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From: ChipInNC on 21 May 2010 11:01

The DC power cable going to the laptop has three conductors that are
layered similar to coax or audio cables. It has a single center
conductor that is wrapped with a (middle-layer) shield and then both
conductors are then wrapped again by a final outer shield. The layers /
shields optimize the cable for minimal electrical emissions and
interferences while allowing for maximum flexibility.

The center conductor goes to the center pin on the barrel shaped laptop
connector and is used as a data line to tell the laptop what "kind" of
power supply it is.

The inner (middle) layered "shield" is actually VCC / positive (+ 19.5
volts DC) and goes to the inside edge of the barrel connector (nearest
to the center pin).

The outer most "shield" is ground and goes to the outside edge of the
barrel connector.

During the course of use (and abuse) the cables tend to get damaged and
need to be repaired or replaced. The good news is that when the cable
has a short between VCC (+19.5 volts) and ground, the adapter usually
detects the problem and shuts itself down (no power LED) on both PA-10
and PA-12s.

If the center / data connector is shorted to VCC, the adapter may still
be protected on a PA-10, but will most likely be trashed on a PA-12 due
to the lack of a protection circuit.

NOW, WITH THE UNIT OFF AND TOTALLY UNPLUGGED FROM BOTH AC AND THE
LAPTOP...

Open the clamshell as listed above, and test the conductivity between
all three conductors at the barrell connector. Ground to positive,
ground to the center pin / data connection and positive to the center
pin.

They should all be open connections between each other. If there is a
short, between two or more connections then that will be the first issue
to fix.

Take the DC power cord and cut it off from the adapter at a point that
is closest to the rubber sleeve coming out of the adapter, but past any
obvious distress / exposed wires. This is our starting point.

Take a sharp knife and carefully cut the outside insulation from the
cord about 1.5 inches down from the newly cut end. Separate the shield
from the inner layer and twist it tightly. This is the ground
conductor.

Next take the inner conductors and remove the last inch of insulation
from around that shield. Separate the middle shield from the center
conductor and twist it tightly.

Now take the knife and remove about a 1/4 inch of insulation from the
center electrode and twist it tightly.

You may tin the ends of all three conductors with solder now if you
like.

Test all three contuctors for shorts and then for full conductivity
with their repective connections on the barrel connector.

If you found shorts or open connections, move up the line about 6
inches (or past wherever you suspect there is damage to the cable) and
re-do all the above. Continue until there are no shorts and full
conductivity to the connections on the barrel.

Keep in mind that you are also looking for intermittiant shorts / opens
as well.

** You may end up running out of wire and have to get a new cord **

If you do end up needing a new DC power cord, here's a vendor for them
($15 each though):

http://dcplug.net/dell.html

Let me know if anyone finds a better / cheaper source for these!


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