Epson ET-8550 Error Code 100077: Scanner Motor, Encoder, FFC Cable, and Gear Troubleshooting

Question

I recently received an Epson ET-8550, but every time I try to set it up, I get error code 100077. When the printer starts up, the scanner begins moving, but it appears that the scanner motor cannot pull the scanner carriage completely across the scanning surface.

I inspected the cables connected to the scanner and do not see any obvious damage, so I am unsure what to check next. What causes error 100077, and should I be looking at the scanner cable, motor, gears, or another component?

Answer

What Does Epson Error Code 100077 Mean?

Error code 100077 is an "FB BS+ Excess Load Error." In practical terms, the printer commanded the scanner motor to move the scanner carriage, but the scanner motor stopped during the movement or the printer could no longer confirm that the scanner mechanism was moving correctly. (Print Copy)

From your description, this fits the symptoms very well: the scanner begins its startup movement, but the motor is unable to pull the scanner carriage all the way across the scanner bed.

That is important because it suggests that the scanner is not completely dead. The printer is at least attempting to operate the scanner motor. The problem is occurring after the movement begins.

Several different failures can produce 100077, so I would not replace the main board immediately.

1. Check Whether the Scanner Carriage Is Mechanically Binding

The first possibility is excessive mechanical resistance.

The scanner carriage-the part containing the CIS scanner sensor-must travel smoothly along its guide. If it starts moving but encounters too much resistance, the motor may stall and the printer will interpret this as excessive load.

With the printer powered off and unplugged, inspect the scanner mechanism for anything that could interfere with movement. Look for:

• A foreign object inside the scanner mechanism

• A cable that has shifted into the carriage's travel path

• A damaged or displaced carriage guide

• A scanner component that has become mechanically disengaged

• Shipping material or another obstruction that was not removed

• A scanner carriage that is sitting incorrectly on its guide

Do not force the scanner carriage. If it does not move normally, forcing it can damage the belt, gears, carriage, or scanner sensor assembly.

2. Inspect the Scanner Drive Gears and Motor Pulley

Another important possibility is the scanner drive mechanism.

The scanner motor does not move the scanner sensor directly. Its movement is transferred through the scanner's drive components. If a scanner motor pulley becomes disengaged or one of the scanner drive gears cracks, strips, slips, or becomes disconnected, the motor may start but fail to move the scanner carriage correctly. These mechanical failures are among the listed causes associated with error 100077. (Print Copy)

Pay attention to what you hear during startup.

If you hear the motor spinning but the scanner carriage barely moves-or if you hear clicking, skipping, grinding, or repeated attempts to move-that would make me more suspicious of the gears, pulley, or drive mechanism.

A cracked gear can sometimes look perfectly normal until load is placed on it. The crack may allow the gear to slip on its shaft only when the scanner motor attempts to move the carriage.

3. Check the Scanner Encoder and Scanner Scale

The scanner also needs position and movement feedback.

The printer doesn't simply apply power to the scanner motor and assume that the carriage is moving. It needs feedback that tells the control system whether the scanner mechanism is actually traveling as expected.

If the printer fails to read the scanner encoder, it can behave as though the scanner has stopped even if the motor is attempting to move.

Contamination or damage involving the scanner's encoder/scale system is therefore another possible cause of 100077. (Print Copy)

Inspect the scanner encoder components for contamination such as:

• Dust

• Ink mist

• Grease

• Fingerprints

• Adhesive residue

• Scratches or physical damage

If cleaning is required, be extremely gentle. Encoder components are precision parts, and aggressive cleaning can create a problem that was not there originally.

4. Inspect the Scanner FFC Cables Even If They Look Good

You mentioned that you already inspected the scanner cables and they do not appear damaged. That is definitely a good first step, but unfortunately, a visual inspection cannot completely eliminate the FFC cables as a possibility.

An FFC, or Flat Flexible Cable, may appear normal while still having:

• A hairline break in a conductive trace

• Damage at the end contacts

• A crease that broke an internal conductor

• An intermittent connection

• A cable inserted at a slight angle

• A cable that is not fully seated in the connector

• Contaminated electrical contacts

• Damage caused by repeated flexing

For the ET-8550 scanner assembly, the scanner-related FFC connections include functions associated with the scanner motor and scanner data. BCH's ET-8550 scanner cable set, for example, includes the scanner motor, scanner data, and control-panel-related FFCs. (BCH Technologies)

With the printer unplugged, carefully check both ends of the scanner FFCs. Make sure they are inserted completely straight and evenly into their connectors. Also inspect the exposed conductive contacts closely.

Do not repeatedly insert and remove an FFC unnecessarily. The locking connectors and conductive ends can be damaged fairly easily.

