Epson Printer No Power: Are 41-42V Readings Normal or Is the Power Supply Bad?

Question: I'm testing an Epson printer power supply. I see about 41-42 volts on the left side (blue wire), but nothing on the right side. Is that good or bad? I even bought another power supply and got the same readings.

I'm following a no-power test method and measured 41-42V on the left and right side test points. My original power supply shows about 41V on the blue wire, but 0V on the other side. I purchased a replacement power supply from eBay and I'm getting the same readings. Does this mean both power supplies are bad, or is this normal?

Answer: 

Are 41-42V readings "good" on an Epson power supply?

In most Epson inkjet designs, seeing roughly 41-42V DC on the blue wire / primary high-voltage output is a good sign. It strongly indicates the power supply is alive and producing its main rail.

Many Epson printers use a control scheme where:

• The power supply provides a standby/high-voltage rail (often ~41V) to the printer,

• But the mainboard decides when to "enable" or "wake up" the rest of the power outputs, depending on conditions (safety checks, load checks, logic readiness, etc.).

So your situation:

• 41V present on the blue wire → the PSU is generating the expected high-voltage rail ✅

• 0V on the "right side" / other output area → can be normal if the mainboard is not enabling that section ✅

• Same readings on two different power supplies → very strong evidence the power supply is not the root problem ✅✅

If two independent PSUs behave identically, it's extremely unlikely they are both failing the same way-especially if the standby/high-voltage rail is stable.

Why would the "other side" show 0V even when the power supply is good?

This is where Epson's control logic matters. A "no power" symptom is often not caused by the PSU failing to create voltage, but by the system refusing to turn fully on.

Common reasons include:

1) The mainboard is not sending the enable (ON) signal

The PSU can sit there outputting its standby/high-voltage rail, waiting for a logic "enable" from the mainboard.
If that enable never comes, you can measure standby voltage (like your 41-42V) but still see 0V on switched rails.

2) A short or overload on the mainboard (or downstream) triggers protection

Even if the enable signal is present, many supplies will shut down or refuse to start if they detect:

• Overcurrent

• Short circuit

• Abnormal load

A shorted component on the mainboard (or on a connected assembly) can keep the power supply in a "trying but protecting" state. Sometimes this produces a quick flicker of voltage that is too fast to see on a basic meter.

3) Cable/connector damage between the PSU and mainboard

If the PSU produces 41V but the harness has a broken conductor, burnt pin, or loose connector, the mainboard may not receive power correctly or may not be able to signal the PSU.

What to check (visually, safely, no guesswork):

• Look for browned plastic, heat marks, or a "toasted" smell at the PSU connector.

• Inspect pins for corrosion or pushed-back terminals.

• Confirm the connector is fully seated and not cracked.

4) A "power button / control panel / logic" path issue

On some models, the control panel, button board, or a ribbon connection helps signal the mainboard to wake. A damaged ribbon cable or control panel fault can mimic a dead printer even when rails are present.

What your readings most likely mean (bottom line)

Based on what you reported:

• ✔️ Your 41-42V reading is correct/normal and indicates the PSU is functioning at least at the standby/high-voltage stage.

• ❌ Replacing the power supply is unlikely to fix this, especially since a second unit behaves the same.

• 👉 The failure is much more likely mainboard-related (enable signal missing, protection state, shorted component), or a harness/connector issue between the PSU and mainboard.

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems. Because of that, we're not able to provide remote troubleshooting, suggestions, or support for printer repairs. We do offer an in-person evaluation and repair service via our local diagnostic facility, Printer Repair Service (https://bchtechnologies.com/printer-repair-service). Due to high demand, everything is handled first-come, first-served, and it can take a few weeks before we're able to accept a drop-off. Our services are structured to repair either the entire printer or specific parts, with clear instructions on how to proceed. We also understand our rates aren't the most economical, so we strongly recommend self-help through online research. You can begin on YouTube or by visiting BCH Technologies on YouTube (https://youtube.com/@bchtechnologies). To find the most relevant videos fast, use the search icon next to "About" on the right side of the menu bar. I get dozens of messages every day asking if we have a video for a very specific issue, and after making videos for the past nine years, it's hard to remember every single one-so YouTube's search tool is the quickest approach. It can also suggest helpful videos from other channels that match your exact situation.

Thanks again for reaching out and for supporting our work. I hope this clears up what your 41-42V readings mean and saves you from replacing power supplies that are already doing their job.