On a task-specific machine. Those beasts are never designed with user-maintenance in mind.
This one in particular was designed with the exterior being basically not much more than a solid box. All the exterior panels were welded together, with the exception of the back panel, which had *13* screws keeping it on. Then I had to remove another 9 screws to get the inner top panel off, and then I had to manage to unscrew the floppy drive from it's housing in a space no bigger than 4 fingers and the screwdriver bit (not the whole screwdriver, just the bit)!
And, just to make things interesting, this machine is used by the biochemistry freaks to examine DNA mapping stuff, so the *entire* work area is covered in residue from something called Ethidium Bromide, which they explain to me as a carcenogenic mutagen that I would do well to keep from getting on me if I hope to ever have kids. And while the ensure me that the trace ammounts of residue that are on the equipment are not enough to actually cause problems, they still insist that I wear gloves and a lab coat to keep from getting any on my skin or clothes (which can then later get it onto my skin) and they advise me to wash off any tools I take down there with me. Just for safty, of course.
So, what would probably only have taken 30 mintues or so (it was tough figureing out how that machine went together) turned into a 2 hour job with me trying not to bump my head (which was uncovered) against any of the panels as I was poking my head into the innards of the box or against the various cords dangling around while I was twisting and turning to get as many fingers as possible on the bloody screws.
I love my job, every day a different, exciting, possibly life-threatenig, adventure! :)