Laptop Motherboard Repair

[precision001]

Re: Laptop Motherboard Repair

New information:

I was lucky enough to have another one of the same model come in, with a power jack issue. I took a close look. It looks the same, except that the 4704 isn't a 4704 but instead a 6690AS. The other 8 pin mosfet is a 4800B and the 16 leg chip is a 68CAZ (G801FG). I wonder if I can replace the two chips on the bad board with the same chips I read off of the intact board. I'm concerned that because the other Satellite P205 used a 6690AS instead of a 4704, that the other two chips may be different as well. I believe that a 4704 is a P channel and that the 6690AS is N-Channel, I'm looking for verification on that right now.

[Pyr0Beast]

Re: Laptop Motherboard Repair

Can you make out even a few letters ?

..

Otherwise, unsolder everything burned. Both mosfets, burned chip and try to 'boot'.

Do Mosfet traces lead to this IC ?
It might be a battery charger controller IC.

[precision001]

Re: Laptop Motherboard Repair

This one looks a little harder than I thought. I can read that one good mosfet is 4704 - the other is too damaged to read, but from what I can read, it doesn't match up to the 4704, so I think it is something else. I have no idea what the 16 pin chip is, but it appears to be damaged as well. I have measured zero resistance from the inductor visible in the picture to ground, and all of the small caps mounted on the PCB on the opposite side of the CPU are shorted.

[Pyr0Beast]

Re: Laptop Motherboard Repair

Yes, pick one good ground and poke around with the other probe.

There are no relays nowdays afaik
(perhaps only for a modem?)

[precision001]

Re: Laptop Motherboard Repair

I'm not sure how I should be checking voltages or what I should be looking for. Should I be checking the caps near the inductors? About the sound - it was almost like that of a relay switching on and off - in a very controlled pulse - almost like it was designed to do that.

[Pyr0Beast]

Re: Laptop Motherboard Repair

I order (only) from farnell.com
They have proven friendly and reliable.

I had Aspire 1360 in service. Power on but nothing, no HDD or fan spin. Cpu voltage sits at 1.00V.
If it is a harsh sound, like you hear hammer knocking on some metal, I would guess upper mosfet is defective. But that is only a guess. However, you do know that sound once you hear it.
If it is tick-tick-tick, that is the overcurrent protection kicking in.

Probably there is a bad contact somewhere near it. How's with the voltages ?

[precision001]

Re: Laptop Motherboard Repair

I have an interesting one now, an Acer aspire. It powers on by itself but displays no video. Reflowed GPU - no effect. Pressed slightly on Max8760. Afterwards, board would beep one time each second. Strange beeping sound, almost like a blinker in a car - and I was unable to determine where it was coming from. Reflowing 8760 stopped beeping, but still no video. The 8760 is the dc-dc for the CPU, and the cpu is cold when power is applied. NB & GPU get warm, but not CPU. Could this mean that the 8760 is bad? I ordered some samples just in case. I checked the resistance from the inductors like you said previously, nothing below 20 ohms. No visible damage and no obvious shorts (checked caps).

[precision001]

Re: Laptop Motherboard Repair

Do you know of a good supplier of mosfets? Most places won't sell them in quantities of less than a thousand.

[Pyr0Beast]

Re: Laptop Motherboard Repair

I use a big electric heater for that purpose. Ceramic? heaters, the ones that glow bright orange. Since PCB absorbs IR quite well, there are no problems with it. I just place the whole thing on the table so mainboard sits on top of it. It uses around 400W and it is fairly enough to heat the PCB all the way to 200°C or more. Hot air gun does the rest
(I also place a small drop of SMD paste on top of the chip. Once it melts completely, temperature for reflow has been reached)

I sometimes pick the same type of mosfets that were 'blown' if I have the chance. Esp. in TV equipment, I don't like to alter circuits too much, might cause unpredictable results. However, sometimes you do have to do it.

Otherwise, you need a replacement. My first selection is by package. Next are operating voltages, Vgs (20V) and Vds (30V) - for most laptops. Then, from what is left, I choose the one with low Rds(on) and low gate charge. If both are better than the one that was already 'installed' I go for it.
Most circuits aren't critical, but it is sometimes preferred to reduce switching losses by replacing upper mosfet with the one that has low gate charge and the lower with low Rds(ON).

You really have to look as you can get worse parts for more money. I usually just 'stock' some good parts and replace everything with them. They do cost more, but you get bulk discount, so that evens out.

(Also, you can look in manufacturer's diagram, what he used)

Mosfets aren't critical in linear-regulating circuit. Switching ones are more delicate. CPU/GPU VRM's are probably the only ones you really have to care about.

