Pins to power to test CD/radio? How to eject a disc?

So, a few months ago the CD player/radio unit on my 2010 Prius started giving me problems. One day it just was completely dead (not only no sound, no symbols at all on the LCD either), then a few days later it came back, then went again, and eventually just finally died. I checked all the fuses, and they were good.

The used car dealer where I'd bought the car from less than a year ago got me an excellent deal online on another used unit, and installed it at no charge, which was great. They said they didn't see anything on the outside that could have explained why it died, so they assumed that it was internal to the unit. However, one day about a week ago (and only a few weeks after it was installed), the new unit suddenly didn't function for a few hours, which at least raised the possibility that the problem was actually in the car itself, though since then it's been fine.

I had the dealer give me back the old unit after putting the new one in, since they said it would just go to waste rather than them being able to send it to anyone who could fix it. I thought it might be a fun electronics project to open it up and see if I could find anything that might be the problem. Even if I didn't, I could take out the laser diode, any interesting motors, etc. Now that the new one acted up also at least once, however, I'm a bit leery to open it in such a manner that I couldn't reassemble it, in case it would ever need to be put back in.

First thing--there was a CD in the player when it died, which I couldn't eject, and I'd like to get it out. While some parts of the unit are easily disassembled (the black front piece with the buttons and knobs came off with just removing two screws and lifting some plastic tabs), the CD player seems to be its own sealed unit, held together not just by screws but also by folded metal tabs that would need to be pried up. Once this is done, pushing them back down looks like it would be a pain. So it would be great to be able to get the disc out without opening this casing. With the black front off you can see the edge of the disc, but there are metal tabs blocking its way out and the spindle is through the hole. The former are rather easy to push out of the way with a screwdriver, the latter not so. You would think that there would be something much like the "paperclip hole" on CD-ROMs that would allow you to release the spindle by inserting a screwdriver in or something, but I don't see one.

Also, in the process of looking at this, I was trying to power the unit up to see if I could then press the eject button. Oddly, the shop didn't unplug the plugs from the sockets on the old unit and plug them into the new one, rather they cut the wires, leaving short lengths of wire attached to the plugs. This has the fortunate side effect of the color coding being intact. Looking at the wiring references I saw linked on this forum and elsewhere, it looks like the red and black wires in the connector with the fewest pins (and thickest wires) are + and - power (12V), as expected, and that the yellow also has positive power when the car turns on. I stripped them and tried connecting the black wire to the cathode of a 9V battery and the red and yellow to the anode, hoping that despite the 25% undervoltage, that the circuits inside could regulate that down to what the microcontroller chip inside needs to boot, but nothing at all appeared on the LCD when I pressed the power button.

It's quite possible that it really does need 12V, and a 12V DC power supply might be a good investment anyway, but it's also possible that the unit is simply dead, or that more than just those three terminals need to be powered for it to boot up even if it's working. I'm amazed at just how many wires it has--far more than a typical home stereo system, DVD player, etc. has--I'm assuming many of them allow for other systems in the car to issue commands to the unit to change the volume, station, etc. if those features are enabled. In any case, if I knew what the minimum is for a good unit to power up (in the sense of showing something on the LCD, not playing actual sound through the now non-existent speakers), that would first help me tell if the unit is truly dead. If it was, then I wouldn't feel bad about further disassembling it. Secondly, if I were to find a broken connection inside and were to re-solder it, I could then tell if I'd actually fixed it.

So, what terminals need to be powered at what voltage for the unit to turn on? and is there an easy way to release a stuck disc in a unit that won't turn on?

I have no experience at all working on anything whatsoever to do with cars, but a long history of opening up and fiddling with all sorts of other electronics, starting with cassette players and VCRs in the early 90s up to computers and other digital devices later. In fact, that's half the reason I asked for the radio back. As I kid I used to ask for broken gadgets to take apart for Christmas, so I thought opening this one up now would be worth it for the nostalgia value.