Please check the following points to solve the problem:

NOTE: Illustrations shown below are from a representative product and operating system, and may differ from your Brother machine and operating system.

1. Make sure toner save mode is off in the control panel or the printer driver. Click here to see the details of how to change the toner save mode setting.
   
   
2. Check the print resolution. If Fine (2400 dpi class) is in use, change it to Normal (600 x 600 dpi) as described below. 
   
   For Windows printer driver:
   
   
   1. Open Printing Preferences. Click here to see the details of how to open Printing Preferences.
   2. Click the Basic tab and choose Normal (600 x 600 dpi) for Print Quality, and click Apply => OK.
      
      
      
   For Windows BR-Script printer driver:
   
   
   1. Open Printing Preferences. Click here to see the details of how to open Printing Preferences.
   2. Click Advanced....
   3. Choose Normal (600 x 600 dpi) for Print Quality in Printer Features, and click OK.
      
      
      
   For Mac OS X CUPS printer driver:
   
   
   1. Open the Print dialog. Click here to see the details of how to open Print dialog.
   2. Choose Print Settings from the pane pop-up menu.
   3. Click the Basic tab and choose Normal (600 x 600 dpi) for Print Quality.
      
      
      
   For Mac OS X BR-Script printer driver:
   
   
   1. Open the Print dialog. Click here to see the details of how to open Print dialog.
   2. Choose Printer Features from the pane pop-up menu.
   3. Choose General 1 (Set 1 for Mac OS X 10.4) for Feature Sets and choose Normal (600 x 600 dpi) for Print Quality.
      
      
      
      
3. If you use a Windows printer driver, choose the Improve Thin Line option and the Improve Pattern Printing option as described below.
   
   
   1. Open Printing Preferences. Click here to see the details of how to open Printing Preferences.
   2. Click Settings... from the Basic tab.
   3. Check the Improve Thin Line option and the Improve Pattern Printing option, and click OK.
      
      
      
   4. Click Apply => OK.