Epson L1800 F1 Fuse Blower: Problems And Solutions After Power On

Question:

So, I replaced the blown transistors in my Epson L1800 (again), and now the front power button works again. The printer starts up fine. But even then, I disconnected the head cables completely from the mainboard as a test, and the F1 fuse still blew three seconds after I powered the printer. I am not alone in this experience; I have tried this several times, and it continues. What's causing the issue?

Answer:

In this case, I suggest checking the F1 relay.

If a fuse blows multiple times after removing printhead cables, it usually suggests a short circuit at the mainboard rather than a problem with the printhead itself. In the Epson L1800, the F1 fuse protects the power supply circuit. If the F1 fuse burns quickly, the output surges.

Potential Causes and How to Diagnose Them

Mainboard Short Circuit

So, because the printhead is not working, the mainboard has likely malfunctioned.

Inspect the PCB for burnt components, discolored traces, or damaged capacitors. A shorted capacitor or MOSFET in the power circuit is a typical point of failure.

Driver IC Malfunction

These IC chips operate the voltage of the print heads (provide the 5+/—voltages) and can short internally.

Incorrect or faulty driver IC could lead to a sudden rise in power and power drawing, therefore blowing the fuse.

Check for shorts across the pins of the driver chips with a multimeter in continuity mode.

Backtracking through Voltage Checking

To begin, without replacing parts at random, consider the following:

Strike the F1 fuse from the mainboard, and power up.

Next, measure the voltage reading on each side of the fuse pads.

Trace back from the fuse to find the device drawing too much current.

Capacitor or MOSFET Failure

When this happens, the most common suspects are shorted MOSFETs in the power delivery circuit.

The MOSFETs can be cross-checked for resistance via OPM until you reach the base for detection. A MOSFET with a near-zero resistance between the source and drain is undesirable and needs to be replaced.

What You Can Do Next

Before confirming faults on components, check them individually instead of swapping random electronics.

Analyze power rails, as shorts near driver dot may cause the power rails to short.

And if you can't find the problem, replace the mainboard.

Need Further Assistance?

Unfortunately, it is complex working with the printer mainboards, and often necessitates hands-on inspection and specific tools. While we do not offer remote diagnostics, we provide repair services for customers needing printer repair at our BCH Technologies repair facility, available at https://bchtechnologies.com/printer-repair-service, where you will be serviced on a first come basis. We may be waiting at this time due to high demand.

If you are a self-repair enthusiast (we recommend searching for solutions on YouTube). Head to our YouTube channel (https://youtube.com/@bchtechnologies) and search for how to diagnose mainboard shorts and troubleshoot videos.

Once again, thank you for your patience and support. We hope this guide helps you identify the problem. Comment below if you need more help!