[precision001]

Re: Laptop Motherboard Repair

I have read a lot about problems with reflowing large BGA chips. It is usually recommended to use a preheater, to aid in uniformly heating the chip. Since I don't have one yet, I've adapted the "toaster oven" reflow for this purpose. I consider a toaster oven too crude for any type of reliable reflow, but it's great for preheating. I have successfully reflowed larger BGAs this way but would eventually like to get one of those airbath units.
Dealing with power issues, you must have encountered situations where you had to find suitable substitutes for mosfets. Datasheets rarely recommend a replacement, and ordering parts from China can take up to a month. Up until now, the only considerations I have taken when substituting mosfets was whether the mosfet was P-channel or N-Channel, and the pinouts of G-D-S-...
What other factors should I be taking into consideration when selecting a substitute mosfet off of a salvage board?
What other advice can you give on identifying and solving power-related issues?

[NxB]

Re: Laptop Motherboard Repair

Removing a BGA - fairly easy.
Putting it back.... a little harder.
A reball kit is fine but for bigger chips I'd want something a little better than a heat gun. Something timed and with an even heat spread.

[Pyr0Beast]

Re: Laptop Motherboard Repair

If one of those chips is shorted it will definitely heat up a lot. And they do go bad. But that stuff is obvious - rail is down.

I have never given much thought about the post card as I don't really need it. But it is cheap.
Reading reset is useful.

I don't have the scope capable of measuring the output of modern PLL's in range of 200MHz or more so I don't bother (much) with that (also, can't find a replacement either if I find it faulty)
90% of all damaged stuff is power related. I stick to that.

On and off would seem like a power faliure. Rails not coming up when they should. However, some HP workstations do give a similar faliure if they can't boot.

By reflowing you mean heating them up to the point solder melts and not removing them completely ?
I have had great success with graphic cards with that procedure. I don't remove them because I will never put that back on, however, I would like to try it. Money is the big issue with buying such equipment.

Stencils might work. Buth with more than 100 balls, there is a big chance something will go wrong. Old boards might be quite fun to learn on them

[precision001]

Re: Laptop Motherboard Repair

As far as BGA chipsets, I successfully reflow most. It's the ones that have been tampered with that I usually can't bring back. I have seen some terrible things done to BGAs. I have pulled out pennies, all kinds of metal and found burnt and blistered BGAs from home users with access to a heat gun and Youtube. I prefer to use soft, pliable metal (like aluminum) that can conform to the die cast without putting pressure on it. This seems to dissipate heat better - but I make sure to protect any caps with polyimide or kapton.
Completely removing a BGA seems so hard for me - I don't know why. I have not yet successfully removed a BGA chip, cleaned up the pad, and put the chip back on. Every attempt at doing so has failed. Either I can't get the chip to line up right, or something goes wrong. I am considering buying stencils for the most popular chipsets and reballing some of them - over and over again until I get good at it. They sell "dummy" kits online for training purposes but I would rather get a feel for real chipsets, and there's no shortage of bad BGAs out there.

[precision001]

Re: Laptop Motherboard Repair

I am currently experimenting with a simple logic probe. I think that with a logic probe, I may be able to check certain parts of a motherboard while it is powered on to check for faults. The problem is I am not yet sure how to interpret what I am finding. I am hoping that eventually the logic probe will help me identify bad mosfets, bad low-signal transistors and other bad chipsets.
Some technicians in India have found it easier to remove chipsets that are non-essential to booting/smps, such as card controllers and audio chipsets. Apparently if one of these is shorted (and from what I've heard - they do go bad), it can bring down 3.3 or some other critical rail, crippling the board and preventing it from powering on.
I also use a mini-pci express POST card with a M-M usb cable. With this, I am specifically looking for the motherboard come out of reset and see if is giving out any codes. If it doesn't, the first thing I check is the reference crystal or the clock generator itself. My reasoning behind this is that motherboards in which I have removed the 14.318 have been unable to come out of reset. I have not yet found a board that actually had a bad crystal, but have removed different crystals from working boards to observe the effect on the board, so that I would recognize the signs of a bad crystal. With 14.318 out, boards would power on, but display no video. Removing a crystal near the southbridge often prevented a board from powering on at all.
I have seen many HP motherboards (dv6000 and DV9000 series) that power on for one second then off - never fully powering on. I have not yet successfully repaired any in this condition, because I haven't been able to determine the cause of the failure. I can't get post code reading, I can't use a logic probe, but I do have my new leakseeker. Perhaps this new device will offer some insight into the cause of these failures.

[Pyr0Beast]

Re: Laptop Motherboard Repair

Yes. Sometimes driver output of the IC fails. It is rare but it happens.
It may even not completely fail, just so that it slows down the charge of gate, causing excessive heating.

[Wizard]

Re: Laptop Motherboard Repair

I had seen a notebook crater the N/P combo MOSFET in one IC (8 pin type) caused by bad switching regulator controller IC. Need to trace from their gate pins of this hot MOSFETs to the said IC and replace this also.

