Feature image from Amazon.com

Study subject: EPSON LX-300+ dot matrix printer

Take apart time: 2025/1/16 and 2025/1/26, 2.5 hours

Group members: Wen-Yi, Yifan, Xinyin (Sing)

Dot matrix printers print characters and patterns in dots (Fig. 1).

Figure 1. Characters printed using a dot matrix printer.

With no prior knowledge about dot matrix printers, Wen-Yi, Yifan, and Sing (I) took apart an EPSON LX-300+ dot matrix printer to understand its design and manufacture process.

The printer we received is mostly contact. We noticed that the top cover shown in the Amazon picture and the ink ribbon were missing (feature image). We reason that the top cover is designed to be able to easily take apart so that the user can replace the ink ribbon, tackle the paper jam issue, and clean the paper rollers. Additionally, according to the user manual on Amazon, the paper supports and the paper feed knob are installed by the users (Fig. 2).

The remainder of the printer is held together by 42 screws (spreadsheet – Materials) and snap joints (Fig. 3). We reason that the printer is not designed to be frequently taken apart by users. However, it is straightforward to dissemble the shells of the printer by taking off the screws, if the printer needs to be fixed.

Figure 2. An EPSON LX-300+ dot matrix printer without the top cover and the ink ribbon.

Figure 3. Snap joints in circles.

The principle we followed in disassembly is to disassemble the most accessible and easiest parts before the tricky parts and to take apart the bigger parts before dissecting them into smaller units.

First, we lifted and took off the paper guide to be dissembled later (Fig. 4).

Figure 4. Paper guide.

Next, we examined the printhead and the carriage belt. The printhead moves on a metal rod, and its motion is synchronized with the carriage belt (Video 1). When the printer is working, the printhead moves back and forth and hits the ribbon with a needle to transfer the ink to the paper (Video 2).

Video 1. Printhead movement.

Video 2. EPSON LX-300+ dot matrix printer using ESC/P on Windows 11.

The printhead is attached to a cable (Fig. 5), which connects it to the motherboard. We were unable to further break down the printhead.

Figure 5. Printhead with the cable. 

Then, we loosen the screws with big and medium screwdrivers and a magnetic screwdriver to take off the upper plastic shell with letters and logos (Fig. 6).

Figure 6. Upper plastic shell on the right separated from the remainder of the printer.

We further loosened the screws and separating the remainder into two parts. The top part is composed of metal sheets with paper rollers, carriage belt, and other components. The bottom part is composed of a plastic shell and a metal sheet with motherboards (Fig. 7).

Figure 7. The top part and the bottom part.

On the top part behind the paper feed shaft (Fig. 6), we found a stepper motor, which functions to control the movement of paper (Fig. 8). The inside of stepper motor has copper windings, which convert electricity into rotation (Video 3). 

Figure 8. Stepper motor.

Video 3. Stepper Motor – Operating Principle – Nanotec

We turned the top part to the front side, took off the gears, and consequently the paper feed shaft. The white gear was attached to the black plastic piece via snap-fit. Dr. Wettergreen tried to push the protruded black part in and pull the white gear out. However, we failed to pull it out that way, so we broke the protruded part to take the gear out.

Figure 9. Gears and paper feed shaft. The snap-fit is indicated by the red circle.

That concludes the first day of our taking apart lab. Below is a picture of our cleaned table (Fig. 10).

Figure 10. Table cleaned on 2025/1/16.

On our second day of taking apart, we continued to dissemble the top part. We pulled off the black plastic piece that held the gears (Fig. 11).  The piece was attached to the metal sheet via snap joints.

Figure 11. Take off the black plastic piece that was attached to the metal sheet via snap joints.

Then, we took off the black plastic piece that held the rod for the printhead (Fig. 12 left), and a rod next to springs. Given that the rod is beneath the paper feed shaft, we hypothesize that it functioned to control the speed of the paper.

Figure 12. Left: rod for the printhead and the black piece. Right: rod and springs.

The top part was fully dissembled.

Next, we dissembled the paper guide. It has two pieces of plastic shells, two paper supports, and a paper feed roller composed of a long metal rod and four rubber pieces.

Figure 13. Left: the opened paper guide; middle: one of the paper supports; right: the paper feed roller.

For the bottom part, we first pulled out the switch that fits on the plastic shell (Fig. 14).

Figure 14. The switch.

Then, we unplugged the adaptors and wires and took off the motherboards from the metal sheet (Fig. 15). A mushroom-shaped thing (Fig. 16) held the metal sheet, the motherboard in Fig. 15 left, and the plastic shell tightly. We did not know what it was. We failed to remove it at first and broke the corner of the motherboard.

Figure 15. Motherboards.

Finally, only the metal piece attached to the plastic shell needed to be disassembled. We tried to use a flat-head screwdriver to pry the mushroom thing open, but it did not work. We thought it was a screw, so we used a plier to bite the mushroom head tightly while turning the board. Finally, the screw was pulled out (Fig. 16). The screw was so tight and was the hardest part of our dissembling process.

Figure 16. The mushroom-shaped screw held by a plier.

After the dissembly, we sorted the parts based on materials, functions, and similarities in shapes. The weights of each group are shown below and also in the spreadsheet – Materials. The major components of the printer are plastic and metals. The outermost plastic components make up the most weight, about 28%. The thickness of the plastic shell and the layer of metal sheets protect the delicate inside of the printer. The delicate core components, including motherboards, wires, the printhead, and the stepper motor, accounted for about 17% of the total weight. We find it interesting that the printer has many snap joints and screws as many as 42 to hold lots of components together. The screws and possibly the carriage belt and gears were made off-the-shelf. In contrast, other components such as plastic shells, metal sheets, the printhead, rollers, and motherboards are likely to be uniquely made for this type of device. Most of the components can be recycled. The ink ribbon, which was not present in our printer, would be the most harmful. According to Cohen recycling, the ink and toner cartridges are the only components that cannot be recycled by them.

Figure 17. Components of the Epson lx-300+dot matrix printer organized in groups.

Taking apart the Epson lx-300+dot matrix printer gives me a deep appreciation of the intricacy beneath the simple exterior of the printer. From hypothesizing, discussing with my group members, and searching the functions of each component, I gained a clearer understanding of how the printhead, carriage belt, and gears work together, how the paper guide and the rollers facilitate paper movement, and the physics behind the stepper motor.

I am really impressed by how the designers compactly assembled components so that the device is easy to move around and does not cost too much plastic and metals. The 42 screws give the printer durability but also make it labor-intensive to dissemble it. One of the most awe-inspiring moments was holding the motherboards in my hands. They are art—beautiful, intricate, and mysterious. I am moved by the human ingenuity gathered in this little device.

Finally, this experience fulfilled my childhood dream. As a toddler, I had an irresistible curiosity to explore intricate objects with small components, rather than play with stuffed animals. Yet, those fascinating objects were always kept out of my reach. This teardown lab granted the wish of my 2-year-old self—the chance to finally take apart something complex, to understand how it works. I am grateful for the collaboration with my friends and for the opportunity to exercise our creativity and sharpen our observation and problem-solving skills. Thank you!

Below is a picture of our cleaned table (Fig. 18).

Figure 18. Table cleaned on 2025/1/26.

Worksheets:
1. Three components and design features. 
2. Spreadsheets about materials and tools.