Balky tray on Asus DVD RW drive

Well, your trick worked! I used a piece of the label that was stuck over the disc that covered the hole in the cover as the spacer. I couldn't have used anything much thicker, as the metal disc which is fixed to the larger plastic one would not have fit under the plastic tabs. The thickness of the label I used is 0.16mm.

I never would have figured that out myself, and am wondering how you did. I never gave much thought to how the media disc is held onto the spindle so it can spin up, and how it is relaesed when it is being ejected.
My thinking on the details differs somewhat from yours however:
And before I begin with my theory, let me apologize to you if you are an engineer or scientist, or just someone more knowledgeable than I am on the subject.

On inspection of my drive, I found that the magnet is not actually the metal disc mounted in the larger plastic disc which sits in the hole in the cover, but is an electro-magnet "wrapped around" the spindle itself. The small metal disc above it is the ferrous material that is pulled towards the electro-magnet in the spindle when it is energized. This causes the media disc to be squeezed between the spindle and the metal plate - which is secured to the larger plastic disc with small tabs, allowing it to spin up. The disc above the media CD or DVD spins with the CD when it is engaged to it.
When the disc is being ejected, the electro-magnet is de-energized, allowing the spindle and metal plate to lose their magnetic attraction, and the media disc to disengage from the spindle. Only then can the tray slide out.

I believe that we are dealing wth "residual magnetism" in the spindle's magnet, the metal plate, or both.
When there is no disc in the drive, the attraction between the magnet and plate is slightly stronger, as you explained, and any residual magnetism would be more likely to hold them together. This would prevent the tray from sliding out.

When there is a media disc in the drive, the distance between the magnet and plate is greater, so the effect of the residual magnetism is reduced, allowing the spindle to separate from the media disc and the disc and metal plate above it, and the tray slides out.

The reason there is residual magnetism is poor materials chosen for the magnet's core and the plate. The metals are too "hard" and, after time, there is a small amount of magnetic energy retained by one or both parts. This is the definition of residual magnetism.

You really helped me out here. As I said earlier, I never would have thought of this as the cause of the problem with the drive. I am curious now as to how long the thin paper I placed between the metal and plastic to increase distance between magnet and plate by only 0.16mm will keep the drive working. I would suspect that eventually, the residual magnetism will increase to the point where we will be right back to where we were before the fix, or if the tray motor becomes just a bit weaker still.

If the problem does re-appear, I would like to test my theory by de-magnetizing the two components (the magnet on the spindle, and the ferrous plate). I can do this by exposing the components to a strong AC field for a short time.

Again, I thank you for sharing this information with me.

FW

Wow! I didn't remember posting the question, but thanks for the reference. Now I know how old the Plextor is. It will be due for replacement soon, as it has a problem as well.
I suppose that reversing the leads to the spindle's magnet would also do the trick of de-magnetizing the ferrite, since it would change the polarity 180 deg. But that would most likely involve cutting traces on a pcb and soldering jumpers.
I used to have a cassette head demag tool, but it burned out after a few years of use (was a Radio Shack model). I can build something like that in a few minutes, then power it with a doorbell transformer, or the AC line on a Variac set very low.

I had forgotten about the inverse square law. It's been a while...

Let me ask you about the Plextor drive, since you seem to know a lot more about these things than I do...
That drive seems to be reading at very slow speeds. If I insert a music CD, the fastest read speed I get for album tracks of 6min or shorter is 16X, while the Asus drive reads the same tracks at up to 24X.
But when I inserted a CD with only one long track (Jethro Tull's Thick As A Brick), the Plextor's read speed kept increasing until it reached 32X, and remained at that speed for the remainder of the track.

So I'm thinking that maybe the disc takes longer to get up to speed in the Plextor than it does in the Asus. Or, it could be the cache RAM size. I think the Plextor has 512K. Not sure what the Asus has, but I would expect it would be the same.
I'm thinking of switching the SATA cables, just to make sure it's not a bad cable, or even a bad SATA channel. I don't think either drive is capable of SATA 3, so the standard cables should work.

I saw a YouTube video of an experiment with CD's, and I think they had to go well beyond anything that a consumer CD reader can do in order to shatter the disc. That said, I do not believe Plextor offers its Plexi-Tools for optical discs anymore. All that I could find on their site was for SSD's - which is going to be my next investment.
I will be finished with the bulk ripping of all of my music CD's soon anyway, so the 24x I am getting from the Asus is OK. Once all of the music I enjoy (sans the "filler tracks") is on my HDD in .wav format, I won't be using the CD's themselves anymore - only for backup.

The future doesn't look good for optical discs, as Micro SD and SSD's are getting so much cheaper and more reliable, there is really no reason to continue using them. I would expect that we should be able to purchase music in uncompressed format on micro SD cards, or download it, rather than a physical disc.

The only reason I do like to still purchase CD's is so I can rip them into .wav format, instead of the compressed .m4a or .m4p or whatever iTunes uses. It seems to be less lossy than .mp3, but I still prefer the uncompressed format.