How to Test an Epson Printhead Using a Multimeter: Step-by-Step Guide

When your Epson L1800 or 1390 printer starts showing poor print quality or stops printing entirely, one of the key components to check is the printhead. A faulty printhead can cause serious damage to your printer's mainboard if not identified early. In this post, we'll go over how to test an Epson printhead using a multimeter. This process helps determine whether the printhead is still good or if it has developed shorts or open circuits that could harm your equipment.

We've also included a video below that demonstrates the complete testing process in real-time for better clarity and accuracy.

Understanding the Printhead Connections

Epson printers such as the L1800 or 1390 have two main cables connected to the printhead: a narrow cable and a wide cable. The narrow cable contains nine pins, while the wide cable has 27 pins. Knowing which pin is which is crucial for accurate testing.

When preparing for the test, note that some areas on the cable might appear to have pins but are not actually connected. Always count carefully to identify the real first pin on each cable. For beginners, using a real printed cable from BCH Technologies can make this process much easier. These cables are designed to provide clear pin indicators and ensure accurate readings.

Preparing the Testing Setup

Before testing, arrange your cables neatly. The wide cable often splits into two sections-one combined with the narrow cable, and another that stands alone. Label these or keep them organized in a way that you can easily identify them during testing.

Position the silver (metallic) sides of the cables facing you, with the cables pointing upward. This alignment helps you connect the multimeter probes consistently. If you plan to test several printheads, it's smart to create a small testing station or "kit" where cables are fixed in place for repeated use.

Setting the Multimeter Correctly

A reliable multimeter is essential. Turn your multimeter to diode mode-this mode measures both continuity and voltage drop, which helps evaluate the capacitors within the printhead circuit. You'll see a small diode symbol (►|-) on the dial.

In this mode, when the probes touch the right pins, the multimeter shows readings in millivolts (mV). These readings indicate how well the internal circuits and capacitors are functioning. A good printhead will have readings that closely match the reference chart values.

You can find a free sample testing chart on bchtechnologies.com by typing REF-L1800 test in the search bar. The sample chart provides a limited selection of common pin readings, while the paid version includes all pin values and test points for detailed analysis.

Reading and Interpreting Results

When testing, always place the red probe on pin 1 and use the black probe to touch the other pins sequentially. Record each value displayed on your multimeter.

For example, when measuring between pin 1 and pin 2, a healthy reading might be around 875 mV, which matches the sample chart. Minor variations (within 10-20%) are acceptable. These readings represent the capacitors inside the printhead and give you insight into its overall health.

However, pay close attention to any pin that shows OL (Over Limit) or a significantly lower reading than expected. OL indicates an open line, while a very low or zero reading suggests a short circuit. A single shorted pin can burn out your printer's mainboard, so this step is critical.

Pins such as pin 12 on the wide cable often appear as OL in a good printhead. If that pin suddenly shows resistance, it's a red flag that the printhead is defective. Conversely, if all readings align with the reference chart, your printhead is likely safe to use.

Identifying Faulty Printheads

When a printhead shows a non-OL reading where an OL should be, it means there's a short in that part of the circuit. For instance, pin 15 on the wide-together cable (the combined section) often becomes problematic. If it doesn't display OL but instead shows a reading like 500-600 mV, it's a clear indicator that the printhead could damage your mainboard.

Even one faulty pin can make the entire printhead unsafe. To avoid damaging your printer, always double-check all suspect readings before reconnecting the printhead. If you discover a bad unit, mark it and keep it separate from functional ones.

A good printhead, on the other hand, will show consistent readings where required, with proper OL values in the designated pins. Testing all "OL pins" according to the reference chart ensures that your printhead won't short-circuit your printer.

Using Reference Charts for Accuracy

Testing printheads without a guide can be confusing. That's why BCH Technologies provides reference charts that include all pin numbers, their corresponding expected values, and notes on how to interpret each reading.

For example, the L1800 testing chart clearly identifies the correct ranges for each pin pair. It also indicates which pins are inaccessible (like pin 14 on the printhead) and how to compensate when those cannot be measured. By comparing your readings with this chart, you can quickly determine if the printhead is repairable or needs replacement.

If your printhead shows deviations of more than 20% from the standard reading, it's advisable to treat it as faulty. Sometimes, a printhead that appears bad may simply be wet or clogged with dried ink. Allowing it to dry completely before retesting can sometimes restore proper readings.

Next Steps and Ongoing Testing

After testing your Epson L1800 or 1390 printheads, consider expanding your diagnostic toolkit to include models such as XP600, ET-8550, XP-15000, DX5, DX7, and even newer series like the 33200. The testing process remains largely similar-what changes are the pin configurations and expected readings.

BCH Technologies is developing a resource called "Boardwalk", a comprehensive visual walkthrough of mainboards like those in the ET-8550. This tool will help users identify and test individual electronic components on the printer's circuit board-making repair work more accessible and educational.

To practice, continue using the diode mode on your multimeter and the printed cables available at BCH Technologies. With patience and consistency, you'll gain a strong understanding of how printhead circuits behave and how to catch issues before they become costly repairs.

Final Thoughts

Testing your Epson printhead with a multimeter may sound intimidating at first, but once you understand the pin layout and how to interpret readings, it becomes a straightforward diagnostic process. By following structured steps and using reference materials from BCH Technologies, you can confidently determine whether a printhead is safe for use or needs replacement.

This simple test can prevent expensive damage to your mainboard and extend the life of your printer. To see how the process looks in action, make sure to watch the video below for a visual walkthrough.