Epson 1390 Print Carriage Slamming: Motherboard, Thermistor, Encoder Strip, and CR Sensor Troubleshooting

Question

I have an Epson 1390, and the print carriage is slamming hard from side to side. Can you help me figure out what may be causing this problem?

When I first purchased the printer, I noticed that the motherboard appeared to be missing a small transistor or component. Later, I purchased another motherboard, but the seller told me it might need to be reprogrammed to work with the printer. I have already replaced many parts, including the print carriage, the small board on the back of the carriage, and the encoder strip. Most of the parts on this printer have been bought brand new and changed. I am wondering if the issue could still be related to the motherboard not being programmed correctly.

Answer

For the Epson 1390, carriage slamming is usually not caused by the motherboard needing to be "programmed." It is much more commonly caused by the carriage position detection system. On this model, the printer needs to know exactly where the carriage is at all times. If the printer loses track of the carriage position, the carriage may shoot to one side and slam into the frame because the logic board is still trying to move it while receiving incorrect or missing position feedback.

The most common causes are the CR encoder sensor, the CR scale, also called the encoder strip, and the way the carriage reads that strip.

The clear plastic strip running behind the carriage is the CR encoder strip or CR scale. It has very fine markings on it. The carriage sensor reads those markings while the carriage moves. If the strip is dirty, scratched, installed backward, twisted, not seated correctly, or running outside the slot of the encoder sensor, the printer may not be able to determine the carriage location. When that happens, carriage slamming is very likely.

Even though you replaced the encoder strip with a new one, I would still check the following carefully:

Make sure the encoder strip passes directly through the slot of the CR encoder sensor on the back of the carriage. It is easy to accidentally place the strip slightly outside the sensor gap during installation. If the sensor cannot "see" the strip, the printer may behave as if the carriage position is unknown.

Also check that the strip is installed in the correct orientation. Some encoder strips have a correct front/back or left/right orientation. If it is reversed or not seated properly in its hooks, the carriage movement can become erratic.

Inspect the new strip for fingerprints, ink mist, grease, scratches, or bent areas. Even a new strip can be contaminated during installation. Clean it gently with a lint-free cloth and a small amount of distilled water or suitable cleaner. Avoid harsh rubbing because the markings on the strip can be damaged.

Next, inspect the CR encoder sensor itself. Since you replaced the print carriage and it came with a new board on the back, that board may include or connect to the CR sensor. However, "new" does not always mean "good," especially if the replacement part is aftermarket, pulled from another machine, or damaged during shipping. Make sure the sensor is not blocked with dust, dried ink, or debris. Also check that the carriage board cable is fully seated and not damaged.

A loose, reversed, contaminated, or damaged FFC cable between the carriage board and main board can also cause position-reading problems. If the printer cannot receive a clean signal from the CR encoder sensor, the carriage may slam even if the sensor and encoder strip are new.

Regarding the missing component you noticed on the motherboard, I think you may be referring to the thermistor on the heat sink, not a transistor. If the thermistor is missing or defective, the printer may complain about the printhead temperature. It may detect that the printhead is too cold or outside the expected temperature range. That type of problem can trigger temperature-related errors, but it usually does not cause the carriage to slam. A thermistor or temperature-sensing issue is more likely to stop the printer, report a printhead temperature error, or prevent normal initialization rather than cause uncontrolled carriage movement.

That said, the motherboard can still be involved if the CR motor driver, encoder signal circuit, carriage cable connector, or related logic circuit is damaged. However, I would not make the motherboard the first suspect unless the encoder strip, CR sensor, carriage board, cable, and mechanical movement have all been verified.

You also mentioned that the replacement motherboard may need to be reprogrammed. On the Epson 1390, this can be a tricky area. There are not many people who truly know how to handle the Epson 1390 EEPROM properly. The EEPROM contains printer-specific information, settings, counters, and calibration data. If the board came from a different printer, there may be differences in stored values. However, a mismatched or uninitialized board would more commonly cause communication, initialization, waste ink counter, region, ink system, or calibration-related issues. It is less likely to be the direct cause of carriage slamming unless the board itself is defective or cannot correctly process the encoder signal.

