Sorry for the delayed response. I've been getting ready to change jobs. Now that is done with but Christmas still awaits so time is limited.
We've already tried resetting PRAM and the SMC, so moving on from there:
I know for certain that the drives are rotating the media at least a small distance--when ejecting media, it isn't in the same rotational position as when I loaded it. It's hard to be absolutely certain that they spin any more than that, but I suspect they do.
Using system's original Superdrive (third party Blu-ray disconnected):
- Can't boot from this system's original distribution DVD (Leopard 10.5.6). Like any media I try in this drive, the drive makes some noises and the tray opens up.
- After boot from hard disk (10.9) it can't access any type of media--blank, factory pressed, or burned at home. No matter what I load, the drive just unloads after making some noises.
With just the Blu-ray connected (Superdrive disconnected), the only thing different is that the drive doesn't unload automatically.
In Toast Titanium 11's Recorder Settings window you can watch the media-loaded status of a drive. The sequence is the same for either drive:
- Tray open --> "Status: No Disc"
- Insert media, close tray --> "Status: Waiting..."
- Some sounds from drive, then --> "Status: No Disc"
- (SuperDrive only) Tray automatically reopens
Last of all, (with power off) I unplugged the Blu-ray's SATA cable and connected one from a loose SATA hard drive.
This drive works normally!
Whatever's wrong, perhaps it has something to do with optical disc media sensing. Since the problem appeared to start with Mountain Lion and affects both drives, software would seem the most likely cause--
except that it can't boot from distribution media.
The only caveat to that is that I hadn't used either of the drives for two or three weeks before installing 10.9. Still, it seems unlikely for them both to develop the same problem at the same time.