i put in a new tape but it keeps saying 'out of tape' on the screen. it's full.

Diagnosis

The "Out of Tape" error on the Nelko P21 is rarely about the actual quantity of tape remaining in the cartridge; rather, it is a sensor failure caused by a misalignment between the tape head and the internal detection mechanism. The P21 uses a physical tension sensor to confirm the tape is feeding correctly. If the tape is not seated perfectly flush against the drive gear, or if there is a microscopic fragment of adhesive residue on the sensor eye, the machine assumes the roll is empty because it doesn't detect the expected resistance or movement. Another common cause is the "leading edge" problem. If the tape has slipped slightly out of the guide slot or is curled backward into the cartridge housing, the printer cannot "grab" the tape to move it forward. Because the motor spins but the tape doesn't advance, the onboard logic triggers the "Out of Tape" alert to prevent the print head from overheating while printing on air. You can confirm this by opening the compartment and checking if the tape is taut or if there is a visible gap between the tape and the output slot.

How to Fix It

To resolve this and force the sensor to recognize the new cartridge, follow these precise steps:

1. Power down the P21 completely by holding the power button until the screen goes dark.
2. Open the tape compartment cover and remove the tape cartridge entirely.
3. Inspect the tape roll. Ensure the tape is wound tightly and that the leading edge is protruding exactly 2-3mm from the guide slot. If the tape has receded into the plastic housing, gently pull it forward with your fingernail until it is flush with the edge.
4. Locate the small gold-plated contact points on the cartridge and the corresponding pins inside the machine. Use a dry cotton swab or a microfiber cloth to wipe these contacts to remove any oils or dust that could interfere with the electronic handshake.
5. Re-insert the cartridge, ensuring it clicks firmly into place. Do not just set it in; apply firm pressure until you feel the locking mechanism engage.
6. Close the cover and power the device back on.
7. Perform a "Feed" operation via the app or the physical button to advance the tape by 10mm. This resets the sensor and clears the error message.

If That Didn't Work

• Hard Reset the Sensor: With the machine on and the tape installed, press and hold the power button for 10-15 seconds. This forces a hardware reboot of the sensor array, which can clear "ghost" errors that persist even after a tape change.
• Check for Adhesive Buildup: Open the compartment and look at the rubber roller (the platen). If there is a buildup of sticky residue from previous labels, the tape may be slipping. Clean the roller using a small amount of 70% Isopropyl Alcohol on a cotton swab. Rotate the roller manually to clean the entire circumference.
• Verify Tape Compatibility: Ensure you are using the correct P21-specific thermal tape. If you are using a third-party cartridge that is slightly off-spec in thickness (even by 0.1mm), the tension sensor will trigger the "Out of Tape" error because the fit is too loose.
• Clear the Print Head: Use a can of compressed air to blow out the print head area. A tiny piece of peeled-off label backing can sometimes lodge itself in the sensor path, tricking the machine into thinking the tape has run out.

Heads Up

• Never pull the tape out of the cartridge by more than half an inch, as this can cause the tape to telescope or jam, triggering the same error.
• Avoid touching the thermal print head (the small heating element) with your fingers, as skin oils can cause "voids" or white streaks in your labels.
• Always ensure the tape cover is snapped shut completely; if the lid is slightly ajar, the sensor will not engage, and the machine will report a tape error.
• Store your spare tape cartridges in a cool, dry place. High humidity can cause the adhesive to seep, which gums up the internal gears of the P21 and leads to feeding errors.