HOW TO FIX A WALL WART

          Repairing that little "throw-away" AC to DC adaptor

     They are usually glued together. You can open it by smacking it
repeatedly at the place the two halves meet with the handle of a
screwdriver. Keep striking it until you hear it crack (makes a hollow
sound, much like a cocoanut). Whack it all the way around until it starts
to separate. Wedge a small screwdriver tip in any place that will open far
enough, and smack the remaining glued spots. If you try to pry it open, it
will usually crack where you don't want it to. With a little practice, you
can open one of those without leaving any marks on the outside. 
     Now to the insides. Two very common problems with these devices are: 
1. the wire inside the cable is broken, or 2. there are bad solder
connections inside the box. Of course, there may be bad components, but
we'll check the easy stuff first. Most wall warts consist of a small
transformer, several diodes, and one or more filter capacitors. Voltage
regulation is usually done in the powered device, not the wart. 
     By the way, some warts are made with only a transformer inside the
box.  Obviously, that kind will only output an AC voltage. Rectifiers, 
filter capacitors and regulators will all be in the powered device. 
     The cable can break anywhere along it's length, but is stressed the
most at the ends (near the wart and near the connector).  Note: the cable
could be cut or "dog chewed" with breaks along it's length. To check for
breaks in the wire, plug in the adaptor and turn on the powered device,
then bend, twist and push the cable towards the case (don't pull on it). 
If the wire is broken inside the cable, it should make contact momentarily
and the powered device will come to life. If the cable is broken, the fix
is to cut off the broken end, and re-splice it into the box. You might
have to drill out the strain relief grommet. The cable is usually glued
in there and it is otherwise hard to remove. If the cable is broken at the
connector end, the connector will have to be replaced. They are usually
solid molded plastic and can't be opened. 
     Bad solder connections are easy to fix. Large electrolytic capacitors
are not always tied down and the connections break loose. Sometimes the
transformer and/or diodes are just not soldered properly. Reflow all the
connections on the PC board if in doubt. If the capacitor is bulging out
of the top or sides, or is leaking near the wire leads, replace it. The
diodes can be checked with an ohmmeter for opens or shorts.
     If the unit is dead and everything else checks OK, the primary of the
power transformer may be open. Check continuity with an ohmmeter. The
transformer usually opens because of an overload... either in the powered
device, or because the diodes in the wart are shorted. Transformers will
have a fusable link or thermal cutout under the plastic insulation.
Replace it ONLY with the same part for safety. It represents the only
"fuse". Without it, a bad transformer can get hot enough to start a fire.
Don't jumper it! 
     After repairs are completed, a few spots of super glue around the
edges of the half-shells and the wart is back together. Tie a rubber band
around it until the glue sets up. Hint: test it -before- you glue it! 
Lastly, if you're testing one of those adaptors, be mindful that it is 
connected directly to the power line! If the case is open, there is a risk 
of electric shock. Use caution if it is plugged in!!! 

Ray Carlsen
CARLSEN ELECTRONICS... A leader in trailing-edge technology.