Why Do MOSFETs Keep Burning on My Epson L1800 or 1390 Printer? Diagnosing Power Failures and Printhead Problems

Question:
Why do the MOSFET drivers on my Epson L1800 (or L1390) printer keep burning out, even after I've replaced them multiple times? I measured only 2.56V instead of 42V on the standby line, and I'm also dealing with a clogged red channel in the manifold. Could these issues be related? I'm replacing the manifold and ordered another printhead to test, but I want to understand if a clogged manifold can cause MOSFET failures.

Answer:

Understanding Epson's "Cold Print" Behavior

First off, the voltage reading of 2.56V instead of 42V is normal if the printer is idle. Epson uses a "cold print" standby mode on many of its models, such as the L1800 and 1390, where the printhead receives a low voltage (around 2.4–2.6V) when the printer isn't actively printing. So, this low voltage alone isn’t a sign of a failed MOSFET, but combined with your other symptoms, it helps complete the picture.

Why Your MOSFETs Keep Burning Out

If you're experiencing repeated MOSFET driver failures, it's typically an indication of a more significant electrical issue. Below are the most likely culprits:

1. Short Circuit Downstream

If there’s a clog or mechanical obstruction inside the printhead manifold, it might cause abnormal current draw. More critically, a shortened printhead, especially if ink has leaked onto the FFC terminals or pins, could be overloading the MOSFET circuits. Once you swap in a new driver without isolating the root cause, it simply fries again.

2. Back-EMF Spikes

Solenoids and motors in your printer release voltage spikes (known as back-EMF) when switching states. If the circuit doesn’t include proper flyback diodes or snubber protection, these spikes can damage the MOSFETs over time. This is especially relevant during carriage resets or head cleaning routines.

3. Improper Heat Dissipation

Some clone or aftermarket boards skimp on cooling. If your replacement MOSFETs weren’t upgraded with a proper heatsink or thermal paste, they might be overheating even under typical loads. This is a silent killer for power transistors.

4. Unstable Gate Drive Signals

An unstable or mismatched signal from the printer’s logic controller can cause gate oscillation, where the MOSFET partially turns on and off rapidly, producing excessive heat and potentially leading to self-destruction.

5. Power Surge or Firmware Glitch

Rarely, a corrupted firmware routine or sudden power surge can initiate unexpected switching behavior in the drivers, which might burn out even a properly installed MOSFET.

What You Can Do to Diagnose and Fix

➤ Isolate the Load

Disconnect the printhead, motors, and all external components. Power on the board with just the MOSFET circuit and see if it still heats up. If it does, the board itself may be damaged.

➤ Check Cables and Connectors

Look closely at your FFC (Flat Flexible Cable) lines. If any line is damaged, pinched, or oxidized, it may short internally, causing repeated driver failures. Even arcing between slightly conductive ink residues can burn components downstream.

➤ Use a Clamp Meter

Measure the current draw on the printhead and motors. If a sudden spike happens only when a specific part is connected, you’ve found your problem source.

➤ Upgrade Your MOSFETs

Select a higher-rated MOSFET (with higher voltage and amp ratings), ideally featuring built-in gate protection. Add gate resistors or zener diodes to stabilize the switching.

➤ Use an Oscilloscope

If available, check gate signals and drain voltage for noise or spikes. You'll often find abnormalities right before a MOSFET fails.

BCH Pro Tip: Trace and Isolate

In our lab at BCH Technologies, we sometimes cut traces or lift pins on the PCB to test isolated power rails. You can remove the MOSFET entirely, then apply a known voltage/current using a bench power supply directly to the printhead or motor line. This lets you confirm whether the load is shorted before risking another board.

If you want to go deeper, we also encourage using ultrasonic cleaning only when the head is entirely removed from the electrical connection. Applying ultrasonic energy while a short is present can compound failures.

The Complex Nature of Printer Repairs

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems. Therefore, we're unable to provide remote troubleshooting, suggestions, or support for printer repairs. We offer an in-person evaluation and repair service via our local diagnostic facility (https://bchtechnologies.com/printer-repair-service). Given the high demand, we operate on a first-come, first-served basis. Therefore, it may take a few weeks before we can arrange for your printer to deliver it. Our services are structured to repair either the whole printer or specific parts, with clear instructions on how to proceed. However, we acknowledge that our rates aren't the most economical. Thus, we recommend that you resort to self-help via online research. You can start by checking out YouTube or visiting our YouTube channel's homepage (https://youtube.com/@bchtechnologies). Look for specific videos using the search icon next to "About" on the right-hand side of the menu bar. I receive dozens of queries every day asking about videos for specific topics. Having created videos over the past nine years, it's challenging to remember every single one. Therefore, using YouTube's search function would be the most efficient approach. Additionally, YouTube may suggest relevant videos from other channels that can assist you.

Thanks again for contacting us! We genuinely appreciate your engagement and your dedication to resolving your printer issues. Your curiosity and effort help keep the community thriving, and we’re here to support you in any way we can.