Cheers, Wizard

[Pyr0Beast]

Re: Laptop Motherboard Repair

Yes, any type of reading is a good thing. Except dead short. You do have to know that certain components do have their resistance in the mOhm range, may that not mislead you. I probe with a standard multimeter (unimeter?) in the diode range. If it shows from 000-003 it is defenitely a short. Anything more, like 020 is acceptable. It proves really useful to trace circuits, like which caps are connected together and to which line.

I have not had any mainboards in repair which had main rail shorted to ground. However I bought a few (7) dead ones (cheap-3€ a piece), fixed one of them to replace the other one in the laptop, both had water damage. But on one the bga chip was a toast (heating way more than it was supposed to. Desktops are quite similar with that, SB usually dies), the other one (I bought) had working internal logic so it was good for repair. Replaced the mosfets on 3.3V line and replaced TPS51120 chip. Had to rebuild some parts of the regulating circuit since certain pads were etched away. It took me a while to figure that out since copper was the same colour as PCB and I was removing what was left behind water with acid, so that automatically means, one swipe and copper oxides are gone as well. Hydrochloric acid is good because it doesn't eat copper (noticably), only its oxides, so it is quite good to clean it. There was no 19V on the chip due to eaten via - missing, so no way it could work.

Other mainboards are 'beyond repair', so mostly used just for parts. I cut apart one and made myself a nifty DC-DC converter 12V (or more) to 5V and 3.3V out of it. Some were hit by lightning which is quite obvious, burned pads and traces around LAN socket.

You will gain knowledge fast. I was repairing PC mainboards before I switched to repairing laptops. That knowledge is quite universal (interchangeable), both have similar faults. But PC's are more 'obvious'. No voltage to certain parts or just burned.
The first thing I do is to check voltage(s) (with no components like memory, graphic card on the board (however, no CPU will mean no voltage on that output). I have just repaired one gigabyte mainboard - DDR ram fet was open. It was brand new (meaning it never worked as it should from a start) and it was sitting in my 'to be repaired one day' bin for a long time. I noticed that just by accident, as RAM led was not giving any light. I have stumbled across a similar fault before, but the board was beeping (a good sign to see it is alive (internally), this one didn't do anything. It even didn't beep with no memory like it should (RAM error since no voltage for it to work), tho the speaker worked since it did made the POST complete short beep.

BGA's can be tricky sometimes since you can't see underneath. I have seen a great deal of damage caused by 'dust' in the connector, especially metal shavings (can also be from metallic layer over casing's plastic to give it greater strength). I always give the docking port connector a good sweep across the contacts and where it is soldered. Pins are just so incredibly close.
And you have all sorts of voltages there. From 3.3 to 19V. Something will definitely go wrong.

(this is getting a bit long now

It is difficult for you because that is a completely different world. It took me a long time (years) just to see what the obvious fault was, like burned mosfets and similar. However, I did not have had _any_ help. Everything was self-learned.

If you don't see a problem instantly, don't rush and don't worry about it. Seep on it and you'll remember a different approach the next morning.
I will draw a simple schematic tomorrow (today?) that will clear a few things up.

[precision001]

Re: Laptop Motherboard Repair

No, you are not checking the inductors.

Inductors are needed for switching mode converter. You need upper and lower mosfet (or diode) to do the switching meaning, where is inductor, there must be a switcher behind or infront of it.

Current thru the mosfets goes thru the inductor and into output capacitors. It would be the same to check output capacitors, to determine a short, but finding inductors is much easier
Measure between inductor and ground.

I've started measuring between inductors and ground. It always shows some kind of reading - which I guess it a good thing. This looks like a good standard check to do on any motherboard. As far as that Asus motherboard, I think substituting the 4407s may have caused more damage. I'm more interesting in gaining a better understanding of the cause of the failure than actually fixing that unit. I was working with a DV6000 motherboard yesterday that had 19v shorted - most caps showed shorted. I lifted about 20 caps before I found the bad one, but even after that it only powered on for a second then shut back off. I tried reflowing what I believe was a BGA mounted I/O chip, but after doing so the plain short strangely re-appeared - suggesting that 19V lines can be brought down even by bad bga chipsets. Motherboard repair is very interesting and I want to learn as much as possible and get better at it. What could I have done differently with that Asus board, and the DV6000, that may have changed the outcome of the repair attempts?

[precision001]

Re: Laptop Motherboard Repair

if you find a shorted rail - in anything,
a low-ohms meter will find the exact component real fast without lifting stuff.

years ago everybody built there own low-ohms devices - often using a speaker that changed tone.
very handy kit.

I bought one. I bought a leakseeker 82b. I can't find anything with it yet, I need more practice.

[Pyr0Beast]

Re: Laptop Motherboard Repair

No, you are not checking the inductors.

Inductors are needed for switching mode converter. You need upper and lower mosfet (or diode) to do the switching meaning, where is inductor, there must be a switcher behind or infront of it.

Current thru the mosfets goes thru the inductor and into output capacitors. It would be the same to check output capacitors, to determine a short, but finding inductors is much easier
Measure between inductor and ground.