There's one final sensor I'm trying to access as I tear down my old Canon Pixma MX340 multi-function inkjet: its print carriage linear quadrature encoder. Removing the lower rail allowed the print carriage to slide free, but I first tried to see if I can keep it on the rail. I was afraid sliding it off the rail would unpredictably release the spring-loaded tension mechanisms I can partially see. (White plastic below the belt and behind sheet metal in picture below.)

Without sliding it off the rail, I could access the two fasteners I couldn't access before. Removing them allowed two separate pieces of black plastic to move apart slightly, but they were both within the lower rail. The carriage has to slide off before I could pull those pieces apart.

As I slid the carriage off the lower rail, my fear came to pass: I heard a "pling" announcing a spring departing to seek new adventures. Its former home highlighted in red on the left, and its companion still in place on the right. Thankfully I managed to find this spring later, because every spring I lose decreases the odds I can repurpose the entire print carriage assembly intact for a future project.

Carefully setting down the rear cover with its many springs, I could see inside the carriage. Front and center is the encoder sensor, but its pins go through the circuit board to the other side. The flexible ribbon cables are also connected on the other side. I will have to remove four more screws before I can see how they are wired.

The flex cable connectors were expected, as are the ink cartridge contacts. The surprise on the front is a pair of electrolytic capacitors. I guess inkjet cartridges need small bursts of buffered power to do their thing.

I wasn't interested in reverse-engineering the ink cartridge interface, but I was interested in how the electrical contacts are implemented. Each contact is a thin spring-loaded metal blade. (My thumb nail is pushing on one.) Unfortunately, it appears if I want to see more I would have to remove the contact assembly from the circuit board. I haven't had a great success rate unsoldering components with this many pins, so I will save my unsoldering practice session for later. Right now I'm staying focused on the optical encoder sensor.

This teardown ran far longer than I originally thought it would. Click here to rewind back to where this adventure started.