A good next step is to connect to the printer with the Epson Adjustment Program and check the actual error code. The error code is important because it can tell whether the printer is detecting a CR motor error, carriage movement error, encoder error, PF error, fatal error, or another specific failure. Without the exact error code, the diagnosis is mostly based on symptoms.

For carriage slamming, you may see errors related to the carriage return system, such as a CR motor error, CR encoder error, or general fatal error depending on how the printer reports the failure. If the printer is detecting a printhead temperature issue because of the missing thermistor, that would point in a different direction. Therefore, reading the code from the Adjustment Program is much more useful than guessing.

If your goal is only to update firmware, then the Epson Adjustment Program may help, and there is also software such as WICReset that can perform certain firmware or maintenance-related functions on supported Epson models. However, firmware updating and EEPROM programming are not the same thing. Updating firmware does not necessarily rewrite all printer-specific EEPROM values. If the board truly needs Epson 1390 EEPROM work, that is a more specialized job.

Here is the troubleshooting order I would suggest:

First, check the mechanical movement. With the printer powered off, gently move the carriage by hand. It should move smoothly across the rail without binding. If it catches, grinds, or feels uneven, inspect the carriage rail, belt, pulley, parking station, printhead lock, and any obstructions in the carriage path.

Second, check the CR encoder strip installation. Confirm that it is routed through the sensor slot, seated correctly on both ends, not twisted, and clean.

Third, check the CR encoder sensor and carriage board. Make sure the sensor is clean and that the carriage board is properly connected.

Fourth, inspect all FFC cables. A cable can look fine but still have a cracked trace, damaged end, poor connection, or slight misalignment. Re-seat the cables carefully and check for bent pins or ink contamination inside the connectors.

Fifth, use the Epson Adjustment Program to read the error code. The exact error code will help determine whether the printer is complaining about the CR system, printhead temperature, motherboard communication, or another subsystem.

Sixth, only after confirming the encoder system and carriage wiring, consider the main board as a suspect. If the replacement board was not properly matched, has damaged circuits, or has a corrupted EEPROM, it may create problems. However, for a carriage slam, I would still focus first on the CR encoder sensor, CR scale, carriage board, and cable path.

In your case, since you have already replaced many parts, I would be especially suspicious of installation alignment rather than the parts themselves. The encoder strip may be new, but if it is not passing through the sensor correctly, the symptom can remain exactly the same. The carriage may also have a new board, but if the FFC cable is not seated perfectly or the connector is damaged, the printer still may not receive the encoder signal.

Addressing printer issues can be a complicated affair because many of these problems require hands-on inspection. For that reason, we are not able to provide remote troubleshooting, repair suggestions, or direct support for individual printer repairs. We do offer an in-person evaluation and repair service through our local diagnostic facility: BCH Technologies Printer Repair Service [https://bchtechnologies.com/printer-repair-service]. Because demand is high, we operate on a first-come, first-served basis, so it may take a few weeks before we are able to accept your printer for drop-off. Our services are structured to repair either a complete printer or specific parts, with clear instructions on how to proceed. However, we understand that our rates may not be the most economical option for everyone. Therefore, we strongly recommend self-help through online research whenever possible. A good starting point is YouTube or our own channel homepage: BCH Technologies on YouTube [https://youtube.com/@bchtechnologies]. Once you are on the channel page, use the search icon next to "About" on the right-hand side of the menu bar to search for specific topics. I receive dozens of questions every day asking which video covers a certain issue. Since we have created videos for many years, it is difficult to remember every single one, so YouTube's own search function is often the fastest way to locate the right video. YouTube may also recommend helpful videos from other creators that are relevant to your repair.

Thank you again for reaching out and for supporting BCH Technologies. I hope this helps point you in the right direction. For this particular Epson 1390 carriage-slamming issue, I would start with the CR encoder strip, CR encoder sensor, carriage board connection, and cable seating before assuming the motherboard EEPROM is the main cause.