Epson R1390 Power Supply Schematic and Troubleshooting Tips for No Power Issues

Customer Question:

I'm currently rebuilding two printers—an Epson L1800 and an older Epson R1390. Right now, I’m having trouble with the R1390’s power supply. There’s no power at all, and I’m planning to replace the NCP1207A chip. However, some components on the board appear to be damaged, and I am unable to identify them. Do you happen to have a schematic diagram for the power supply circuit?

Answer:

Accessing the Power Supply Schematic:

To help you with your R1390 power supply issue, we do have a schematic diagram available that matches the C589 series used in several Epson printers, including the R1390. You can find it here on our website:
Schema for Epson Power Supply (C589/C589PSB/C589PSE)
https://bchtechnologies.com/products/schema-for-epson-power-supply-c589-c589psb-and-c589pse

This schematic should give you a detailed reference for tracing voltage paths, identifying components (even those that are charred or unlabeled), and confirming proper replacements.

About the NCP1207A and Common Issues:

You're absolutely right to consider the NCP1207A as a point of failure—this chip is commonly used in switching power supply circuits in Epson printers. If you're getting no power at all, here are a few common causes to examine:

1. Damaged or Open Startup Resistors:

   • These feed initial voltage into the NCP1207A from the rectified mains. If open or burned out, the chip will never start.

2. Shorted MOSFET or Primary Side Diode:

   • If the power MOSFET controlled by the NCP1207A has failed short, it could have damaged both the IC and other upstream components.

3. Leaking or Bulging Electrolytic Capacitors:

   • Power rails will fail if the caps are dry or degraded—this is often visually apparent.

4. Open Feedback Loop or Bad Opto-isolator:

   • A failed opto can prevent voltage regulation and power startup.

5. PCB Burn Marks or Heat Damage:

   • If you see discoloration or broken traces, repair them carefully and ensure no solder bridges.

Replacing just the NCP1207A without identifying upstream or downstream faults may cause the new IC to fail as well. Always check surrounding components first—especially the startup resistors, switching transistor, diodes, and capacitors.

Component Identification Tips:

When you encounter burnt or unrecognizable components:

• Use the schematic diagram above to determine their function and specs.

• Cross-reference nearby working boards if you have another printer.

• Consider purchasing a donor board from eBay or salvage for visual comparison.

• You can also measure pad voltages if power can be safely applied with current-limited supply.

If you're experienced with component-level repair and have access to basic diagnostic tools (multimeter, ESR tester, bench PSU), this can be a very rewarding DIY project.

Just as a reminder: Repairing printer electronics—especially power supplies—involves delicate hands-on work and some experience in electronics diagnostics. For that reason, we’re not able to provide remote, detailed troubleshooting or repair walkthroughs. However, we do offer an in-person diagnostic and repair service through our local repair facility (https://bchtechnologies.com/printer-repair-service). Please note that due to the high number of repair requests, we operate on a first-come, first-served basis, and wait times for drop-off or evaluation may span a few weeks. We’re happy to work on either a full printer or a single subassembly like the power board, but we also recognize that our pricing may not suit every budget. For those with a DIY spirit, we strongly recommend supplementing your repair with YouTube tutorials. You can find useful videos directly on our YouTube channel homepage (https://youtube.com/@bchtechnologies). To find relevant topics, use the search icon next to the "About" tab. With nearly a decade of content, that’s the fastest way to pinpoint help.

Thanks again for your kind words and for reaching out. We’re thrilled to be a resource in your restoration project, and we wish you the best of success reviving your R1390 and L1800!