Ghosted – When and how to clean an Epson 4990 transparency unit

I’ve had my Epson 4990 since the model was new, so the best part of two decades. It has always served me surprisingly well, although it’s now old enough (by far!) to occasionally require a little TLC. In particular, it can do with a little dusting once in a while.

Case in point, consider the crop of a 35mm scan below:

That’s a pretty bad case of measles alright. Here’s another one:

It’s slightly more subtle in the bottom image, but it’s still more than annoying. Now, these are my equivalents to a contact print, so I don’t mind the occasional bit of dust. But it does limit the usefulness of these scans, and besides, the solution is quite simple.

Note the pattern match between both examples above:

That’s a pretty clear sign that the defect is rally on the scanner, somehow.

Also note that dust specs on (flatbed) scans tend to come in various degrees of fuzziness:

The fuzzy ball on the left is what I’m addressing in this blog. The wire-like thing in the middle is a piece of lint and if it shows up as sharply imaged as here, it’s usually on the surface of the film. The tiny speck on the right is similarly a tiny flake of debris, usually on the film surface.

The degree of fuzziness relates to how far the dust is removed from the plane of sharp focus of the scanner. Flatbed scanners have a depth of focus that’s limited to a millimeter or so, and anything beyond that will become increasingly fuzzy. This is good news for the most part, since tiny specks of dust like the one on the right will only be a problem if they’re on the actual film itself. If it’s on either of the glass plates, it likely won’t even show up.

“Either” of the glass plates? Yes, keep in mind that a flatbed scanner like the Epson 4990 (but also its successors like the V700 etc.) have a glass platen on which the film sits (in a holder, typically) and a plate of glass above the film with the light source above it (the transparency unit). Two glass plates makes for four surfaces that dust can settle on. If a scanner is reasonably new and used in a reasonably clean environment, it’s mostly the top side of the bed-glass that needs to be wiped clean once in a while.

However, as time goes by and the scanner is maybe moved around, kept in storage for a while and goes through the regular tribulations of a scanner’s life, dust and debris will start to find its way to the other three surfaces as well. At that point, both sides of both glass plates will have to be cleaned from time to time. And this time it was definitely time for the upper glass plate that’s part of the transparency unit to be wiped down, as evidenced by this pretty arrangement of ghostly apparitions:

Oops.

Removing the transparency unit is as simple as disconnecting its cable from the main unit and lifting the lid off.

Unplug the white cable from the bottom unit, then lift off the lid/transparency unit.

Here’s the unit as viewed from its underside, looking at the (to be cleaned) glass plate:

Note the five screws that hold the glass plate assembly, marked in red above. Unscrew these and us a flat-head screwdriver to pry open the lid by the eight slots (3 top, 3 down, 2 to the right; marked in yellow) where the plastic & glass assembly snaps into the outer shell of the lid.

The glass assembly can now be lifted away to be cleaned on both sides. This photo shows the glass assembly turned over to show the top-side of the glass:

This top side is in fact the problem side in my experience. White dust tends to collect here in one or two clusters, fairly close to each other. The source appears to be the white diffusor material that’s used for the light source, which can be seen as the two vertical white bars in the photo below, which shows the transparency unit with the glass assembly removed.

Here’s a closer-up of that section:

It’s also possible that the curved connector cable (shown as an irregular arc on the previous image) sheds some debris as it moves. Either way, it’s the materials used in the construction that over time become slightly brittle and helped by the movements of the lid and light source carriage throws down some dust.

Cleaning the glass is as simple as wiping it off with a lint-free cloth – just make sure it has absolutely no dust/sand or any sharp (metal) fibers embedded in it, somehow. You don’t want to scratch this glass as it’s probably somewhat difficult to replace. I usually spray some ethanol onto the glass to rub off anything that doesn’t clean off by dry wiping, although this is mostly applicable for the glass surfaces that are exposed in normal operation to sticky fingers.

While I was in here, I snapped some images of the inside of the transparency unit; they might be useful for posterity – who knows!?

Looking from where the glass platen sits towards the moving light source carriage. Part of the power supply is visible on the left, below the serial number sticker. There’s a small control PCB just to the right. The red drive belt and smooth metal guide are visible in the extreme left of the image. The white flat cable sticking out into the foreground is apparently used for light source control and power. Note the ‘gutter’ in the center of the image which is the fancy progress indicator visible from the top of the lid as the scanner is being used; a blue LED mounted on the light source carriage shines through this.
Here’s something that actually surprised me. This is an older type scanner and back in those days, illumination of the sample was done with a narrow strip fluorescent tube. I’d have to check to make sure, but I think this is how the 4990 also illuminates reflective media (paper). However, I was surprised to see that for the transparency unit, white LEDs are actually used – I never realized this! Note the strip of LEDs mounted in the center of the image, ‘shining’ towards the camera. The light bounces against a reflector and then bounces back into the white gutter behind the LEDs. This indirect lighting system is the diffusor that ensures even illumination. Smart!

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