Specifically, the inside (or bottom) of the main glass. Because, as anybody who has used a scanner critically knows, the inside of those things out-gases (from the plastic) and deposits thin layers of gunk on the bottom of the glass.
You do also have to clean the top of the glass, but that’s easy; normal glass or lens cleaning techniques (so, Windex, water and ammonia, alcohol-based lens cleaner, with suitable soft cloth or paper).
Ammonia, in your own mix or in Windex, is corrosive to electronics, so be careful what you spray around where!
It’s easy to Google up posts all over about the process in general, like here.
The bottom of the glass is no harder—once you get to it.
The basic process is:
- Unplug everything
- Remove the scanning lid and set it carefully aside
- Remove the four plastic plugs over the screws that hold the top on
- Remove the screws that hold the top on (small Phillips)
- Lift off the top
- Clean the bottom of the glass, as above
The problem is those little plugs. Well, they’re not actually that big a problem, but it’s not obvious from the outside how to do this.
If your scanner is out of warranty, it doesn’t matter too much; the failure mode is gashing up the plugs and the top of the housing, which are purely cosmetic issues. If however your scanner is still in warranty, clear evidence that you’ve been inside could void your warranty.
So, here’s one of the plugs, in place:
Those scratches were made by me, with a small (jeweler’s) flat-blade screwdriver, trying to find the point to pry the plug out. Ruined the screwdriver, too, by the way, but this was one of the vestigial ones from an old set and I was rather expecting that, using such a small thing as a pry-bar.
There is, it turns out, a better way! (This is my shocked face.)
Note the wide “V” on the plastic cap. With the scanner on the desk in front of you so that the top opens away from you (I think of this as the “normal” position to use a flatbed scanner in), that “V” is pointing down (meaning the wide side is away from me).
Here’s the cap off, and what a cap looks like from the bottom:
Note the top cap is well and truly messed up; that’s the first one I got out, before I knew how to do it reasonably cleanly.
Now, look at the bottom cap (also oriented so the bottom of the “V” is towards us, wide end away). See that big gap at the top? Yeah, turns out if you pry there it’s much easier to get the pry-bar in and much easier to get the cap out, doing almost no damage. Not none, if you’re in warranty you should still think about that. I tried the “duct tape” thing frequently cited on the web, but it did nothing at all with mine.
So: Put your narrow pry-bar in at the wide part of the “V”, and pry there. Comes right off!
There’s something slightly weird about the front left corner, that was the hardest bit to get off and get on. I found the top went on much better if you put the left side down first.
But my glass is all much cleaner now.