Okay, so I recently brought an untested Mega CD model 1. The AC adaptor adaptor for it finally arrived today, so I've been able to take a closer look at it. It starts up no problems, but it won't eject the tray. It makes a bit of noise, but that's all. I've pulled it apart and it looks like everything is in order, those two little switches seem to be getting hit at the right time (one when the tray is open, and the other when it's closed). The little plastic tabs that hold the board haven't snapped, the board is firmly in place.
One thing I've noticed is the tray seems to stick when it's almost closed/open. If you give the tray a little pull while it's trying to open, it's able to fully open (though it also won't fully close by itself, it seems to get stuck in the same position when closing and even if you give it some assistance, it still won't raise the spindle when the tray is pushed shut). I've been fiddling with the tray, and there seems to be a little resistance when the tray is almost closed, like some kind of friction, though I've tried adding lubricant to different surfaces, and it doesn't seem to have helped.
Little help guys? :D