Faint printing
print ribbon is simply worn out and needs to be replaced.
No printing
connect the print head cable or replace the ribbon.
Paper jamming
you have the wrong type of paper or the wrong size paper.
Line across the page
You might be able to loosen the stuck pin, or you might need a new print head.
Several letters have missing dots
Replace print head
printing dark and clear on one side, light on the other
adjust the platen