Causes of CD player skipping?

Skipping
The player executes normal track play, but the music drops out or skips ahead or backwards, or gets otherwise garbled, during play. You might hear some clicks as the CD Pro attempts to track properly. This type of tracking problem is usually referred to as “skipping,” and may indicate that the CD Pro’s laser current is diminished or that its receptor diodes are failing. It will have particular difficulty reading low-reflectivity discs (e.g. CD recordable and rewritable discs) and discs that may not conform to Red Book specification (e.g. pirated discs or non-major label discs).

from Enco Systems:
Tribol Molub-Alloy 9890 grease is the lubricant recommended by Philips for use on the CD Pro family of modules
0.35 oz of Tribol 9890 grease is shipped to you in a narrow-tip syringe
Application of the very small amounts required on lubrication points is easy with this syringe. If it is worth change the lens and also make sure you lubricate the rail.

Claude  

Very good advice here guys. Thanks! for sharing.

Sony CDP-CX300 skipping - terrible skipping problem solved 

(modified post repeated for clarity)

I applied gun oil (a thin oil that says it has silicone in it) with a Q-tip to the single metal laser guide rail. That eliminated the skipping problem. Such a simple fix: remove the cover, dab a small amount of oil on the rail. Amazing that something that simple solved the skipping problem. I had observed that CDs always started skipping between 4.18 and 4:54 minutes. That was an indicator of a "location problem".

Detail: Remove the cover. Visually look for the metal guide rail (shaft). It is located at the rear left of the player (where the laser movement mechanisms are located) when looking from the front, and is seen in between the black plastic. The laser mechanism slides on it and this can be observed by powering the unit, selecting a disk, then increasing & decreasing track numbers on a rotating disk - the laser will slide on the rail. Now, reach into the access to the metal guide rail with a Q-tip moderately saturated with oil (3 in 1, gun oil in my case), and wipe along the accessible surface of the metal guide rail surface; the "backside" of the rail opposite the access area cannot be be reached for lubrication without further disassembly. But reach around "behind" the rail as far as practical. This lubrication task is very easy to accomplish and should have been included in the manual.

I had previously done some disassembly and cleaned the black "split drive rack"(gear), then re-lubed it with white lithium grease. [The pinion gear (not seen) and rack move the laser on the metal guide rail]. This lubrication did not solve the skipping problem.

These players are not sold any more, but it sure is convenient to load up as many as 300CDs - and avoid e-wasting an otherwise useful CD player.

So here's a weird one-
I cleaned and re greased the optical rails on my 200 CD Sony. Still skipped. As I was moving it, I lifted the back left end up (where the optical assy is located) which took the weight off the back left foot. It started playing fine, no skipping. I then Placed a spacer under the back side, just enough to take the back left foot off the tabletop. So far is playing fine.
Somehow the back foot of the case is tied in and stressing the optical assy to go out of alignment(?)
It's playing, so don't care at this point.