Epson WF-7620 Will Not Power On After CR Belt and Mainboard Cable Reconnection

Question

I watched your video, "STOP Cleaning! Dangerous Nozzle Check on Printer WF-7720, WF-7620, and WF-3620," and found it very helpful. I have an Epson WF-7620 and recently replaced the CR carriage belt. During the repair, I disconnected all the cables from the mainboard.

After reconnecting everything and reassembling the printer, it no longer powers on. I also disconnected and reconnected the printhead ribbon cables, and I later discovered that one of the three printhead FFC ribbon cables had been left unplugged.

Could this have damaged or burned the mainboard? What voltage should I expect from the power supply output connector, and what should I inspect to determine why the printer will not turn on?

Answer

A completely unresponsive Epson WF-7620 after replacing the CR belt and reconnecting the mainboard usually points to one of several possibilities: an incorrectly seated cable, a shorted printhead ribbon cable, a damaged mainboard fuse, a power-supply problem, or an accidental connection error during reassembly.

Could an Unplugged Printhead Ribbon Cable Burn the Mainboard?

Leaving one printhead FFC ribbon cable completely unplugged does not always damage the mainboard by itself. In many cases, the printer may still turn on but display an error because it cannot communicate correctly with the printhead.

The more dangerous situation occurs when a ribbon cable is inserted crooked, reversed, shifted by one or more contacts, or inserted while the printer still has electrical power stored in the system. A misaligned printhead ribbon cable can place voltage on the wrong signal line and create a short circuit.

This type of short can damage one or more of the following components:

• A surface-mounted fuse on the mainboard

• The printhead driver circuit

• A MOSFET or voltage regulator

• The printhead itself

• The printhead FFC cable contacts

• The mainboard connector

• The printer's power supply protection circuit

Therefore, the issue may not be that the ribbon cable was unplugged. It may be related to how the cable was reconnected.

Before doing anything else, unplug the printer from the wall and leave it disconnected for several minutes. Do not repeatedly press the power button or continue reconnecting cables while power is present.

Inspect All Printhead FFC Ribbon Cables

The Epson WF-7620 printhead uses multiple flexible flat cables. Each one must be installed completely straight and at the correct depth.

Remove and inspect the printhead FFC cables carefully. Look for:

• Burned or darkened contact pads

• Bent cable ends

• Torn conductors

• Ink contamination

• Corrosion

• Folded or creased sections

• Contacts that are no longer evenly spaced

• A cable inserted at an angle

• A cable shifted sideways in the connector

• A connector locking tab that is broken or not fully closed

The exposed copper contacts must face the correct direction. Ribbon cables that appear physically similar may not all face the same way, so do not assume their orientation without checking how they were originally installed.

Ink or cleaning solution on a ribbon cable is particularly dangerous. Even a small amount of conductive contamination can short adjacent contacts and damage the mainboard when power is applied.

Disconnect the Printhead to Test for a Short

A useful diagnostic step is to determine whether the printhead circuit is preventing the printer from powering up.

With the printer unplugged, disconnect the printhead FFC cables from the mainboard. Keep the cable ends separated and protected so that they cannot touch the frame or each other. Then reconnect the AC power and briefly test the power button.

The printer will not operate normally without the printhead connected, and it may show an error if it powers on. However, if the control panel suddenly lights up with the printhead disconnected, that strongly suggests a short involving one of the following:

• The printhead

• A printhead ribbon cable

• A contaminated connector

• The printhead carriage wiring

If the printer remains completely dead with the printhead disconnected, the problem may be elsewhere, such as the power supply, power-button cable, mainboard fuse, or another incorrectly connected component.

This test must be performed carefully. Never connect or disconnect any ribbon cable while the printer is plugged in.

Check the Power-Button and Control-Panel Cables

During CR belt replacement, it is easy to disturb the scanner, control-panel, or power-button wiring. A printer may appear completely dead even when the power supply and mainboard are functioning if the power-button signal is not reaching the mainboard.

