AC adaptor for Dell Latitude CSx latptop

Hi Allan,

It just so happens, that in my desk drawer here, I have an adaptor which came from a Dell Latitude CSx laptop. The part number on the case is ADP-

If we can come to some sort of arrangement regarding the postage, you're more than welcome to it - and I'll get it sent over to you.

Email address should be valid, but despammed.com seems to be dropping a lot of emails at the moment, so probably best to reply on here if interested.

Gary

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.

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.

I don't know what I'm working with. That's part of the problem.

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.

It's almost certainly electric.

when you get the box open be careful. some parts near the power inlet could hold a high voltage.

Bye. Jasen

Thanks for the helpful advice, Jason.

-- Ignorantly, Allan Adler

• 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.

Jasen Betts writes:

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.

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.

yeah that's about it. usually there are only two interesing layers.

an ohm meter or continuity tester can help greatly with tracing circuits. if it's sensitive to low enough resistance it can work on circuits where some, or all, of the parts are still on the board.

the third pin may be for a different input voltage, or it may be used to detect the presence of the ac adaptor. - I'd check first to see if two of the pin contacts on the plug are connected together

Bye. Jasen

Thanks.

When I wrote about the 3 pins, I forgot that the the cable, just before arriving at the plug that fits into the laptop, has a kind of barrel shape along the way, like a snake that swallowed a can of beans. Most likely it contains some more circuitry that results in there being 3 pins. My naive guess is that it is just a simple voltage divider, possibly with some protective stuff against mishaps that would not occur to me. Maybe the third pin goes exclusively to recharging the battery.

nah it's probably just a lump of ferrite to stop EMI from escaping the laptop. especially if it's fairly heavy and sticks to magnets and never gets warm (unless in a warm place).

Bye. Jasen

The "Lump" is just a ferrite block to help meet FCC EMI radiati>jasen writes:

Thanks for all the help with this problem.

I soldered the wires together. It is a very ugly job of soldering but it works and the computer works when I use the AD adaptor now. I used electrical tape to cover the exposed wires and more on the outside of the box to try to keep the wires in one position, so I don't stress the soldered connections. Hopefully that will hold.

Encouraged by this, I'm eyeing an AC adaptor that used to supply power to my answering machine before the wire developed some internal breaks and started providing only intermittent connections. It is a NOKIA ACP-7U with an output of 3.7 VDC and 0.35 A. The main obstacle to getting it open seems to be a little nut. I went to several hardware stores, including Home Depot, trying to find a nut driver for it. It seems to be smaller than

I'm not actually sure of the measurement of the nut. It is recessed in a narrow hole, so I can't measure it directly. I was thinking of photocopying it, but the prongs are in the way.

Since this NOKIA AC adaptor has no purpose anymore, I would consider reverse engineering this one just for the experience.

I've still not found a local hardware store that has such a nut driver. I'm now fairly convinced that it is 5/32", but I don't really know. I looked online and found some places that sell such nut drivers, but I don't want to pay roughly $5 plus S&H for it, especially when I'm not absolutely sure of the size. So, I've been thinking about how to make a 5/32" nut driver. My first idea is to take a piece of steel tubing of the right size, heat treat it to make it more malleable and then to jam a 5/32" allen key into the hole to make the hole hexagonal, and then heat treat it again to harden the steel. I don't have a 5/32" allen key but but I could probably file a rod into hexagonal shape and then taper it so that the end fits in the tube. I'm not sure whether I'll do this. I started looking through archives of rec.crafts.metalworking to see how people make hexagonal holes and learned about something called a rotary broach, which is sold by http:/

find a bolt that fits a 5/32 allen key and lock two nuts on the shaft. you may need to grind down the size of the head a bit.

if it was made outside the USA could be 4mm, but 5/32 is probably close enough.

Bye. Jasen

Thanks. Yesterday, it dawned on me that I might be able to use a standard american hexagonal socket set screw, about which I have gotten all my information from one of French's books on drafting. I went to a hardware store that had set-screws of various sizes but they didn't have heads and they didn't have 5/32, but they did have metric. They said I can bring the AC adaptor in and they'll see if they can get one of them to fit. Using lock nuts on the outside (and presumably pliers) is a good idea. Since these set screws are open at both ends, I was thinking of using an allen wrench to turn it. Hardware stores around here don't seem to be very well equipped. Ordering single little items online or from catalogues is also too expensive. So, now I'm wondering what people use set screws or hexagonal socket bolts for, especially sizes like 5/32", so I can also consider scavenging them from discarded items.

I'm also considering whether one can improvise a nut driver in the following way: take a metal rod of the right diameter to just fit into the hole in which the nut is recessed. Maybe if the nut isn't in there too tightly I could even use a wooden dowel. Then cut the rod into 6 congruent sectors with cuts along the axis. Then remove a prism over an equilateral triangle