Epson L1800 Printhead and Mainboard Failure: Causes and Testing Tips to Avoid Repeated Damage

Question:
I have a Procolored L1800 printer, and both the printhead and motherboard failed for the second time. The original parts lasted about 11 months, but the new printhead and motherboard (which cost around $700) only lasted about six weeks, even with proper maintenance. In your video, did you replace all four transistors on the mainboard, or just the second and fourth ones?

Answer:

To answer your question: when troubleshooting and repairing the Epson L1800 mainboard, it's recommended to test all four transistors associated with the printhead firing circuit-not just the second and fourth ones. These transistors are responsible for controlling the electrical signals that drive the piezo elements inside the printhead. If even one of these transistors is shorted or partially failing, it can cause overvoltage or reverse current that damages the printhead beyond repair.

1. Why the Printhead and Mainboard Keep Failing

Repeated printhead and mainboard failures-especially soon after replacement-usually indicate an underlying electrical imbalance or short circuit rather than a random hardware fault. Common causes include:

• Shorted or Leaking Transistors: The L1800's mainboard typically has four key MOSFETs (transistors) in the printhead firing circuit. Even if only one fails, the resulting imbalance can send unstable current to the head, causing internal coil damage.

• Damaged Printhead Ribbon Cable or Connector: If the printhead cable has even a tiny burn mark or kink, it can create resistance or a short circuit between pins, leading to power surges that damage both the head and board.

• Power Supply Spikes: An unstable or failing power supply board (the smaller board near the power cord input) can feed inconsistent voltage, which over time weakens transistor circuits and burns out the head driver IC.

• Residual Damage from the Previous Failure: If the first board failure wasn't fully diagnosed, some damaged components (like diodes or resistors) could have remained in the circuit. Installing a new printhead on a compromised board can destroy the new printhead almost immediately.

2. Testing and Replacing the Transistors

When repairing or inspecting the L1800 mainboard, here are the key steps:

• Use a multimeter in diode mode to test all four transistors. Measure between the gate, drain, and source pins. Any reading close to 0 Ω or identical both directions indicates a shorted or leaking transistor.

• If one or more transistors are faulty, replace all four at once with identical, high-quality equivalents. This ensures even performance and prevents load imbalance across the firing circuit.

• Always inspect the printhead connector area for any burn marks, residue, or corrosion. Clean gently with isopropyl alcohol and ensure the ribbon cable seats snugly without folds or tension.

• If available, use a bench power supply to test current draw before reconnecting the printhead. A sudden surge suggests the board still has an unresolved short.

3. Additional Tips to Prevent Future Failure

• Always test the mainboard independently before installing a new printhead.

• Replace the power supply unit (PSU) if the board or printhead has failed more than once-it's often the hidden culprit.

• Avoid using third-party printheads or parts that aren't electrically matched to the Epson circuit design, as some Procolored units are modified for DTF operation and run at slightly different voltages.

• If you run DTF ink, make sure the printer's internal electronics are well-ventilated; overheating near the transistor area can shorten component life.

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 or repair support. However, we do offer in-person evaluation and repair services at our BCH Technologies local diagnostic facility (https://bchtechnologies.com/printer-repair-service). Because of high demand, service is on a first-come, first-served basis, and it may take several weeks to schedule your printer drop-off. We repair both complete printers and individual components, with clear instructions on how to proceed. While our service rates may not be the lowest, we encourage those comfortable with DIY repairs to explore self-help resources first. You can begin by searching relevant videos on the BCH Technologies YouTube channel (https://youtube.com/@bchtechnologies). Simply use the search icon next to the "About" section to locate tutorials by model or error type.

Thank you again for reaching out and for your continued trust in BCH Technologies. Your engagement helps us share valuable insights and support the global printer repair community more effectively.