I might be able to make a comment that makes some sense to you.
I have owned several CD changers, including ones made by Yamaha.
What happens is that the belts that control the opening and closing of
the tray and engage various features tend to stretch over a period of years.
Thus you get things, like the drawer doesn't go out or in properly. Or some
other weird thing happens. The best suggestion I have, if you feel confident is
do the following procedure for locating a slipping belt.
1 Unplug the power from unit
2 Remove the cover (usually a phillips head screwdriver will work.
3 Plug in the unit, push the power button but don't
reach inside of it.
4 With a good, bright flashlight so you see very well push the button to open the door.
While it is trying to open, LOOK for a small pulley attached to a belt that is attempting
unsuccessfully to open the door. That belt will look good, but be stretched enough to not
succeed. It will take some repeating to (hopefully) find it.
5 Replace that belt.
The best way to do this is to remove it and locate and electronic PARTS supplier in your area.
Not really Radio Shack but a true electronic parts place where you can go down and the counter person will help you match it up to belts that they stock for thousands of small electronics devices. Might take a lot of searching.
There is one other solution I know of. VERY OFTEN these devices like your CD Changer end up in thrift stores all across America. They can now be bought for a song, so to speak.
I hope this helps you,
P.S. Here is a link to download your owner's manual.http://usa.yamaha.com/products/audio-visual/hifi-components/cd-players/cdc-765_black__u/?mode=model