How to Remove and Reinstall the Epson ET-8550 Printer Carriage Assembly

The Epson ET-8550 is a powerful photo printer, but like many advanced inkjet printers, it contains a complex carriage system with several moving parts, sensors, cables, springs, gears, and alignment components. When the printer develops a carriage-related issue, a technician may need to remove the printer carriage to inspect the CR motor, CR encoder strip, CR PW cable, PW sensor, APG mechanism, cam holder, transmission slider, or related parts.

This repair requires patience and careful organization. Several parts look similar, and some components rely on spring tension or gear positioning. Therefore, it is important to understand not only how to remove the carriage, but also how the surrounding mechanisms work together.

This article explains the carriage removal process for the Epson ET-8550 and provides practical installation tips. It is written as a step-by-step technical guide for repair shops, DIY printer repair users, and technicians who want to understand the carriage assembly before taking it apart. We also have a video below to show how it's done, which can help you see the part locations, movement, and hand positioning during the repair.

Understanding the Epson ET-8550 Carriage System

The printer carriage is the moving assembly that carries the printhead across the paper path. During printing, the carriage travels left and right while the paper advances underneath it. Because the ET-8550 prints with precision, the carriage system depends on several sensors and mechanical parts working together.

The CR motor drives the carriage movement through a belt. The CR encoder strip tells the printer where the carriage is located. The CR encoder reader reads that strip as the carriage moves. The CR PW cable connects carriage electronics to the printer's main system. The PW sensor helps detect paper width and positioning. Meanwhile, the APG mechanism adjusts the printhead height relative to the paper surface.

In addition, the ET-8550 uses a transmission slider, change lever, cam holder, spring, rod, gear, and related components to control certain mechanical movements. These parts may look intimidating at first, but they make more sense once you see how each one moves.

Before removing the carriage, take pictures from several angles. Also, organize screws by section. Since the printer uses different screw sizes and brackets, mixing hardware can slow down reassembly or cause damage.

Using Parts Resources Before Starting

Before beginning the repair, it helps to identify the parts with a diagram. BCH Technologies provides resources that can help locate ET-8550 components. You can visit bchtechnologies.com and search for the ET8550 parts list. A parts list can help you identify the CR encoder strip, CR motor, cam holder, transmission slider, carriage assembly, PW sensor, CR PW cable, and other parts.

A visual parts reference becomes especially helpful when working on a printer carriage because several parts overlap or hide behind brackets. In addition, repair documentation can help you understand what needs to come off first and what should remain in place until later.

When a repair video is connected to a part reference, the process becomes easier to follow. A diagram shows the part name and number, while a video shows the actual movement required to remove or install it. For example, spring-loaded parts often cannot be explained well with a diagram alone. Seeing how a lever moves, how a gear returns, or how a bracket releases can prevent mistakes.

Therefore, review your available references before touching the printer. This small preparation step can save time and reduce the chance of breaking tabs, stretching springs, or misrouting cables.

Removing the CR Encoder Strip and CR Motor

The first major step is to remove the CR encoder strip. The CR encoder strip is a clear strip that runs across the carriage path. It contains fine markings that allow the printer to track carriage position. Since the strip is delicate, remove it carefully and keep it clean.

If the CR encoder strip remains installed while you remove the carriage, it can get stretched, bent, scratched, or pulled out of position. Therefore, remove it before working deeper in the carriage area. After removal, place it somewhere safe and avoid touching the marked surface.

Next, remove the CR motor belt from the motor pulley. Hold down the motor belt and pull it gently to the right to release the belt from the right side. Then repeat the process on the left side. Once both sides are free, remove the belt from the motor area.

After the belt is out of the way, use a Phillips #1 screwdriver to remove the two screws holding the CR motor. Once the screws are removed, push the motor back. This gives you more clearance and reduces tension around the carriage system.

At this stage, avoid forcing anything. If the belt does not release easily, inspect its path and confirm that it is not caught on a bracket or gear. The carriage belt has teeth on the inner side so it can grip the motor pulley. The belt must later return with the toothed side facing the correct direction.

Removing the Plate, Wires, and Power Supply

After moving the CR motor, use a Phillips #2 screwdriver to remove the two screws that secure the plate. Once the screws are out, remove the plate and loosen the wires underneath or around it.

