Epson WF-7520 / PX-1700F Head Slams Left After CR Encoder Replacement: Causes, Error Behavior, and Fix Checks

Question

I have an Epson WF-7520 (Japanese version PX-1700F). After replacing the CR encoder and reassembling the printer, the printhead/carriage moves very fast and crashes into the left side of the printer. Then the printer shows an error and shuts off. Why would it do this after a CR encoder replacement, and how can I fix it?

Answer

What you're describing-carriage moving at high speed and crashing left immediately after a CR encoder replacement-almost always points to one thing:

The printer can't correctly "read" the carriage position.
When Epson printers don't get reliable position feedback from the CR (carriage) encoder system, the control board can't accurately slow/stop the carriage at the correct location. The result can look like a "runaway carriage" that slams into the side and then triggers a fatal error/power-off as a safety response.

Below are the most common causes and what to check.

1) The CR encoder strip is not installed correctly (or is flipped/misaligned)

On many Epson wide-format models, the CR encoder is a transparent plastic strip with fine markings that the encoder sensor reads.

If the strip is:

• not centered in the sensor slot,

• not properly tensioned,

• twisted,

• seated in the wrong track/clips, or

• installed backwards (model-dependent),

...the sensor may read garbage or nothing at all. When that happens, the printer "loses its map" of where the head is.

What to check (power off/unplug first):

• The strip should pass cleanly through the CR encoder sensor window on the carriage.

• The strip must be straight, not bowed, twisted, or rubbing.

• Both ends should be secure in their anchors and have proper tension (not slack).

• Verify the strip is routed exactly as it was originally (a common reassembly mistake is clipping it in front of/behind a guide incorrectly).

2) The CR encoder sensor isn't seated, connected, or aligned

Since you mentioned replacing the CR encoder, you may have replaced the sensor (the reader) rather than only the strip-or you may have disturbed the sensor during reassembly.

If the sensor is:

• not fully seated on the carriage,

• slightly tilted,

• cracked, or

• plugged in loosely (FFC cable not fully inserted/latched),

...the printer may fail to read the strip and the carriage can overshoot.

What to check:

• Make sure the CR encoder sensor is mounted firmly and sits square/parallel to the strip.

• Check the FFC cable for the sensor: it must be fully inserted and the latch must be closed.

• Confirm the cable is not reversed. Many Epson FFCs can be inserted the wrong orientation if you're not careful (contacts facing the wrong way).

3) The encoder strip is dirty, greasy, scratched, or has fingerprints

Even a correctly installed strip can fail if it is contaminated. Encoder systems can be very sensitive.

Common contamination sources:

• fingerprints from handling,

• grease/oil from the mechanism,

• ink mist overspray,

• cleaning fluid residue.

What to do:

• Inspect the strip under bright light.

• If it looks hazy or streaky, gently clean it with a lint-free cloth slightly dampened with isopropyl alcohol (avoid soaking it, and don't use abrasive materials).

• Let it dry fully before powering on.

4) Timing belt or pulley issues after reassembly

Sometimes the encoder replacement coincides with removing parts around the belt system. If the timing belt is not seated properly, too loose, or misrouted, the carriage can move unpredictably and slam.

What to check:

• Belt should be properly engaged with the motor pulley and carriage teeth.

• No belt twist.

• Tension is correct (not floppy, not guitar-string tight).

• Carriage should slide smoothly by hand (with power off) without binding.

5) Carriage home position / left-side sensor issues (less common but possible)

Printers typically "home" the carriage to one side and use a sensor (or mechanical flag) to confirm it reached the home position.

If the printer can't detect home-because:

• the home sensor is blocked or unplugged,

• the carriage flag is missing/misaligned, or

• something is physically blocking the parking station area,

...it may continue driving the carriage until it hits the side.

What to check:

• Ensure nothing is obstructing the left parking area.

• Verify any small plastic flags/actuators moved during disassembly are still present and aligned.

• Confirm related connectors weren't left unplugged.

6) About the "error and turn off" behavior

You mentioned the printer "say error and turn off," but didn't provide a specific numeric error code.

On many Epson models, a serious CR/positioning fault can trigger a protection state that looks like:

• sudden shutdown,

• blinking power/error lights, or

• a carriage jam/position error message.

If you see an on-screen code or a blink-pattern code, that would help pinpoint whether it's explicitly a CR encoder read error, carriage jam, or home position detection fault-but based on your symptoms immediately after encoder work, the encoder strip/sensor alignment or connection is still the top suspect.

Important safety note

Because the carriage is slamming into the frame, I recommend not repeatedly power-cycling and testing until you've proven the encoder strip is correctly routed and readable. Repeated impacts can damage:

• the carriage frame,

• the belt teeth,

• the sensor mount,

• and even the printhead cables.

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems. So, we're not able to provide remote troubleshooting, step-by-step repair guidance, or hands-on support for printer repairs. We do offer an in-person evaluation and repair service through our local diagnostic facility (printer repair service [https://bchtechnologies.com/printer-repair-service]). Because demand is high, we operate on a first-come, first-served basis, and it can take a few weeks before we're able to accept a drop-off. Our services are structured to repair either the entire printer or specific parts, with clear instructions on how to proceed. We also realize our pricing may not be the most economical option, so we strongly encourage self-help through online research first. You can start by checking YouTube or visiting our channel homepage (BCH Technologies on YouTube [https://youtube.com/@bchtechnologies]). To find the most relevant video fast, use the search icon next to "About" on the right side of the menu bar. I receive dozens of questions every day asking for a specific video, and after creating videos over the past nine years, it's hard to remember every topic-so YouTube search is the most efficient. YouTube may also recommend helpful videos from other channels that match your exact symptom.

Thank you again for reaching out and for supporting BCH Technologies. We truly appreciate your viewership and engagement, and I hope this points you in the right direction.