C604 Capacitor Failure on Epson L1800 CB53 Mainboard: Causes and How to Fix It

Question:

Do you have any documentation or specifications for the C604 capacitor on the CB53 mainboard of the Epson L1800? Mine appears to have blown, and I’d like to know what might have caused it and how to fix it properly.

Answer:

About the C604 Capacitor on the CB53 Mainboard

Unfortunately, we do not have the exact capacitor specifications for C604 on the CB53 mainboard of the Epson L1800. This component is surface-mounted, and its values are not always published by Epson or third-party suppliers. While it’s tempting to just find a similar-sized capacitor and replace it, the fact that it blew in the first place is the more important issue to investigate.

From our experience, when C604 fails, it is typically a symptom of a deeper electrical fault rather than a standalone failure. One of the most common underlying causes is a problem with the Q601 transistor, which acts as part of the power regulation circuit for the board.

Why Simply Replacing the Capacitor Might Not Work

Capacitors like C604 are passive filtering components. When they blow, it's often because they’re subjected to:

• Over-voltage conditions

• Current surges

• Prolonged power leakage from an upstream component

In this case, the Q601 transistor may be partially shorted or leaking power, which causes an overload that C604 cannot handle. Replacing C604 without addressing Q601 may result in the new capacitor blowing again within seconds of powering on the printer.

Suggested Fix: Check or Replace Q601

Before replacing the capacitor, we strongly recommend testing or proactively replacing the Q601 transistor. We offer this exact replacement part here:
QF601 Transistor for CB53 Mainboard – BCH Technologies
(https://bchtechnologies.com/products/transistor-qf601-for-mainboard-cb53-main-l1800-1390-1430-epson-printers-fix-no-power?_pos=1&_sid=fdf8dc83c&_ss=r)

Replacing Q601 along with C604 gives you the best chance at restoring normal operation and avoiding repeated damage. If the capacitor blew violently, also inspect nearby traces and components for collateral damage—especially small surface-mount resistors and other capacitors.

If you’re unable to find the specs for C604, you might try sourcing an SMD ceramic or tantalum capacitor rated between 16V–25V and ~10μF–100μF, but this is only a best-guess range based on its position in the power circuit. Using a multimeter with capacitance testing can help if the component is intact but unreadable.

Repair and Support Options

Printer board repairs like this often require steady hands, soldering experience, and access to a microscope or magnifier. Due to the hands-on nature of diagnosing and replacing board-level components, we’re unable to provide remote assistance. However, we do offer in-person diagnostics and repairs through our service center:
Printer Repair Service – BCH Technologies
(https://bchtechnologies.com/printer-repair-service)

Our repair queue is handled on a first-come, first-served basis and may take several weeks depending on current demand. We can repair entire printers or just individual boards/components depending on your needs. That said, we know our pricing may not be ideal for every customer, so we always encourage self-research for experienced users.

If you want to dig further, check out our YouTube channel homepage (https://youtube.com/@bchtechnologies) and use the search icon near the "About" tab to find videos related to CB53 board repair, transistor replacement, or L1800 troubleshooting. We’ve uploaded content for over nine years, and while we can’t always recall every single video, YouTube’s search function often surfaces the most relevant tutorials.

Thanks again for reaching out to us with your question. We hope this gives you the insight needed to move forward with your repair, and we wish you success in restoring your L1800 to working condition!