ET-8550 Error 031006 After Replacing Fuses: Correct F1 and F2 Fuse Specs and What to Check Next

Question:
I have an Epson ET-8550 with a shorted F1 fuse. I replaced F1 with a 1A fuse, and the printer worked for a few restarts, but then the F2 fuse failed. I replaced F2 with the same 1A fuse, but it keeps blowing, and now I get error 031006. I already cleaned the printhead and the sensor board, checked the flex cables, and they all look fine. I also measured about 15-20 ohms in the fuse area where the scanner and printer side meet on the board. The capacitors seem okay based on meter checks and thermal testing with a bench power supply. What are the exact specifications for the F1 and F2 fuses?

Answer:

For the Epson ET-8550, F1 and F2 are not the same fuse, so replacing both with a generic 1A fuse can definitely cause ongoing problems. If one or both replacement fuses are incorrectly rated, they may survive briefly during startup and then fail again once the board sees a normal current surge or a downstream short. That is why you may have seen it power up for a few restarts before the next failure.

The correct replacement set can be found here: F1/F2 Fuse Bundle for Epson ET-8550 / ET-8500 (https://bchtechnologies.com/products/f1-f2-fuse-bundle-for-epson-et-8550-et8550-et-8500-fix-errors-031004-031005-031006-no-power-issue?_pos=1&_sid=410f7c89e&_ss=r).

Regarding the error codes, the ET-8550 commonly shows:

• 031004

• 031005

• 031006

These codes are often associated with fuse, power rail, printhead, carriage board, or related mainboard protection issues. In practical terms, when the printer detects an abnormal current condition or a protected circuit is no longer behaving normally, it may throw one of these 03100x errors.

In your case, since F1 was originally shorted, and then F2 started blowing repeatedly, there are a few realistic possibilities:

First, the fuse replacement itself may not be correct. Because F1 and F2 have different specifications, installing the same 1A fuse in both positions is not a safe assumption. Even if the fuse physically fits, the electrical behavior may be wrong. Some board protection circuits are very sensitive to fuse characteristics, including current rating and response behavior.

Second, there may still be a downstream short or overload. A fuse usually fails for a reason. If F2 keeps blowing, that often means the circuit protected by F2 is still drawing too much current. Even though the flex cables look fine visually, damage is not always visible. A printhead cable can appear normal and still be carbon-tracked, partially shorted, or internally damaged. The same goes for the printhead itself, carriage board, sensor board, or a component on the mainboard.

Third, the original event that blew F1 may have damaged another component that is now causing F2 to fail. This is common in printer boards: the fuse is the obvious failed part, but not always the only failed part. If a MOSFET, regulator, driver IC, or a section of the printhead circuit was weakened, the printer may continue blowing fuses even after replacement.

Your measurement of around 15-20 ohms in the fuse area is helpful, but by itself it does not fully confirm whether the circuit is healthy. On low-voltage printer rails, that resistance may or may not be normal depending on exactly where the measurement was taken and whether the load is still connected. Resistance readings in-circuit can also be misleading because you may be measuring through multiple components in parallel. Since your capacitors checked out and you did a thermal check with a bench supply, that suggests you are already approaching this correctly, but it still does not completely rule out a partially shorted head, cable, or board-level semiconductor.

Here is the direction I would suggest:

Start by replacing F1 and F2 with the correct ET-8550-specific fuse pair, not two identical 1A substitutes. That is the first step, because without the correct fuse values, the troubleshooting path gets distorted.

Then, if the problem continues, isolate likely loads as much as possible. In many cases, repeated fuse failure points to one of the following:

• the printhead

• the printhead FFC/flex cables

• the carriage board or sensor board

• a fault on the mainboard power distribution circuit

Since you already cleaned the printhead and sensor board, the next question is not only cleanliness, but whether one of those parts is electrically damaged. Residual moisture, ink contamination, or carbonized residue around the printhead contacts or cable ends can also create leakage paths. Even very slight contamination can matter on these circuits.

Also pay close attention to whether the error appears immediately at power-on or only after initialization begins. If it blows during startup movement or during printhead initialization, that leans more toward a loaded circuit becoming active only after boot. If it blows instantly, that usually suggests a more direct short on the protected rail.

One more caution: every time a wrong fuse is installed and blows again, there is a risk of compounding the board damage. So I would avoid repeated power-up testing with generic substitutes. It is better to stop, install the correct fuse pair, and continue from there with controlled troubleshooting.

Printer electrical faults can be difficult to diagnose remotely because they are very hands-on by nature. For that reason, we are not able to provide remote repair troubleshooting or step-by-step repair support beyond general guidance. We do offer an in-person evaluation and repair option through our local diagnostic facility (https://bchtechnologies.com/printer-repair-service). Because demand is high, everything is handled on a first-come, first-served basis, and it may take a few weeks before we are ready to receive your printer. Our service can be arranged either for a complete printer or for specific parts, and the instructions are clearly outlined on the service page. That said, we understand our repair rates may not be the most budget-friendly, so we strongly encourage self-help research as well. A good place to start is YouTube, including our BCH Technologies YouTube homepage (https://youtube.com/@bchtechnologies). Use the search icon next to "About" on the right side of the menu bar to look for videos on your exact issue. We receive many questions every day about whether a video exists for a certain repair topic, and after creating videos for so many years, the fastest way to locate one is usually YouTube's own search tool. It may also recommend useful videos from other channels.

Thank you again for reaching out and for your support. We truly appreciate your trust in BCH Technologies, and we hope this helps point you in the right direction.