DIAGNOSIS The thermal print head is dirty or the pressure roller adjustment is off. Debris on the print head causes uneven heating.
FIX Turn the unit off and remove the tape cartridge. Dampen a cotton swab with isopropyl alcohol (90% or higher). Gently wipe the silver-colored thermal print head strip inside the machine. Let it dry completely for 2 minutes. Reinstall the tape and print a test label.
IF THAT DIDN'T WORK The print head pressure might be too light. With the tape out, locate the small silver pressure lever near the print head. Use tweezers to gently bend it *slightly* downward, about 1mm. This increases contact pressure.
HEADS UP Never use water or household cleaners on the print head. Do not scrub with abrasives. You will permanently scratch the delicate heating elements.