Sorry guys, I've got no benefit in this story but it really works.

First of all, the CD has to be demagnetized. There's been an article
bout this in one of the "Elektor" books and I tought at first it was an
april fool's day. Then after, it appeared its true, somer magnetization
may influence the path of the laser beam.

That's for the CD topic.

Now, if you us this guy's machine, you must be absolutely sure that
you've got no DC in the signal path, otherways, it will never work or
even get worse.

Cheers
Georges