aiwa z 1800?

had problems with this not playing cds, took it apart and changed lens and header for discs.. one of the cogs was broken that is on the multichanger part, this was replaced, but now it wont close and makes grinding noises as it closes, the lens part engages but does not dis engage? the big blue cog spins only one way? which does not disengage the lens?? have i misaligned the cogs? thanks