Troubleshooting a Mac CD tray that won’t stay closed

Recently, I placed my Mac Pro up for sale, both on the net in general and on eBay. The eBay auction closed with a successful bidder, so yesterday, I went to prep the machine for shipping. After wiping the drives and reinstalling OS X, I had but one thing to do: solve a small but annoying problem with one of the two installed disc burning SuperDrives (name used for simplification; one was an actual SuperDrive from Apple; the other a multi-format burning drive from Sony).

The stock drive, which I had mounted in the lower slot, worked fine. So did the after-market upper drive, as long as there was a disc in the slot. If I ejected the disc and then closed the tray, the drive would grind for a few seconds, then eject. It would then stay ejected for a few minutes, until (I believe) OS X noticed it was open. It would then close, and the grind-eject cycle would repeat.

I'm posting the sordid details of my experience in case anyone else is looking for help with a CD/DVD tray that won't stay closed on their own OS X machine; perhaps it'll show up in a Google Mac-specific search at some point in the future. Read on for the details…

I figured it was a simple matter of a dust in the innards or something, so I shut down the Mac Pro, removed the drives, disassembled the case on the troublesome drive, and cleaned it out. After putting everything back together, nothing had changed: the upper drive would auto-eject, the lower one would not. I then Googled for the problem, and didn't find anything specific to the problem on Macs that looked like it would help. There were a lot of discussions about such issues on Windows PCs, however.

Now I suspected some sort of subtle drive failure, so I drove to a local PC parts place and picked up a $25 generic burner. Returned home, swapped out the bad drive, reassembled…and nothing had changed. The brand-new drive was now exhibiting the exact same behavior.

I disassembled the Mac Pro again, and this time, swapped the two drives around, so that the "good" stock drive was in the upper bay, and the new "bad" drive was in the lower bay. (As these are IDE drives, I also switched the master/slave jumpers on each drive.) Upon reboot, the upper drive—the previously "good" one—now had the auto-eject issue. Argh!

I then removed the "bad" drive completely, leaving the "good" drive in the lower bay. No auto-eject issues. I then moved it to the upper bay, and bingo, it started auto-ejecting. This seemed to imply some sort of cabling issue, so I spent a few reboots trying various combinations of master, slave, and cable select jumper settings. Nothing worked: whichever drive was connected in the upper slot would auto-eject, and it didn't matter if there were one or two drives connected.

I also tried resetting parameter RAM (no luck), booting in single user mode (nothing interesting), and examining the log fles (no entries at all). Desperate for help at this point, I returned to Google, and started browsing the Windows-related threads on the issue. One contained an unlikely fix, but I was willing to try almost anything at this point.

I connected both drives, booted up, and let the upper drive do its auto-eject thing. This time, though, I didn't fully reassemble the Mac Pro. I left both drives simply sitting on their shelf, poking out the side of the Mac Pro. When the "upper" drive did its auto-eject thing, I pushed it back in, and then, as the grinding noise started, I poked a straightened paperclip into the tiny hole that's used to manually eject a stuck CD/DVD. (You can't reach this hole if the drive is installed in the Mac Pro, as the bezel hides it.)

After the tray manually opened, I pushed it closed. Amazingly, the grinding noise was gone, and the tray stayed in! I then shut down and rebooted…and it worked perfectly. It continued to work even after I swapped the other two drives into the "upper" position, and changed the "lower" drive as well. Very weird.

Now, I'm completely stumped as to why this fix worked: remember that I'd tried a total of three drives in the upper position, so it clearly wasn't something related to any particular drive. It also can't be related to OS X, as I'd fully wiped the drive and reinstalled a clean copy of OS X just hours earlier. And I don't see how it can be related to the cabling, because it seems unlikely to me that the manual eject hole is connected to any circuitry. So I have no idea why this worked, I'm just thrilled it did work after several frustrating hours of troubleshooting.

If you have any ideas as to why this may have worked, I'd love to hear them.