Inspect the cables associated with:

• The control panel

• The power button

• The scanner unit

• The automatic document feeder

• The front-panel display

• The mainboard's low-voltage connectors

Make sure every connector is seated in the correct socket. Some connectors may fit into nearby sockets even when they do not belong there, so compare the cable routing, connector size, wire colors, and board markings.

Also inspect the small locking tabs on the ribbon-cable connectors. A ribbon cable can look installed while making little or no electrical contact if the locking tab is open or damaged.

Check for a Trapped or Pinched Wire

When reinstalling covers after replacing the CR belt, a wire harness can become trapped between the chassis and the plastic housing. A pinched wire can short to the metal frame or interrupt a required power circuit.

Inspect the repaired area and look for:

• Crushed wire insulation

• Exposed copper

• Harnesses trapped beneath screws

• Cables caught under the mainboard shield

• Ribbon cables folded too sharply

• Wires touching carriage or belt components

• Connectors pulled partially out by cable tension

Pay particular attention to the carriage motor, encoder sensor, scanner, control-panel, and power-supply wiring.

Inspect the Mainboard Fuse

Epson mainboards typically include one or more small surface-mounted fuses. These are often labeled with designations such as F1, F2, or another "F" reference, although the exact markings vary by board revision.

A printhead short or incorrectly inserted FFC cable can open one of these fuses. When that happens, the printer may become completely unresponsive or may power on without supplying voltage to a particular circuit.

With the printer unplugged, use a multimeter in continuity mode to test the fuses. A good fuse should normally show continuity or very low resistance. An open fuse may indicate that a downstream component shorted.

However, do not simply bridge or replace a blown fuse before identifying the cause. The fuse is usually a symptom rather than the original problem. Installing another fuse while the printhead, cable, or driver circuit remains shorted may cause additional board damage.

Inspect the Mainboard for Visible Damage

Examine the mainboard under strong lighting and, ideally, magnification. Look closely around the printhead connectors, power connector, fuses, MOSFETs, and voltage regulators.

Warning signs include:

• A burnt odor

• Darkened areas

• Cracked components

• Melted connector plastic

• Corrosion

• Ink residue

• Cleaning-fluid contamination

• Loose components

• Bent connector pins

• Burned ribbon-cable contacts

If the printhead cable was installed incorrectly and the printer was powered on, the damage may be extremely small and not visible without magnification or electrical testing.

Verify the CR Motor and Encoder Connections

Because the repair involved replacing the CR belt, also inspect the carriage motor and encoder-related connections.

The CR motor connector must be installed correctly. The carriage encoder sensor and encoder strip must also be positioned properly. These components would not normally cause a completely dead printer, but an incorrectly connected motor cable or damaged harness could create a short or prevent startup.

Make sure the clear encoder strip passes through the carriage sensor correctly and has not been contaminated, twisted, or placed outside the sensor slot. This is more likely to cause carriage errors after startup than a total power failure, but it should still be checked after a CR belt repair.

Power-Supply Output Voltage

The Epson WF-7620 power supply contains dangerous mains voltage on its input side. Even after the printer is unplugged, internal capacitors may retain a hazardous electrical charge. Testing the power supply should only be performed by someone who is experienced with live electrical measurements.

The exact output voltage can vary according to the power-supply board revision and operating condition. Epson inkjet printers commonly use a higher DC rail for motors and printhead-related circuits, along with regulated lower-voltage supplies generated elsewhere in the printer. However, it is not safe to assume a specific voltage or probe random connector pins without the correct wiring diagram, board markings, or service documentation.

Before performing a live voltage test:

• Identify the power-supply board model number.

• Inspect the connector labels and printed board markings.

• Confirm which pins are ground, output voltage, and control or standby lines.

• Use the correct service manual or schematic for that board revision.

• Avoid touching the primary side of the power supply.

