This just as a note, if someone's interested...

My DVD player, a Pioneer DV-535, had problems recognizing DVDs. Some
would work, some would not. Sometimes a little open-close-open-close
workout would be necessary with the tray to get a disc working.

So I took it apart. Observing the lens while loading a disc, it was
obvious that focus was not being obtained. The lens made two passes
with the red laser and then two passes with the IR one, then gave up.
There were not many adjustments, the only ones being for the laser
powers (there are two). They didn't help anyway.

Fumbling around in there, I noticed that lifting the disc edge with my
finger allowed the pickup to focus every time. I guess the suspension
(or something) is beginning to sag and is causing this problem. I fixed
it by removing the spindle motor assy (three screws) and installing it
with cardboard washers, cut out of a business card. This raised the
disc just enough (less than 1 mm) to allow focus to be obtained. I did
this about six months ago and the player hasn't failed me since.

The player still makes the noise that other users have also been
complaining about. It appears that the disc clamp doesn't quite center
on the spindle and this causes the whole thing to wobble a bit. Any
easy fix for this?

BR, Ilkka

FYI, I have a panasonic giving me the same "No Disk" error message.
Replaced a bad spindle motor only to have the thing giving me the exact
same message. I was afraid to touch any of the adjustment screws, since
this is probably a point of no return, but since the laser is
emmitting, and won't lock in focus, I suspect something needs
adjusting, or I accidently damaged the laser lens. Still working on it
though.