Problem solved. I found the 848 service manual (in the second post THANKS)... Take the top cover off (velcroed on at bottom requires more of a pull than you may want to do).. Pull the bottom out and slide the cover up... There is another flat cover behind that, grab it at the top of the machine and slide straight up. with the loading door on the front open. Turn it on.... Once it boots up, you can look straight down and see the light. Visible dust swab with lens cleaners and wipe across it.... Then you can do the lens which you will see in front of you.
Works great. If you do a lot of scans, you need to clean it maybe every 400-600. Takes about 3 minutes once you do it the first time.
THANKS
Mark