This step creates more working space and allows access to components behind the carriage system. Take care when handling wires and FFC cables. Flat flexible cables can tear or crease if pulled at a sharp angle. In addition, some connectors have locking tabs that must be released before removing the cable.

Next, remove the power supply. The power supply is secured by three screws. Remove the screws, hold the power supply, and slide it toward you. It should come off once the screws and alignment points are clear.

Although this guide focuses on the carriage assembly, removing the power supply gives you better access to the mechanical parts behind it. However, remember that power supply components can hold electrical charge. Always unplug the printer and allow it to sit before working inside. Do not work on the printer while it is connected to power.

As you remove parts, keep each group of screws separate. For example, store CR motor screws, plate screws, and power supply screws in different containers or labeled areas. This makes reassembly much easier.

Understanding the Change Lever and Transmission Slider

One of the most important areas in this repair is the change lever, also referred to as the transmission slider. This lever slides back and forth and changes the position of a white gear. Because of this gear movement, it is commonly called a change lever.

When the lever moves, it changes the gear position and controls a mechanical function inside the printer. A spring holds the lever back and helps it return to its original position. Before removing the transmission slider, observe how the spring attaches. You will need to put it back correctly during reassembly.

To remove the spring, hold it gently and lift it just enough to release it. Do not overstretch it. Springs in printer mechanisms are small, but they control important movement. If a spring stretches or bends, the mechanism may not return properly.

During installation, pay close attention to the two notches where the spring sits. The spring must rest in the correct notches so the lever can return after being moved. If the spring is installed incorrectly, the lever may stick, fail to return, or leave the gear in the wrong position.

This is one of the areas where the video below is especially useful. The sliding movement and spring return are easier to understand when you see the mechanism in action.

Removing the Cam Holder and Related Parts

After the change lever spring is removed, move to the cam holder. The cam holder looks like a small white box. It is secured by a screw in the front, so remove that screw first.

The cam holder also has a tab on the far side. Loosen that tab carefully. However, do not expect the cam holder to come out immediately. Some black parts toward the back still hold the assembly in place.

To free the area, remove the screws holding those back components. Once the screws are removed, the assembly can loosen, and the cam holder can be removed gently.

The cam holder contains several small parts that must return in the correct order. These include the cam holder body, selection slider, rod, and spring. During reassembly, install the spring first. Then insert the rod. After that, install the selection slider.

This order matters because the spring and rod create the movement needed for the selector to function. If the rod sits outside the correct channel, the mechanism will not work correctly. Likewise, if the spring is missing or installed incorrectly, the selector may not return or engage properly.

Before removing the cam holder completely, take a close-up photo. Then compare your reassembly to the photo before installing the screws.

Removing the Capping Station and Transmission Slider

To remove the transmission slider completely, you need to remove the capping station. The capping station sits near the printhead parking area and helps seal the printhead when the printer is idle. It also supports cleaning and maintenance functions.

The capping station is secured by three screws. Remove the first screw, then the second, and finally the third. Once the screws are out, rock the capping station slightly and turn it toward the back. This creates enough room to move the transmission slider.

After the capping station is moved, push the transmission slider toward the back. Once it clears the surrounding parts, it can come off completely.

At this point, you will also see a large change gear and a large spring for the change gear. Remove the metal bracket if it blocks access. Also, disconnect any FFC cables that prevent the carriage from coming out.

If this is the first time you remove the ET-8550 carriage, you may feel resistance from a hidden part. Instead of pulling harder, stop and inspect the area. A belt, cable, bracket, tab, or wire may still be holding the carriage. Find what is stopping the movement and remove or release it properly.

Removing the Printer Carriage

After the surrounding parts are removed, you should be able to take out the printer carriage. Move slowly and watch the cable path. The carriage connects to multiple electrical and mechanical components, so one missed cable can stop removal.

Once the carriage is out, inspect it carefully. The CR PW cable runs to the carriage sub-board. This sub-board is mounted with the CR encoder reader. The paper width sensor cable runs down to the PW sensor. The APG mechanism adjusts the printhead height.

