Epson ET-2720 No Power: Power Supply Voltage and 4-Wire Connector Testing

Question

I'm troubleshooting an Epson ET-2720 that has no power after watching your video about repairing the printer mainboard, formatter board, transistor, and MOSFET. What voltage should I expect from the power supply? The connector has four wires-should three of those four wires show a voltage reading?

Answer

First, be careful not to confuse the ET-2720's AC input specification with the DC voltages produced inside the printer. Epson specifies the ET-2720 for a 100-240 VAC, 50-60 Hz power supply input. That is the voltage entering the printer from the wall; it is not what you should expect on the low-voltage connector between the internal power-supply board and the mainboard.

Regarding the internal power supply, many Epson inkjet designs use a relatively high DC rail-often around 42 VDC-for motors, printhead-related circuitry, and other higher-power sections. However, I would not treat 42 V as a guaranteed specification for every pin on the ET-2720's four-wire connector unless you have the exact circuit diagram or pinout for that power-supply revision. Epson uses different power-supply designs across models and board revisions, and the publicly available ET-2720 documentation does not establish that three of those four wires should all carry the same voltage.

Therefore, no, I would not assume that three out of the four wires should show a voltage reading. A four-wire connection can include power, ground, enable/control, feedback, or other signaling lines. One pin may be ground, another may carry a main DC rail, and the remaining pins may behave differently depending on whether the printer is off, starting, or being commanded by the mainboard.

This is particularly important because Epson power systems can use communication or control between the mainboard and the power-supply section. In other Epson designs, the mainboard supplies a control signal to the power supply, so a higher-voltage output may depend on the printer's operating state rather than simply appearing continuously whenever AC power is connected. Epson service documentation for other printer platforms shows this type of arrangement with a main DC rail and a control signal from the mainboard.

How to Approach the Four-Wire Connector

The first thing you need to establish is ground. Once you positively identify the DC ground pin, measure each of the other pins relative to that ground rather than simply measuring randomly from wire to wire.

You may find one main supply voltage and one or more control or feedback signals. You may also find that a voltage appears only during startup or after the mainboard requests it. Because of this, measuring the disconnected power supply can sometimes produce different results from measuring it while connected to the mainboard.

Once power reaches the ET-2720 mainboard, you should also expect the board itself to contain several different regulated voltages. Logic sections commonly operate at voltages such as 3.3 V and approximately 1.8 V, while other sections operate from higher rails. Therefore, you should definitely not expect the entire mainboard to measure around 42 V. Voltage regulators and DC-to-DC converter circuits reduce the incoming voltage to the levels required by the processor, memory, sensors, communication circuits, and other electronics.

If the ET-2720 Is Completely Dead

For a printer showing absolutely no signs of power, the diagnosis is really about following the power path through the machine. You are trying to determine whether AC power reaches the power-supply board, whether the power supply is producing its expected output, whether any enable or feedback signal between the mainboard and power supply is functioning, and whether the mainboard's lower-voltage rails are being generated.

If the power-supply output is present but the printer remains completely dead, the problem may be on the mainboard rather than the power supply. Possibilities can include a blown fuse, damaged MOSFET or transistor, failed voltage regulator, shorted capacitor, damaged DC-to-DC converter, or another component pulling a power rail down.

If the expected main supply voltage appears briefly and then collapses, that can also be meaningful. A short circuit or excessive load downstream may cause a protected switching power supply to shut itself down. In that situation, replacing the power supply alone may not solve the problem because the actual fault could be on the mainboard or another connected circuit.

Likewise, if you find a normal high-voltage rail but do not find the expected 3.3 V or other logic supply on the mainboard, concentrate on the mainboard's regulator, fuse, MOSFET, and short-circuit protection circuitry rather than assuming the power supply is defective.

Important Safety Warning

Please use extreme caution while testing this area. The primary side of the ET-2720 power supply is connected directly to mains electricity. Epson's service documentation specifically warns that high voltage exists in the power-supply unit and instructs technicians to disconnect the product from its power source before servicing it. Capacitors can also retain dangerous charge after the printer has been unplugged.

If you are measuring the four-wire low-voltage output connector, keep your probes strictly on the isolated secondary side. Do not probe the AC input, bridge rectifier, primary switching transistor, or large primary capacitor unless you are trained and properly equipped to work on live switch-mode power supplies.

Addressing printer problems like this can be difficult because electrical diagnosis is very hands-on, and readings can change depending on the exact board revision and operating condition. For that reason, we're not able to provide individualized remote troubleshooting or guide someone through live electrical repair measurements. We do offer in-person evaluation and repair through our printer diagnostic and repair service [https://bchtechnologies.com/printer-repair-service]. Because demand is high, the service operates on a first-come, first-served basis, and there may be a waiting period before a printer can be dropped off. Our services cover either complete printers or certain individual parts, with instructions explaining how to proceed. We also recognize that professional repair is not always the most economical option, so we strongly encourage self-help research when appropriate. A good place to begin is YouTube, including the BCH Technologies YouTube channel [https://youtube.com/@bchtechnologies]. Use the channel's search icon near the About section and search terms such as "ET-2720 no power," "ET-2720 mainboard," "Epson MOSFET," or "Epson power supply." We have produced repair videos for many years, so searching the channel is usually much more effective than trying to locate a particular video manually, and YouTube may also recommend useful material from other repair channels.

Thank you again for watching our videos, supporting BCH Technologies, and taking the time to ask such a detailed question. I hope this helps clarify why you should not expect three of the four wires to automatically show the same voltage and gives you a better framework for understanding the ET-2720's power system.