phaser 7760 w/ no image

replaced all imaging units (except black) printed few hundres sheets then NO Image! it prints magenta and black but only about 1" - 2" wide from leading edge all the way down to trail towards the front of the printer (mostly magenta only). checked acumulater belt unit and found small piece (dime size) torn off from the belt (towards the back of the printer) i even taped back the small piece with scotch tape but didn't fix the prob. could this have cause the image problem? where is the laser unit? could the laser path be blocked by toner that needs cleaning?
any help would be greatly appreciated

jim