These are thermal printers.
They use a heated strip that spans the width of the ticket.
As the paper moves different parts of the element is heated.
The observation is that it appears that the entire width of the ticket is missing elements vs spots.
I am not familiar with the specifics of the printer but have worked with a variety of POS printers over the years.
The slow ones use a single heating element, while the higher speeds (which this likely is) has several elements on a roller.
I would speculate that either one of these elements is dead or extremely dirty.
If its dead you can likely replace the roller but there should be enough of them on the secondary market that its likely cheaper to just replace the printer.
Here is the excerpt from one of the manuals..... it says poor paper can be a cause but as its the same paper for both I don't think this is a factor.
A thermal printer not printing clearly can be due to several reasons, including a dirty print head, low-quality paper, or incorrect settings. To troubleshoot, start by cleaning the print head, ensuring you're using the correct type of thermal paper, and checking your printer settings. If the problem persists, you may need to adjust print speed or consider replacing the printer.
Here's a more detailed breakdown of potential causes and solutions:
1. Dirty Print Head:
Problem:
Dirt, dust, and residue from the printing process can build up on the print head, interfering with the heating process and causing unclear prints.
Solution:
Turn off the printer and unplug it.
Open the printer cover and locate the print head.
Use a soft, clean cloth dampened with isopropyl alcohol to gently wipe the print head.
Allow the print head to dry completely before turning the printer back on.
2. Low-Quality or Incompatible Paper:
Problem:
Using low-quality or incompatible thermal paper can lead to poor print quality, including streaks, smudges, or faded text.
Solution:
Ensure you're using the correct type of thermal paper for your printer model.
Use thermal paper that's designed for direct thermal printing (if your printer uses that technology).
Consider using higher-quality thermal paper for better print clarity.
3. Incorrect Printer Settings:
Problem:
Incorrect print settings, such as print speed or print darkness, can affect the clarity of your prints.
Solution:
Consult your printer's user manual for instructions on adjusting print settings.
Try adjusting the print speed or print darkness settings to see if it improves the print quality.