It's obvious or sounds like you have removed the M4 soc hd cap scr's from the bottom cover w/o difficulty and are now looking at the 3- retainer scr's for the tach case 
If so, you'll need a proper fitting cross-point screw driver to loosen the screws that are quite tight as Yamaha uses a compression liner on this assembly to prevent damage to the ABS tach housing. I've done this tassk in the past early on and don't recall any thd lock on these fasteners.
IMO, the solution is the proper tool using firm pressure acting against the handle while loosening!
ACE Hardware, of all places, has a nice selection of Professional grade cross-point drivers that can be identified by the dark heat treated bit end!
Good Luck
Kdub:
For those of you who have removed your tach before. How did you do it? I've got it torn down to where you can see the underside of the tach. Im struggling to remove the tiny phillips head screws on the inside. Seems they just want to strip whenever I try and turn them.