oki microline 620 printhead issues

old printhead... is very light and faint even after adjustments so decided to replace...
machine in warranty...

we got first printhead from oki... it wouldn't move from the left corner...just errorored out...
second printhead did the same...

threw old printhead in... machine printed like a champ... veryl light... and white spaces but printed like a champ...

any ideas would be appreciated....