Sound completely out in mono mode, distorted in stereo mode.
Assuming that you've tried plugging the headphones into a different device to check it's them, not the CD/MP3/whatever, that's at fault, then the most likely problem is a break in the screen of the headphones' cable.
If you have a multimeter, you could confirm this by measuring resistances. If you look at the jack plug, you'll see it has three conductors to it called (reading from the end) tip, ring and sleeve. With the headphones set to stereo, you ought to see a few tens of ohms between sleeve and tip; the same between sleeve and ring; double that between tip and ring.
My guess is that in your case, you'll only get a reading between tip and ring, with the two readings involving sleeve both showing open circuit.
If you can see gross damage on the outside of the cable (where one of the children has ridden over it with a office chair again), you probably need to replace the whole cable.
If there's no visible damage, the failure is usually just at the point where the cable goes into the jack plug (all the stresses when you move about are concentrated there). You can often prove this fault by wiggling the cable around while pushing it into the plug and seeing whether sound is intermittently restored. Solution here is to cut the last couple of inches off and fit a new jack plug.
You will be able to buy lightweight screened stereo cable (if you need it) and a stereo jack plug of suitable size (the standard sizes are 3.5 mm and 1/4" - referring to the diameter of the sleeve) fairly cheaply from a hobby electronics shop (is Tandy/Radio Shack still on the go out there?)
If you have to change the cable, use the way the old one is fitted as your guide to fitting the new one to the headphones.
Either way, you'll need to fit the new jack plug. Don't forget to put the cover over the cable before you start to wire up the main terminals.
Jack plugs usually come with solder tags. Of the two in the middle, the one on top is connected to tip, and the one underneath is connected to ring. The tag for sleeve is combined with a cable clamp usually just as a single hole halfway up the clamp.
Strip the cable so that the insulated wires will reach the tip and ring solder tags, the bare screen(s) will reach the solder hole on the clamp, and the crimp grip at the top of the clamp will work on the sleeve of the cable.
Double-check that the cover for the plug is already on the wire.
Solder the red wire to the tag for ring (the lower of the two in the middle)
Solder the other coloured wire (usually blue) to the tag for tip (the upper one in the middle)
Solder the bare wire screen (both of them if there are two) to the cable clamp at the point where the hole is drilled through it.
After all your soldering has cooled, use a pair of pliers to bend the arms at the top of the canble clamp around the sleeve of the cable and crimp to secure it all. Screw the cover onto the top of the plug.
That should do it.
A.
