I noticed that this player had a sensor near
the disk spindle mounted on a small rectangular
board. Thinking that the sensor failure might
prevent the player from recognizing the disc
I decide to clean it. Because the sensor is
so far inside the disc loading mechanism and
difficult to reach I tried spraying the
spindle sensor with a can of compressed air.
After several blast of air, the DVD starting
seeing and playing DVDs and Audio CDs.

It is more likely that your blasting of compressed air on the disc drive
managed to blow out dust inside the optical pickup as well as off the surface
of the objective lens. DVD/CD lens cleaning discs are almost totally worthless
and are usually ineffective at fixing read problems. If anything, these discs
can cause damage to the pickup.

But, air blasting isn't a fix that will solve all disc read problems. Problems
that can yield similar symptoms include:

1. Marginal optical pickup
2. Tar accumulation on optical parts from smoke
3. Marginal photosensors
4. Alignment problems
5. Interface problems with drive and master board
6. Bad ribbon connection between pickup and drive electronics
7. Power supply problem
8. Disc mounting problems
9. Spindle motor problems
10. Bad mechanical limit sensor(s)
11. Faulty advance belt(s)
12. Pickup kicker mecha failure
13. Lack of lubrication
14. Faulty gain adjustments
15. Faulty offset adjustments
16. Bad control electronics

It's just that dust accumulation is a more frequent culprit that causes disc
read problems.

Tar depositing from cigarette smoke is another frequent, but far more harmful,
cause of disc read problems. This is because cigarette smoke tends to leave a
tarish residue behind that tends to build up over time on vital optical
components inside the pickup with consistent exposure to cigarette smoke.
Eventually, the deposits are enough to intercept the beam to the point where
the pickup can no longer reliably read the disc, and cleanup of cigarette smoke
damage is almost impossible to do. Tar deposits are almost impossible to
remove without damaging the optical parts to begin with, and that's assuming
you can dismantle and reassemble the optical pickup without effectively
screwing up the optical calibration or outright destroying the pickup in the
process.

To make long story short, smoking will damage optical pickups in DVD players,
DVD recorders, CD players, CD recorders, MiniDisc decks, and LaserDisc players.
- Reinhart