This will be of rather limited interest; but I failed to find the information on the web when I needed it, and when I figured it out myself (which turned out not to be hard) I made a note to perpetuate the information, as it were.
So. Had definite haze on the inside of the glass on the bed of Oleg’s old Scanmaker 4, needed to clean it. The question is, how to get at the glass? Turns out the scanner is designed to make this easy, though it wasn’t completely obvious to me at first glance.
First, we take off the lid. The “hinge” is very clever—solid molded parts on the lid fit into molded holes in the plastic case, ending up being quite a good hinge.
The round holes at the outside of the base are where these bits come out (and go back in later).
You need to open the top slightly more than straight up, and then lift it straight up. Fiddling with angles slightly helps the hinge thingies come out of the holes.
And with a little fiddling the lid comes off very nicely.
Now we turn our attention to the center hole. Turns out there’s a springy plastic bit at the bottom of that hole which, when pushed down, releases the top plate to slide back about half an inch.
Cleverly, it’s somewhat too small for many fingers (certainly for mine). However, a somewhat skinny pen does the trick nicely (a screwdriver would work fine too).
Really the pen should go in straight down. And a skinnier pen would work better. You have to press a bit harder than seems obvious, and there’s no clear indication by feel on the pushing pen when it’s enough. But, when it’s enough, you can slide the top plate (with the glass in it) back about half an inch.
(Shown at the front left corner).
At this point you can lift the top late, with the glass, straight up and it comes right off. It’s moderately heavy, that’s a solid sheet of glass in there.
And now you can turn it over, clean it, do other stuff inside if you can think of anything.
To reassemble, put the top plate on in the position you lifted it from, and it should drop right down into place. Then slide it forward, and it’ll lock in. Finally, put the lid back on (hold it vertical or slightly past, put the balls into the holes, wiggle cleverly until it drops down pretty easily, and then it will close normally).
When I finally looked closely at the scanner, I figured this out in about a minute, so maybe nobody really needs this. But I searched for info on how to do this first, and if I’d found instructions it would have saved me a bit of time before I just started looking for things to push, slide, or unscrew.