Hi
I had a similar problem on my CD 5500, it was too eager to close itself, timed it to around 20 sec or so before it closed itself, see this topic:
http://forum.beoworld.org/forums/thread/67637.aspx
With help of servicemanual on site i opend the case, raised the "mainboard" and even folded down the front panel of the CD-player. The only switch i could visable see was the one in the middle of case (just under the thread that drags the cd-tray). I did nothing more then just touched it abit (of corse w/o any power on hehe) too see that it "looked ok". After that i closed it all and thought i hadnt mended anything but when i started using it again it now works flawlessly.
On servicemanulas first page the swtich is called 90S1 (section 1-1)
Hope that might help
MoglesMac
Sweden