How to Fix a Pro-Colored A3 UV DTF Printer When It Prints Varnish but No Colors (Error and Busy LEDs Flashing)

Question:
I have a Pro-Colored A3 UV DTF printer that worked fine a few years ago, but after being cleaned and stored, it's now acting up. When powered on, the printer shows Error and Busy LED lights flashing at the same time. It used to have a heater error, but after replacing the ribbon cable, the heater now works properly. The varnish head prints fine, but no color inks print - it moves back and forth as if printing, but nothing appears. During cleaning cycles, ink discharges into the waste tank normally. Disconnecting one head doesn't change the flashing lights, and the printer software doesn't show any errors. What could be wrong, and how can I fix it?

Answer:

Understanding the LED Lights and Printer Behavior

When both the Error and Busy LED lights on your Pro-Colored A3 UV DTF printer flash simultaneously, it typically signals a communication failure between the mainboard and the printhead board (headboard). This issue often doesn't appear in the software interface because it occurs at the hardware level - before the printer can even process print data.

In simpler terms, your printer is trying to initialize the printhead but can't successfully complete the handshake. This usually means the printer can't detect one or more of the printheads correctly or isn't able to send firing voltage to them.

Since your varnish head still prints, we can deduce that:

• The motion system (carriage and motor) and logic board are still working properly.

• The ink pump and tubing are fine because you can see ink during head cleaning.

• The issue is electrical or signal-related, not a fluid or mechanical problem.

Why the Varnish Prints but CMYK Does Not

The varnish head printing successfully means that one communication channel (usually on a separate driver circuit) is still functional. UV DTF printers often separate the varnish head from the CMYK head system for safety and stability.

If varnish works but colors don't, the problem likely lies in:

• A damaged or oxidized ribbon cable connecting the color printhead.

• A blown fuse on the headboard or mainboard that cuts voltage to the color channels.

• A faulty CMYK driver chip (printhead IC) that failed after prolonged inactivity.

Step-by-Step Diagnosis and Fix

1. Inspect the Headboard LEDs
   When both Error and Busy lights flash, it usually means the printer tried to start the head but failed to receive feedback.

   • Power off and unplug the printer.

   • Wait a few minutes, then inspect the ribbon cables and connectors on both ends.

   • Look for burn marks, oxidation, or dark discoloration on the flat ribbon (FFC) contacts. Even slight residue can interrupt signal flow.

   • Replace the cable if any damage is visible or if it's been repeatedly reinserted.

2. Check Cable Orientation and Seating

   • Ensure the blue tab of the ribbon cable faces the correct direction for each connector (it's easy to insert them backward).

   • Reinsert the cables slowly and evenly to prevent uneven contact.

3. Test Each Printhead Individually

   • Disconnect one printhead at a time and test printing.

   • Normally, if one head is disconnected, the Error LED behavior changes - but if both Error and Busy lights continue flashing together, the issue is likely with the headboard itself, not the printheads.

4. Check for Blown Fuses on the Headboard or Mainboard

   • Look closely for small fuses labeled "F1", "F2", etc., near the head connectors.

   • These are typically 1A to 3A SMD fuses that protect the printhead power lines.

   • If one is blown, the head won't fire even though the printer moves as if it's printing.

   • Replace the fuse if possible, or test continuity with a multimeter.

5. Perform a Voltage Test (Advanced Users)

   • During a print command, measure voltage across the printhead connectors using a multimeter.

   • A healthy board typically pulses between 5V-42V (depending on head model).

   • If you get no voltage, that means the head driver circuit or fuse is open.

6. Firmware and Software Reset

   • Some UV DTF printers use firmware that automatically disables the printhead driver after detecting a short circuit to prevent further damage.

   • Reinstall or reset the printer firmware if possible, or contact Pro-Colored support to get the correct firmware version for your model.

   • Note: Newer boards have built-in head protection logic, so they might not show visible software errors but still block head voltage output internally.

7. Replace the Headboard or Mainboard (Last Resort)

   • If all else fails, the most reliable step is to swap the headboard or mainboard with a known working unit.

   • This can confirm whether the issue lies in the control circuitry or printhead itself.

Common LED Error Patterns and Their Meanings

Even though your software doesn't display any messages, the LEDs can provide diagnostic clues:

• Error + Busy Flashing Together: Printhead communication or voltage failure.

• Error Solid + Busy Flashing: EEPROM or firmware corruption.

• Error Flashing Only: Ink detection or pressure fault.

Given that your Error and Busy lights flash simultaneously, the most probable cause is a printhead communication or voltage delivery issue - either a faulty headboard, a shorted printhead, or a broken ribbon cable.

Addressing printer issues can be a complicated affair due to the hands-on nature of these problems. Therefore, we're unable to offer remote troubleshooting or repair support. However, we do provide in-person diagnostic and repair services through our local diagnostic facility (https://bchtechnologies.com/printer-repair-service). Due to high demand, repairs are handled on a first-come, first-served basis, and it may take a few weeks before we can receive your printer. Our facility services both full-printer repairs and specific part replacements, with clear instructions on how to proceed.

If you prefer to troubleshoot yourself, we highly recommend exploring our BCH Technologies YouTube channel (https://youtube.com/@bchtechnologies). Use the search icon next to "About" on the right-hand side of the menu bar to look for topics like "UV DTF printhead not firing," "ribbon cable repair," or "printer head communication error." After nearly a decade of publishing videos, this is the most efficient way to locate relevant tutorials-and you might even discover other channels offering additional guidance.

Thank you again for reaching out and for your continued support of BCH Technologies. We truly appreciate your patience and the opportunity to help guide you through this complex repair process.