Thursday, June 20, 2013

Dell AC Adapter

I bring you today another chapter in my ongoing saga to squeeze every last minute of life out of my laptop.  About a month ago, my laptop randomly shut off.  Investigation revealed that I had managed to rip open the power cord by getting it caught between a table and the concrete floor.  I noticed that only bending the cable certain ways would cause the short.  So, I did the logical thing and wrapped the cord in duct tape and forgot about it.

Fast forward to last night, and the power indicator tells me I'm running on battery power; the led on the power brick is off.  I attempted to coax the cable into working, but to no avail.  I shut my laptop off to preserve potentially precious battery and went to sleep.

Attempt 1

This morning I removed the duct tape bandage and began to examine the tear in the cable.  The cable is similar to stereo cable from my last adventure, except (unbeknownst to me at this point) there is another layer of wire under the first.

I'll explain here that standard DC barrel connector have a ground and a positive voltage.  The ground is the outside of the plug, and the positive is the inside.  Similarly, in the cable, the ground is the outer wire, and then under an insulator there is the positive wire.  These are both wound around a common axis (ie coaxial).

The outer wire was almost completely broken, so I cut it and attempted to splice it back together.  The inner wire was in much better shape, with only a few broken strands.  I at first attempted to just wrap that up, but ended up cutting it and splicing as well.  I soldered these two up and used a multimeter to search for shorts between ground a positive.  I powered it up and detected 19.5 V between the ground and positive.

However, booting up my laptop with it confirmed my suspicion that there was indeed a third inner wire.  Dell conveniently adds their own third wire to standard DC cables for making more money through proprietary power adapter sales safety.  This third wire was shorted to the positive and I figured whatever it was connected to in the power brick was now destroyed.

The third wire is a data wire.  It sends a signal from the laptop to the adapter to make sure you are using an official dell adapter.  If not it complains, but still powers the laptop.  However, it does not charge the battery.  There was some debate online about if the battery would indeed charge, just a slower rate, but I did not get any charge over the few hours I had it hooked up like this.

Attempt 2

It just so happens that I had procured a second power adapter long ago.  In fact, this adapter was the second one.  The first had failed a few years ago.  It developed a noticeable kink near the power brick, and with that, presumably a short. 

I decided to open it up and have a look.  This video purports to show the adapter being opened.  Note the comments accusing him of faking the opening.  I'll agree that there is no way that was the first time he was opening the brick.  It took me about an hour to get mine open, and I had to use just about every method I read online or could think of.  I started with just a screwdriver, but that did nothing but tear up the plastic.  I put some alcohol, and then acetone in the seam, which also did nothing but begin to dissolve the outer plastic.  I hit it with a hammer on the corners, which along with constant attacks with the screwdriver did begin to weaken the adapters defenses.  I only stabbed myself with the screwdriver three times before I put on a glove.

While the adapter was weakened, there were some parts that were clearly intent on making a valiant last stand.  I ended up using a clamp to squeeze the bottom piece away from the top piece.  This still required a constant attack with the screw driver.  When it finally came apart, both parts of the plastic case looked like they had been gnawed on by a honey badger.

Now I pulled back the insulation to reveal the wire below.  While this wire was about half broken it didn't seem like the second layer of insulation had any holes.  It didn't seem like there was any short here.

I tested this with the multimeter and it confirmed the positive was separate from the ground.  However, moving the cable around created a short.  Further investigation revealed that the short was actually way up by the plug.  This was rather annoying as I had hoped to use this better plug.

Attempt 3

I began to rip apart the plug to determine what was wrong with it.  The rubber came off easily with a razor blade.  Once off, it was clear that the insulation between the two wires stopped early and there was a short.  I don't really know how this design could possibly work.  It seems to be just begging for the insulation the wiggle its way down a mm and create a short.

The two wires were shrink tubed and soldered on to opposite sides of the plug.  I had to get at least the ground wire free so that I could wrap the inner wire up to keep them separated.  The problem was the wires were encased in something similar to hot glue, but much more rugged.  I suspect it was just liquid plastic poured in.

It was quite strongly bonded to the shrink tubing.  I tried acetone, which seemed to help, but I still had to chip away with screwdrivers and wire cutters little by little until the wire was free.

I wrapped the inner positive wire up in some electrical tape, and then wrapped the outer wire as well.  I added several layers of duct tape around the whole thing for good measure.

Now I revisited the kink by the power brick.  Here I decided to use a bit of solder to keep the broken half of the wire together.  I did this and applied a generous amount of electrical tape.

I was pretty incredulous that this would produce a working cord.  I did a lot of testing with the multimeter looking for shorts.  Then I left it powered and did a thorough wiggle test.  It passed both of those, so I plugged it into the laptop.  The laptop recognized it as a fellow dell product and graced me by charging the battery.

No comments:

Post a Comment