Problem with stuck magazine....
OK I have had exactly the same problem and spent the last hour or so fixing it.
It seems to have its logical knickers in a twist after the battery going flat and won't eject because its left a CD in the playing position, IE, out of the magazine.
So, remove the changer from the car (usually velcro then pull off the two phono and the power connectors) and undo the four small cross head screws holding the case on.
Pull the front panel off (you may need to pinch the case in the middle top and/or bottom as there is a clip here holding the front panel), then either pull the sides of the case out until the two rotary Horizontal/vertical mount controls disengage (or you may be able to rotate them anti-clockwise until they pop off, but I didn't try this) and lift off the lid.
Next, pull the four little mounting posts on the internal deck assembly out of their four rubber mounts on the outer case, and disengage the two springs from the horizontal/vertical mounting controls.
The mech is now loose inside the case but be careful as its attached by a rather delicate ribbon cable to the outside cables and connectors, This will unplug after you pull off the sticky tape holding it to the chassis, but you might be able to do the rest of this without unplugging it if you turn the mech over carefully.
You will see a motor assembly and several white cogs (actually you will see two but the little tiny one with a worm (spiral) drive only moved the CD mech optical head so ignore that one).
Using a small screwdriver, carefully rotate the cog closest to the motor so that (viewed with the motor closest to you and to the right) the plastic parts under this assembly start to slide to the right. You should actually be able to see the CD underneath start to move to the laft, back into the magazine, and the CD mech will open up to release it.
Once the cog doesnt want to turn any further (and the CD is completely back in the Mag), then you will be able to manually eject the mag by pulling sideways gently on a round white part on the mag side. The mechanism should click and release the mag.
Hey presto... fixed. Now just reassemble the whole thing back into its case, probably a good idea to check that each of the CD's is correctly seated in the mag and that there is nothing wrong with any of them that could cause it to jam again, then go try it in the car prior to final assembly.
As we now know that this unit seems to be prone to throw a wobbly if its power is removed with a CD in it, I would strongly recommend that you eject the mag before disconnecting the unit for final assembly, assuming it all works OK now, or indeed any time you might have to disconnect the car battery for any other reason.
Hope this helps, it did it for me!
Mark