Epson ET-2720 "No Power" After Replacing MOSFET Transistors: Why They Keep Burning at the Parking Position

Question

I watched your video about repairing an Epson ET-2720 "no power" issue (mainboard/formatter board MOSFET repair). I replaced the two transistors and the printer powered on and worked, but after about a minute-right when the printer reaches the parking position-it suddenly shuts off and won't start again. Both transistors are blown again. Do you know why they keep breaking? I also changed the printhead before starting.

Answer

Why the MOSFETs/transistors work briefly-then blow again at the parking position

When a printer powers on after MOSFET replacement but dies again shortly after (especially at a consistent moment like reaching the parking/capping station), that's usually a sign the MOSFETs are not the root cause-they're the victims of an overload or short that appears when a specific subsystem activates.

The parking position is when several things often happen at once:

• The carriage reaches home and the printer may energize certain loads differently

• The printhead/capping/pump system engages

• Carriage cable flexes to a specific bend/position

• Some printers briefly change drive states for head/CR (carriage) control

So the repeatable symptom-runs for ~1 minute, then dies exactly at parking-strongly suggests one of these common causes:

1) A shorted or incompatible printhead (most common)

Even though you replaced the printhead "before starting," the printhead is still one of the top suspects when MOSFETs keep failing.

Here's why:

• On many Epson models, parts of the printhead circuitry are driven by the mainboard through power switching components (often MOSFETs).

• A shorted head (or the wrong head revision) can pull too much current.

• The MOSFET may survive initial startup but fail when the printer runs a different drive pattern during initialization/homing/parking.

Practical takeaway: If the underlying cause is a bad head, replacing MOSFETs repeatedly will keep ending the same way.

2) A damaged/shorting printhead FFC cable (very common and often overlooked)

The printhead ribbon cable (FFC) can look "fine" but still be electrically unsafe:

• Micro-cracks in the traces

• Pinhole burns from a previous short

• Creases that expose conductive layers

• Edge wear that shorts adjacent lines under pressure

And crucially: the cable flexes differently depending on carriage position. Your description-failure at the parking position-fits a scenario where:

• The cable bends sharply at home/park

• Two traces touch (or a compromised trace contacts shielding/ground)

• Current spikes and the MOSFETs fail again

If there's any suspicion, the safest path is: replace the cable before sacrificing more board components.

3) Incorrect MOSFET/transistor part, orientation, or substitution issues

Even if the printer "works" briefly, MOSFET replacement can fail quickly if:

• The replacement isn't truly equivalent (Rds(on), current rating, switching characteristics, gate charge)

• A counterfeit/low-quality part is used

• One device is installed reversed or with poor solder joints

• Thermal transfer is poor (overheating under load)

Some transistors limp through light load, then fail under real load transitions during startup/parking.

4) A downstream short on the mainboard (driver IC, diode, capacitor, or rail short)

Sometimes the MOSFET fails because something else on that same power rail is shorted:

• A shorted ceramic capacitor near the head power rail

• A damaged driver IC feeding the gate

• A shorted diode or protection component

• Burned/open resistors that cause improper gate drive, making the MOSFET run hot

In that case, new MOSFETs can fail quickly because the circuit is still operating outside spec.

5) Mechanical load or carriage/pump events that trigger an electrical spike

Less common but possible: when the printer hits home/park, another load engages (like pump/cap mechanism). If a motor, solenoid, or related wiring is shorted/binding, it can create a power event that stresses switching components. However, in "MOSFET keeps blowing" cases on these Epsons, printhead/head cable are still the first items to clear.

The key diagnostic question (based on your proposed answer)

The most important step is exactly what you hinted at:

Did you identify the root cause of why the printer burned the MOSFET in the first place-such as a bad printhead or a damaged printhead cable?

Because if that cause wasn't eliminated, the repair will repeat:

1. Replace MOSFET → printer powers briefly

2. Load/position change occurs (parking) → short/overcurrent returns

3. MOSFET blows → printer goes dead again

What I would prioritize (in safe, practical order)

• Treat the printhead and printhead cable as the primary suspects when MOSFETs burn repeatedly.

• Inspect/replace the printhead FFC cable if there is any crease, discoloration, or prior damage.

• Verify the replacement MOSFETs are correct spec and correctly installed (same type/class, correct orientation, good soldering).

• Only after those are cleared, consider the possibility of mainboard rail/component damage beyond the MOSFETs.

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems, and that's why we're not able to provide remote troubleshooting, repair suggestions, or remote support for printer repairs. We do offer an in-person evaluation and repair service at 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 may take a few weeks before we can schedule 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. That said, we understand our rates aren't the most economical, so we strongly encourage self-help through online research first. You can start by checking YouTube or visiting our channel homepage at BCH Technologies on YouTube (https://youtube.com/@bchtechnologies). To quickly locate relevant videos, use the search icon next to "About" on the right-hand side of the menu bar. I receive dozens of requests daily asking for videos on very specific topics, and after creating videos for over nine years, it's difficult to remember every one-so YouTube search is the fastest method. Plus, YouTube may recommend related videos from other channels that could help as well.

Thank you again for reaching out and for supporting BCH Technologies. I truly hope this helps you pinpoint the underlying cause so you can stop sacrificing MOSFETs and get your ET-2720 stable again.