URL: http://www.youtube.com/watch?v=kvFMFb9JylQ (EOS 50D)
URL: http://www.youtube.com/watch?v=O3cCTv7JbrY (EOS 1000D)
The procedures are shown clearly and it is carried out in a professional manner.
Besides, there is a guide for how to check and try to repair a Pentax MZ film body that had its mirror locked up in the following thread:-
http://forum.xitek.com/forum-redirect-goto-findpost-ptid-1125971-pid-46046531.html
(in Chinese)
The mirror locked up issue is actually a common issue amongst those MZ bodies, which would show up after some years of use, including mine. I shall try to open the bottom of my locked MZ to check and do it myself later, when I have the time. These cameras are not supported by my local Pentax service centre anyway, I bet. Their usual excuse was that "the body was discontinued for more than ten years ago and the required spare part is not available anymore."! >:-(