It was fun to look over the automatic document feeder (ADF) in this Canon Pixma MX340 multifunction inkjet. Thanks to clever mechanical design, it only needed two sensors and a single motor to feed a stack of paper through the scanner one sheet at a time. After removing those components I was faced with the hinge mechanism holding the ADF (and control panel) up above the scanner bed.

In addition to normal hinge rotation, these hinge modules can move vertically extending upwards by about 3cm. This accommodates thicker material on the scanner bed, such as a book. Some kind of a mechanical stop prevents them from being pulled out more than that 3cm. Not falling apart during normal use is great, but now that stop mechanism is an obstacle blocking progress in my teardown.

After removing the control panel and ADF, I have a large tray and two hinge modules, each held by three fasteners.

Removing the fasteners freed the module from the tray. And while that gives a bit of play moving the module around, the top part is physically too large to fit through the tray slot. The hinge module has to be removed from the scanner bed below, but I couldn't see what's still holding it place because the tray is still in the way. The teardown so far tells me Canon engineers must have designed for graceful and non-destructive removal, but my belief didn't lead to useful insight. Fingertip tactile feedback tells me there's some sort of mechanical interaction down there, but I couldn't see it to understand what I'm feeling.

Conceding defeat, I went with the brute-force mechanism and pried one hinge assembly loose. This damaged its vertical channel. Once removed, I could see how things worked: a small tab held the hinge module in a vertical channel. This channel is blocked on top to keep the hinge from falling out during normal use.

As long as the tab stayed in the channel, the hinge module stayed inside. However, there was a small slot in the side of the channel around halfway up. To remove this hinge module non-destructively, we have to slide it sideways into that alternate channel.

This sideways movement was not allowed until the three fasteners holding the hinge mechanism to the tray were removed. But given that little bit of mechanical play, we can move the tab into the alternate channel. It is not blocked at the top, allowing the hinge module to slide out. Those Canon mechanical engineers were sure clever, too clever for me to figure out their trickery on this first pass. Maybe I'll encounter a similar mechanism in the future, but it won't be in this teardown. The next hinge down is for the scanner bed module, and it's completely different.

This teardown ran far longer than I originally thought it would. Click here for the starting point.