I had hoped to access the horizontal linear encoder sensor within the print carriage of my retired Canon Pixma MX340 multi-function inkjet, but after removing the ink cartridge mounting bracket, I found no easy path to that sensor from the front. I still want to probe it in an operational state, so I'll remove the entire print carriage actuator assembly as one intact piece and possibly try again later.

The actuator assembly's main structure is a sheet of stamped sheet metal, covering the entire width of the assembly and folded into the back and upper rail for the print carriage. As expected of a key structural component, there were many attachment points.

Two self-tapping plastic screws attach directly to the injection-molded base, one left and one right. The left side (close to the motor) featured a spring-loaded mechanism. Its right side counterpart lacked this feature.

Five machine screws attach the frame to three metal brackets. Two screws to each of the large brackets on the left and right, which are in turn secured to the plastic base with more self-tapping plastic screws. I removed these two large brackets from the plastic base but decided to leave them attached to the horizontal axis actuator metal frame for several reasons: (1) in the immediate term, the serve as handles or a convenient stand allowing me to sit this actuator assembly on its back without pinching any wires or getting in the way of anything that moves. (2) in the medium term, removing them won't make accessing the linear encoder sensor any easier, and (3) in the long term, if I reuse this actuator assembly in something else, I will likely need these brackets too.

The final machine screw attached the wide metal frame to a tall metal finger rising up out of a hole in the white plastic paper tray assembly. Located width-wise between the paper printing area and the ink cartridge parking area. I'm curious if this tall finger was always planned from the start or added later in the design process when they needed more rigidity. It looks like it might be the latter.

Here's the horizontal axis removed from the plastic base. My hand is holding on to the left side bracket that I had left attached. There was a paper feed optical interrupter sensor mounted to the back of this assembly, but that could be detached and visible dangling above the large paper roller in the center of the picture above. I stuck a folded-up piece of paper in the sensor to leave it in its normal blocked state.

Electrically, there is a pair of wires to the DC motor, and three sets of flexible cable for the print head assembly. The majority of those wires are for ink cartridge communication, leaving just a few for the horizontal quadrature encoder sensor. Should I still hold out hope I could figure out those wires later?

I set the assembly down on its back on those still-attached brackets, and powered up the system. It gave me a "check ink cartridge" error which is understandable by their absence, and the startup sequence is noticeably different. But it still ran the print carriage back and forth, so I'm cautiously optimistic I haven't broken anything relating to that horizontal encoder.

I thought about continuing focus on this assembly until I could reach that horizontal encoder, but I set it aside because I found it more interesting to look at what was uncovered by its removal.

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