how do printed circuits break?

Physically broken/cracked surface mount components or the solder connections to same. Rarely visible to the naked eye.

Is it practical to try to diagnose it further, and if so, how?

I won't bother with the phone (it's cheap), but for the laptop I couldn't locate a replacement motherboard, and getting a completely new one is expensive.

Is it possible to fix a motherboard if it has such problems somewhere (broken/cracked surface mount components or the solder connections to same)? If so, what kind of equipment, knowledge and time commitment will I need?

It can be done, you just have to narrow down the fault to as small an area as possible and resolder everything. I've seen this sort of problem a lot of times with vias that go from one side of the board to the other, expansion and flexing breaks the plating between the layers and you get an intermittant connection with nothing visible.

In the days that PCBs were expensive, so you could take an hour or more to pinpoint the fault, our techs used an hair dryer and a can of coolant. Of course, experience was the other half of the requirements. The latter faded away when the repairtime/board shrinked. I still own a working XT of which the motherboard was rejected as the fault could not be located within half an hour. I got it for a small contribution and made a running machine in one evening. These days PCB repairs are rare, very rare. That's to say for professional/commercial use. Even boardswapping becomes too expensive in some cases. It has been six years now I bought a monitor. Within warranty time it was swapped as a whole. After three years, when warranty was over, it was said to be unrepairable and I was advised to buy a new one. To make a long story even longer: Cans of coolant are still available but I'd use a hot air soldering "iron" for the hot part. Components became very small you know. Besides, you'll need lots of time and even more lots of luck. Nevertheless it may be worthwile to give it a try. Good luck.

petrus bitbyter

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alex goldman wrote:

Cold solder joint(s). Sometimes undectable to the eye even with the use of a lens.

Using your "bending" technique to locate the suspect region of board. Then, use a thin plastic 'probe' to poke at individual solder joints until you find it -- or, at least better localize where the problem exists. Then, re-flow solder all the joints in the area.

Google on "cold solder joint" -- _using the quotes in the search arg_

Jonesy

--
  Marvin L Jones     | jonz         | W3DHJ  |  linux
   Pueblo, Colorado  |  @           | Jonesy |   OS/2     __
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I don't think I understand: what did they use a hair dryer for? If it were hot enough for melting solder, its manufacturer would probably get in trouble with the intended customers.

I didn't know these things existed. How can hot air (plasma?) be more localized than a thin metal stick?

Regardless, I wouldn't want to spend $500-2000 on something that won't help me localize the problem anyway.

Microscope - and maybe x-ray the board. I would only do it if it was my prototype coming back from testing ...

Hardly Ever - Only *If* it is someting trivial like a component visibly cracked or fallen off or *maybe* a pin on an IC not soldered in properly. Often it will be a broken via inside the PCB or a joint underneath a 480 pin BGA, in which case you need the x-ray machine.

Ebay for "SMD" rework equipment. In general it will be cheaper to buy new than the salary you would have to pay yourself.

I suspect it's either the chipset or the GPU (both soldered directly onto the mainboard). Before spending $1000+ on a new laptop, I think I'll try heating the pins with a regular soldering iron (25 Watts) in the hope that the flaws, if any, will heal themselves. Is this a good idea?

Nope, not a good idea. You need to properly apply a thin coating of the correct flux over the pins after making sure the area is clean. You also need a proper temperature controlled soldering station for the type of solder that is going to be used. I typically use a silver based solder for this type of rework as it flows smoother with less beading up.

The more common problem on laptop boards is the via will become dislodged and there is no real way to fix it without very expensive equipment. These are multi-layer up to 16 circuit boards and you have no access to the internal layers.

It does not hurt to do a good full visual inspection of the components you do have access under a well lit 40X magnifier while moving the board. With experience you learn what to look for on the board.

to

An hairdryer usually didn't have go too high, for melting solder there's needed 300°, if an hayrdryer can go to 300°, probably we didn't have hair anymore ;-)

I.

Hello?

I plan to open up my laptop again - I need to know which end to stick the hair dryer in :-)

"alex goldman" skrev i en meddelelse news: snipped-for-privacy@yahoo.com...

Forget it already. It's unfixable. The problem is now componded by you have messing around with it so everyone will see the tampering and refuse to do anything with it!!

Leave it on the front seat of your locked(!) car - or ship it as luggage while travelling - then have the insurance pay for a new one ;-p