• Do not allow multimeter probes to slip between adjacent pins.

A slipped probe can short the output and destroy a working power supply or mainboard. Because of this risk, beginning with unplugged continuity and resistance checks is generally safer than immediately measuring live voltage.

Isolate the Power Supply From the Mainboard

If you have the appropriate technical experience and documentation, the next diagnostic step is to determine whether the power supply is dead or being pulled down by the mainboard.

A shorted mainboard can cause the power-supply output to collapse. Therefore, measuring no voltage while the power supply is connected does not automatically prove that the power supply is defective.

The power supply may need a control or enable signal from the mainboard before producing its full output, so disconnecting it and expecting a specific voltage can also lead to an incorrect diagnosis. The testing method depends on the board design.

The safest practical approach is to inspect the connectors and fuses first, verify that the control-panel cable is connected, disconnect suspected shorted loads such as the printhead, and then test whether the printer shows any signs of life.

Check for Standby Symptoms

Observe the printer closely when connecting the AC cord. Even if the display remains dark, look and listen for signs such as:

• A brief click

• A control-panel flash

• A faint sound from the power supply

• Scanner movement

• Carriage movement

• A momentary LED

• A repeating ticking noise

A repeated clicking or ticking sound can indicate that the power supply is entering protection mode because of a short. No sound or activity at all may point toward a disconnected power-button cable, missing AC input, failed power supply, open fuse, or dead mainboard.

Also verify the wall outlet, power cord, and AC input connector before assuming that an internal board has failed.

Recommended Diagnostic Order

For this WF-7620, we recommend checking the printer in the following general order:

First, unplug the printer and inspect every cable that was disconnected during the CR belt replacement. Confirm that each connector is in the proper socket and fully seated.

Next, inspect all three printhead FFC cables for damage, contamination, reversed orientation, and misalignment.

Then disconnect the printhead FFC cables from the mainboard and test whether the control panel shows any sign of power.

After that, inspect the power-button and control-panel connections.

Check the mainboard fuses with the printer unplugged.

Inspect the power supply and mainboard for visible damage, corrosion, or burned components.

Only after completing these safer checks should an experienced technician proceed with live power-supply measurements.

There is a real possibility that the mainboard was damaged if one of the printhead ribbons was inserted incorrectly or shorted. However, a completely dead printer does not automatically mean the entire mainboard is beyond repair. The cause could still be an open fuse, disconnected power-button cable, incorrect connector placement, shorted printhead, or power supply that has entered protection mode.

Addressing printer issues can be complicated because many failures require hands-on inspection and component-level testing. For that reason, we are unable to provide individualized remote troubleshooting, repair instructions, or ongoing technical support for printer repairs.

We do offer in-person evaluation and repair through our local printer diagnostic and repair facility [https://bchtechnologies.com/printer-repair-service]. Due to high demand, service is provided on a first-come, first-served basis, and it may take several weeks before an appointment or drop-off opening becomes available. Our services can cover either an entire printer or certain removable components, with instructions provided for the appropriate service process. We also understand that professional diagnostic and repair rates may not be the most economical choice for every situation.

For this reason, we strongly encourage self-guided research before committing to a repair. You can begin with YouTube or visit the homepage of our BCH Technologies YouTube channel [https://youtube.com/@bchtechnologies]. Use the search icon near the "About" section on the channel menu to look for the exact printer model, component, or symptom.

We receive dozens of requests each day asking whether we have videos covering specific repairs. Because we have published printer-repair content for more than nine years, it is difficult to remember every video by title. Searching directly on YouTube is usually the fastest and most effective method. YouTube may also recommend useful videos from other experienced repair channels.

Thank you again for watching our videos, supporting BCH Technologies, and taking the time to share the details of your WF-7620 repair. We sincerely appreciate your trust and hope these diagnostic points help you identify whether the problem involves a cable connection, printhead short, mainboard fuse, or power-supply circuit.