jumpers for isolating B+ from each rail. Find them, open them up (this will likely involve using a knife. Very, very carefully.), and go from there. PJP822 is the first one to try, for the CPU regulators. If you can't see it, remove the tape from the edge of the board.