i replaced all the inks in my ts6420a but it still says one is empty or missing, what gives?

Diagnosis

The Canon PIXMA TS6420a utilizes a specific chip-based communication system to monitor ink levels and authenticate cartridges. When the printer reports a cartridge is "empty or missing" immediately after a replacement, it is almost always a failure of the electrical handshake between the gold contact pins on the printhead and the copper pads on the cartridge chip. This is typically caused by a microscopic layer of oxidation on the contacts, a misalignment of the cartridge seat, or a "ghost" error where the printer's internal memory is still holding the status of the previous depleted tank. To confirm the specific cause, look at the OLED screen on the printer. If it displays "Cannot recognize ink cartridge (Error: 1600)" or "The ink has run out," the printer is physically detecting a cartridge but cannot read the chip. If it says "Ink cartridge cannot be recognized," there is likely a physical gap or debris preventing a flush connection. If the error persists across multiple new cartridges, the issue may lie with the gold pins on the carriage itself rather than the ink tanks.

How to Fix It

Follow these precise steps to reset the communication link and ensure a physical lock:

1. Power off the printer and unplug the power cord from the wall to clear the temporary volatile memory.
2. Open the scanning unit/cover. Wait for the printhead carriage to slide to the center.
3. Identify the problematic cartridge (e.g., PGI-280 Black or CLI-281 Color). Lift the cartridge out of its slot completely.
4. Inspect the copper contact pads on the back of the cartridge. Using a lint-free microfiber cloth dampened with a tiny amount of 90% isopropyl alcohol, gently wipe the gold contacts. Do not touch the ink nozzles on the bottom.
5. Inspect the pins inside the carriage. Ensure no small pieces of orange plastic packaging or adhesive residue are blocking the pins.
6. Reinsert the cartridge. Push it straight down firmly. You must hear a distinct, audible "click" as the locking tab engages. If the cartridge feels "spongy" or sits slightly higher than the others, it is not seated.
7. Close the cover and plug the printer back in.
8. When the "Ink has run out" message appears on the OLED screen, press and hold the Stop/Reset button (the red circle with a triangle) for exactly 5 to 10 seconds. This forces the printer to override the ink level monitor and bypass the "empty" warning, allowing you to print.

If That Didn't Work

• Hard Reset the Logic Board: Unplug the power cord and the USB cable (if connected). Hold the Power button down for 30 seconds to drain all capacitors. Plug it back in and attempt the Stop/Reset hold again. This clears stubborn "missing" errors caused by firmware glitches.
• Swap and Isolate: If you have another known-working cartridge of the same color, swap it in. If the error persists with a second new cartridge, the gold contact pins in the printer carriage are likely bent or contaminated. Use a can of compressed air to blow out the slot to remove any leaked ink that may have dried into a film over the pins.
• Check for Non-Genuine Chips: If you are using third-party remanufactured cartridges, the TS6420a may reject the chip's signature. Perform the "Stop/Reset" hold for 10 seconds. If a prompt appears asking if you want to continue using non-genuine ink, select "Yes" or "OK" using the arrow keys.
• Update Firmware: Use the Canon PRINT app or a computer to check for a firmware update. Sometimes a "missing" error is a known bug that Canon patches via a software update to improve chip compatibility.

Heads Up

• Avoid Over-Cleaning: Never use a pencil eraser or abrasive scrubbers on the cartridge contacts, as this can strip the thin gold plating and permanently kill the chip.
• Seal Integrity: Ensure the orange protective tape is completely removed from the top of the cartridge before insertion; any remaining adhesive can prevent the cartridge from clicking into place.
• Storage Warning: Always store spare cartridges upright in their original packaging. Storing them on their sides can cause ink to leak into the chip area, leading to immediate "missing" errors upon installation.
• Ink Mixing: Do not mix genuine Canon inks with third-party inks in the same machine, as the different chemical viscosities can cause the printhead to clog, which the printer may misinterpret as a cartridge error.