5. Use Our ET-8550 Scanner FFC Product Page as a Diagnostic Reference

I recommend looking at our Epson ET-8550 Scanner 3-Cable Combo product page [https://bchtechnologies.com/products/ffc-cable-for-epson-ecotank-et-8550-scanner-3-cable-combo-et8550].

I am not suggesting that you immediately purchase the cables.

The reason I am pointing you to that page is that the product information and associated video can help you understand the ET-8550 scanner cable arrangement and identify the scanner-related connections before you start replacing parts. The scanner cable set includes the scanner motor cable and scanner data cable, which can help you identify what you are inspecting. (BCH Technologies)

Use the information as a troubleshooting reference first. Once you understand which cable controls which function, you can make a much better decision about whether a cable actually needs replacement.

6. The Scanner Motor Itself May Be Failing

Another possibility is a partially failed scanner motor.

This does not necessarily mean the motor is completely dead.

A motor can still start turning but no longer produce enough torque to move the scanner carriage reliably. That would explain a situation where the scanner begins moving and then stops partway through its travel.

This is one reason error 100077 can be more difficult to diagnose than an error where the motor never moves at all.

If the scanner carriage moves freely, the gears and pulley are intact, the encoder system is clean, and the FFC connections test correctly, then the scanner motor becomes a stronger suspect.

BCH Technologies also has an ET-8550 Scanner Motor [https://bchtechnologies.com/products/et-8550-scanner-motor-drives-scanner-cis-unit-during-scanning] available for reference if you need to identify that component. (BCH Technologies)

Again, I would diagnose before purchasing parts.

7. The Scanner Assembly Could Be the More Practical Replacement

If you discover multiple mechanical problems-for example, damaged gears combined with carriage or encoder damage-it may not make sense to replace individual pieces one at a time.

At that point, replacing the complete scanner unit can sometimes be more practical.

This is also one of the service-level corrective actions associated with scanner error 100077. (Print Copy)

Whether that makes financial sense depends on the printer's condition and the availability and cost of the scanner assembly.

8. The Main Board Is Also a Possibility, but I Would Check It Last

Finally, the main board can cause this error.

The main board controls the scanner motor and processes feedback from the scanner system. If the motor drive circuitry or the circuitry responsible for interpreting scanner feedback is damaged, the printer can generate error 100077 even when the scanner's mechanical components are good.

However, based on your description that the scanner actually starts moving, I would not jump straight to replacing the main board.

I would investigate the system approximately in this order:

1. Check for a physical obstruction or scanner carriage binding.

2. Inspect the scanner gears, pulley, and drive mechanism.

3. Inspect the scanner encoder/scale.

4. Reseat and closely inspect the scanner FFC cables.

5. Determine whether the scanner motor is losing torque or stopping under load.

6. Consider replacing the damaged individual component or complete scanner assembly.

7. Consider the main board only after the scanner-side causes have been reasonably eliminated.

The key clue in your case is that the scanner starts moving but cannot complete its travel. That usually directs the investigation toward the movement system-mechanical resistance, gears, motor, encoder feedback, or the scanner motor FFC-before assuming that the entire main board has failed.

If you take additional photos or videos for your own diagnosis, one particularly useful video would be the scanner's complete startup sequence with the sound clearly audible. The difference between a motor that stops silently, a motor that continues spinning while the carriage stays stationary, and a mechanism that clicks or grinds can help distinguish an electrical problem from a gear or mechanical-load problem.

Addressing printer problems can be complicated because many of these failures require hands-on inspection, measurements, disassembly, and testing. For that reason, we're unable to reliably provide individualized remote troubleshooting, repair support, or a guaranteed diagnosis based solely on messages, photographs, or videos. We do offer an in-person evaluation and repair service through our BCH Technologies Printer Repair Service [https://bchtechnologies.com/printer-repair-service]. Because demand is high, repairs are handled on a first-come, first-served basis, and it may take a few weeks before we have availability for you to drop off your printer. Our services are structured so that we can work on either an entire printer or certain individual components, with instructions provided for how to proceed. We also recognize that our repair rates may not be the most economical option for every situation, so we strongly encourage self-help and online research whenever practical. A good place to begin is YouTube, including the homepage of our BCH Technologies YouTube channel [https://youtube.com/@bchtechnologies]. On our channel page, use the search icon near the "About" section to search for your printer model, error code, or component. I receive dozens of questions every day asking whether we have a video on a particular repair. After creating videos for more than nine years, it is difficult to remember every video we've published, so using YouTube's channel search is usually the fastest approach. YouTube may also recommend relevant repair videos from other channels that can help with your particular problem.

Thank you again for contacting BCH Technologies and for supporting our work. I hope this gives you a clearer path for diagnosing error code 100077 without replacing parts unnecessarily. Taking the diagnosis one component at a time-especially the scanner drive mechanism, encoder system, FFC connections, and scanner motor-will give you the best chance of identifying the actual failure.