Re: AC adaptor for Dell Latitude CSx latptop


Jasen Betts <jasen-b@xxxxxxxxxxxxxxxxxx> writes:

On 2005-09-22, Allan Adler <ara@xxxxxxxxxxxxxxxxxxxx> wrote:

The adaptor is starting to fail. It fails to power the laptop unless it is
in a very specific position. I took a look at the exposesd wire with a
magnifying glass. There seems to be a thin plastic wire inside surrounded
by a kind of stranded wire that looks like aluminum. It is apparently the
stranded wire that has sustained the break. Now that I realize that, I'm
considering trying to solder it, but I've never done soldering with this
kind of situation before: first there is the stranding, instead of solid
wire, which isn't too bad, but also the fact that it surrounds the thinner
plastic (in appearance) wire. Also, it is right next to the black box, so
there is very little margin for error and not much to work with on the side
coming from the box. If someone has advice on how to handle this, it would
be welcome. I don't know whether it is possible to open the black box. If
so, I might be able to scrounge some more length of wire or replace it.

if you can, open the box, that sort oof repair in the wire done close to
the box is likely fail again soon. Some boxs have screws hidden under labels,
or under plastic plugs, or little rubber feet. Some boxes clip together,
others are glued, still others are full of resin. the glued boxes will often
open if tapped repeatedly and lightlynear the seam with with a hammer.

Thanks for your helpful advice. I didn't want to try to fix the adaptor as
long as it was at still working in at least one position. That ceased to
be the case recently and last night I looked up your year old advice and
started working on the AC adaptor. There are no screws hidden under labels
or rubber feet and it isn't filled with resin. Tapping the box with a hammer
didn't seem to work, although I can't say what would have happened if I had
been more patient and persistent. Instead, I hammered a screwdriver into
the seam in a few places and twisted it and eventually got the box open.
I saw a couple of little screws on the printed circuit board that were covered
with what looked like glue. When I tried to clear away a little of the glue,
the screw heads broke off. I had thought that they served to attach the entire
assembly to the bottom, which I'd had trouble removing, but that was not the
case. Breaking the screw heads had no discernible effect. Stressing the
bottom of the case a little created a little space between the plug that
receives the wall cable and the box. I inserted the screwdriver and widened
the gap (I don't remember whether I used the hammer) and soon I was able simply
to lift off the bottom of the box.

I'm not absolutely sure that the plastic looking wire in the center is
an electrical wire. The spark when it connects sometimes looks greenish,
like the led, so maybe it is really a fibre optic cable or something.

It's almost certainly electric.

It was stranded wire with white, apparently plastic insulation. There is a
rubber holder of some kind with a hole in it that is part of the wall of the
case and the cable to the computer passes through it. After I cut the
wire, I was able to slip this off. Inside the case, the wire became two wires,
one in white insulation, the other in black insulation. The former connected
to the white insulated wire forming the central cable described above. The
latter connected to the outer stranded wire that wrapped around the white
insulated inner wire. I cut away the damaged portion and exposed the wires
in preparation for soldering, which I plan to do today as soon as I create
a suitable workstation for soldering. I'll describe what happens and whether
the AC adaptor works afterward.

I am puzzled by a few things:
(1) the plug that connects the AC adaptor to the computer has 3 holes in it,
but there are apparently only two wires comprising the cable going from
the box to the laptop.
(2) The Dell representative I spoke to was quite certain I needed exactly the
right AC adaptor, and others, maybe on this newsgroup, have confirmed that
using a different AC adaptor might fry the storage battery. On the other
hand, there are only two wires going to the laptop and I don't see how
sensitive that can be.
(3) Pursuant to (2), it is natural to wonder what kinds of fancy things might
be going on in the printed curcuit board in the AC adaptor. I doubt that
I can analyze it. I don't even recognize a lot of the stuff on it, since
it looks a little to me like surface mount technology, which I know very
little about.
(4) Pursuant to (3), I'm just curious to know how hard it is to reverse
engineer such an AC adaptor starting with only one of them. I don't have
any plans to do so at the moment, but I like to know how in principle
that would be carried out. My naive guess, as I imagine doing it, is that:
(a) one constantly takes photographs of the device in various stages of
decomposition and of its components;
(b) one takes careful notes on where everything went, and in what
orientation, and in what order they were removed;
(c) one removes ALL the components and records all possible information
on their provenance and electrical characteristics;
(d) one photographs and/or photocopies the PC board on both sides (hoping
there are only two);
(e) one uses an ohmmeter to test continuity between any two possible
places that a lead to a component or terminal might go;
(f) one uses a CAD program to try to reconstruct the circuit from all
the above information and a simulator to analyze it.

How close is that to the truth?
(5) Pursuant to (4), assuming it is somewhat correct, one can then do the
same thing with AC adaptors of other Dell laptop models and see exactly
what is the difference between them.
(6) Is it conceivable that the answer to (5) does have something to do with
the third pin on the plug mentioned in (1)? I wasn't planning to open up
the laptop to look at it, since I am quite intimidated by laptops and
have never opened one up. I did build a PC from components a while back,
and it would be nice to learn how to work with laptop hardware; I just
need a reason for optimism.
--
Ignorantly,
Allan Adler <ara@xxxxxxxxxxxxxxxxxxxx>
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.
.

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