What are the reasons for text isn't obvious? How to deal with it?

What are the reasons for text isn't obvious? 

How to deal with it?

The reason:
The toner, magnetic roll developing voltage and carbon power is low, effect of photosensitive is poor .
The resolution is doesn't meet the printer requirement.
The printer has been working too long and it's tired.

Solution:
shake out the toner cartridges, if the printing effect is not improved, please replace the toner cartridges.
Test the resolution and meet the printer requirements.
Arrange the printing interval to restore the performance of the light-sensitive drum.
Clean the photoelectric components in the printer.