On Thu, 07 Jul 2011 21:29:05 -0700, mike wrote:
Jeff Liebermann wrote:
I discounted the ribbon cable because it fails video ram test
and because it has the same problem at the VGA output connector on the back.
Is there something I'm missing?
Ok. It's not the ribbon cable.
I watched a bunch of videos, including that one.
Difference is that they all have a BGA mounted directly to the main board.
That intermediate carrier is the wild card. I don't know what to
expect except that it's a thermal insulator and have nothing equivalent
to practice on.
Well, the real test is at what point the solder melts. Try taking
small pieces of solder and scattering them onto a PCB. You might have
to glue them down with some Cyanoacrylate adhesive. Then play with
the hot air SMT rework gun to see what it takes to melt the solder.
I haven't taken it apart far enough to try to determine if the chip
or the carrier is where the fault lies.
I'll remove the kbd from my A31 and see what I can find. I don't
recall seeing a video carrier board, but it's possible. Hopefully,
you wont have to remove the PCB in order to do the reflow.
I have three temperature controlled air guns. I've made air nozzles
with baffles in the past...way past...to rework gull-wing and J-leaded
packages.
I've got zero experience with BGA and even less with two-layer stacks
of BGA.
Good. You have proper tools. Think of it as using a soldering iron
made of air. Practice with any PCB at melting solder and removing
parts. It's not a perfect analogy of the X31, but it will help with
the temperature and timing. I don't recall if the X31 uses ROHS high
temp solder, or leaded low temp.
I thought I'd build a hollow platform out of bricks and blast it from
underneath with a power-controlled heat gun while I watched the pre-heat
temperature.
I don't know if that will work. You're blowing air into a dead end
"box" canyon, where most of the air is going to blow back towards the
nozzle. It will probably spray hot air in a much larger area than
intended. Try doing it very quickly, and check the result with a fast
acting contact thermometer (thermocouple and DVM).
Then hit it from the top to reflow it. Sounds like reflow temp
is about 260C. Any recommendations on what air temperature
I oughta use to get there?
Nope, but I know how to check. Same trick with the tiny piece of
solder. Put it where it won't do any damage if it melts. Tack it
down with some glue. Add flux. When it melts, you're hot enough.
Thanks, I gotta go find some flux...
Try blowing hot air at a puddle of flux to give you a clue what it
will do. Most use alcohol, which might catch fire.
Lenovo X31 hardware service manual:
http://download.lenovo.com/ibmdl/pub/pc/pccbbs/mobiles_pdf/39t6189.pdf
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558