I have noticed that on older desktop PCs the CD/DVD drive tray 99 times out of 100 will be stuck and won’t open. In some cases I could open it manually, with the aid of a straightened paperclip inside the hole. But sometimes it is frozen solidly and even the paperclip won’t help.
This invariably happens on computers where the optical drive isn’t used frequently. But why? Is it due to degradation of the plastic gears of the tray opening mechanism?
The most common cause is that the drive was trying to close with a disc not yet set in the tray right. As it closes, the disc jams causing the internal gearing to jump. Other abuses like yanking on the tray, etc. also cause problems.
It may work, with some insert/eject retries after that. But eventually the user gets tired of it and stops using it. Later, when it’s used again, it just plain doesn’t work anymore.
The standard sequence for tray-based drives is that the tray gets pulled in, once the tray is nearly all the way in, the spindle is lifted up to push into the center of the disc, then a “locking” occurs: a little extra shove into a stable position.
The timing of these events is critical. If they get off then the loading fails, if the locked position is not detected in the right time frame, the drive reverses things and ejects the tray.
If the system gets in a weird state with the gearing, it may get confused as to whether there is a disc in or not, whether it is locked or not, etc. It may also not be able to get out of the lock position on it’s own. Then the paperclip comes out. But usually the gears being out of kilter persists and the problem recurs.
Stripped gears can happen (plastic, of course), but that takes some real abuse to occur.
Slot systems are even trickier since a lot more of it is based on detecting whether a disc is inserted and how far.
I have many times taken apart a optical drive to try and realign things. Sometimes I can, sometimes not. It’s not all that easy to do.
Cheap mechanism with little durability and needing high precision to work right. You have to consider optical drives a disposable part of computers, both for the tray mechanism and the read/write mechanism.