Laptop Motherboard Repair

[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

[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.

[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?

[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

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

[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).

[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'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

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

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

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

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

It is better to verify it twice.

[precision001]

Re: Laptop Motherboard Repair

I removed the first burnt 8 pin mosfet. I can't read what type it is, but the top of it says ph7sd.

[precision001]

Re: Laptop Motherboard Repair

Based on some information that I have collected, the unidentified 16 pin chip is a PWM controller manufactured by Intersil. That might explain why all the caps on the PCB opposite the CPU are showing shorted (with no power applied, of course). I wouldn't be surprised if the CPU itself is bad, but that's no big deal. The problem now is that I need to find another PWM controller, or this will never boot up again.

[aubrey52]

Re: Laptop Motherboard Repair

can you help me out dead laptop motherboards hp dv6000/6131od 434723-001
i need parts y6 on motherboard by backup battery. number on part
is 32.768KE i thank it a crystal
thanks
aubrey52. have a good day

[stj]

Re: Laptop Motherboard Repair

that's just a watch crystal.
32.768khz is a time standard.
*any* old motherboard will have one.

[aubrey52]

Re: Laptop Motherboard Repair

STJ thank lot
i found that out and order 3 from digkey
32.768ke
got in to day fix mother board
here is digkey part number SE2417CT=Nd
95 cent a prics
thanks
aubrey52

[precision001]

Re: Laptop Motherboard Repair

How did you know that part was bad? What problems was the DV6k exhibiting? Was the repair successful?

[precision001]

Re: Laptop Motherboard Repair

I have an AMD based DV6000 motherboard in pristine condition. No power. No burnt mosfets, and no caps appear to be broken/shorted. When connected to a power jack, the LED indicator lights, indicating that there is no short, at least not in the beginning of the power circuit. Where would you recommend I begin?