After much effort, I was able to successfully get into service mode on a Pro 2000. It took ordering a service manual for the unit, though finally the instructions above are correct, but not clear about a few things. Here's what the manual says, with my annotations:
1. Press and hold the Power button while touching Area4 (lower left) of the operation panel. (DO NOT
release the buttons.) [ Area4 is the lower left quadrant of the touch panel, not including the home/back/stop button area]
2. When the Canon logo is displayed on the operation panel, release the finger touching Area4 (lower left)
while holding the Power button, touch in order of Area2 (lower right,) Area3 (upper left,) and Area1 (upper right) of the operation panel, release the finger from Area1 (upper right) and finally release the Power button within two seconds.
[ Those are just touch/releases of area2, area3, area1 in order, followed by releasing the power buttom. It seems that from the time you release area4 until you release the power button must be less than 2 seconds]
The real confusing part of all this is that when you do all of this right, there is no immediate feedback. The system goes through its normal boot cycle and appears to have just started up as normal. However, if service mode is entered, there'll be an extra menu item, "SERVICE" at the bottom. Also, even if there was a hard error preventing normal user boot up, the system should still get to the menu if service mode is engaged.