The APG system is especially important because it controls the height of the printhead over the platen. If the APG mechanism malfunctions, the printhead may sit too high or too low. If it sits too low, the printhead may rub paper or strike raised media. If it sits too high, print quality may suffer because ink droplets have too much distance to travel.

To check APG movement, slide the lever slowly. As the lever moves, a wider part should come out. This part pushes against the frame and raises the printhead. If the movement feels stuck, loose, or uneven, the APG mechanism may need cleaning, adjustment, or replacement.

Understanding the Carriage Belt Orientation

The carriage driving belt has a smooth side and a rough side with teeth. The teeth matter because they engage the motor pulley and help drive the carriage accurately.

When installing the belt, think about the belt as a loop. The inner part of the loop should have teeth so it can hold onto the motor pulley. Only the section that sits inside the carriage has teeth on both sides. This allows the carriage to grip the belt while the motor drives movement.

Incorrect belt orientation can cause slipping, poor carriage movement, grinding noise, or position errors. Therefore, inspect the belt before reinstalling it. If the belt has ink, debris, missing teeth, cracks, or stretching, replace it.

During reassembly, make sure the belt sits cleanly in the carriage and around the motor. It should not twist. It should also have proper tension. Too much tension can stress the motor, while too little tension can cause slipping or uneven movement.

Reinstalling the Transmission Gear and Lever

The transmission lever area requires the most attention during reassembly. Start with the shaft and place the spring on it. Then inspect the gear. The gear has two sides. One side has a recessed area where the spring can sit. The other side is flat.

Install the gear with the flat side facing outward and the recessed side facing toward the spring. Slide the gear onto the shaft and push it into place. Then position the transmission lever so it can push and slide correctly.

With one hand, hold the spring and change gear in position. With the other hand, pull the transmission lever into place. After installation, test the movement. The lever should slide smoothly and return when released.

If the lever does not return, the spring may not be seated correctly. If the gear does not engage, the gear may face the wrong direction or may not sit fully on the shaft. Remove and correct the alignment before continuing.

Do not wait until the printer is fully assembled to test this mechanism. It is much easier to fix the spring and gear now than after reinstalling brackets, the capping station, the motor, and the power supply.

Reinstalling the Cam Gearbox

For the cam gearbox, confirm that the spring sits inside the cam holder. Then install the rod and the switch gear. The transmission box must hold the rod on the transmission lever. In other words, make sure the plastic rod sits inside the box, not outside or beside it.

After installing the screw, test the lever by hand. When you slide the lever toward the right, it should move the gear. When you release it, it should come back. This return motion confirms that the spring and rod are installed correctly.

If the lever sticks, do not force it. Remove the part and inspect the rod, spring, and slider position. A small misalignment can prevent proper movement.

Once the cam gearbox and transmission lever move correctly, you can continue reassembling the remaining printer components.

Final Reassembly and Testing Tips

After the carriage and transmission parts are back in place, reinstall the capping station, metal bracket, power supply, plate, CR motor, belt, FFC cables, and CR encoder strip. Work in reverse order and check each step before moving to the next.

Make sure all FFC cables seat fully in their connectors. A partially seated cable can cause sensor errors, motor problems, or communication failures. Also, route wires in their original channels so they do not interfere with carriage movement.

After reinstalling the CR encoder strip, confirm that it passes through the CR encoder reader. This step is critical. If the strip does not pass through the reader, the printer cannot track carriage position. As a result, the carriage may slam to one side or trigger an error.

Before powering the printer, move the carriage gently by hand if the design allows it. It should move smoothly without binding. Check the belt path, encoder strip path, cable routing, and lever movement.

Finally, power the printer on and observe the startup sequence. Listen for abnormal grinding, clicking, or repeated impacts. If something sounds wrong, turn the printer off and inspect the assembly again.

Repairing the Epson ET-8550 carriage system takes patience, but the process becomes more manageable when you understand each part's purpose. The CR motor drives the carriage, the encoder strip tracks its location, the APG adjusts printhead height, and the transmission slider controls gear movement. With careful disassembly, correct spring placement, and proper belt orientation, you can remove and reinstall the carriage assembly successfully.

BCH Technologies provides parts, repair resources, and video support for printer repair projects like this one. Use the video below along with this guide to compare part positions, confirm gear movement, and avoid common reassembly mistakes.