If you are having trouble with your Ninja Master Prep QB900B ,start by going to: https://www.ifixit.com/Wiki/Ninja_Master_Prep_QB900B_Troubleshooting
Background and Identification
The Master Prep is a 400 watt multipurpose blender released between 2009 and 2013. Produced by Ninja, it features a removable blender which owes to it's convenience. The removable blender allows it to be easily swapped between the 16 oz. and 48 oz. bowl and pitcher. The Master Prep has mixed reviews claiming that while it is convenient it is poorly made.
Since the blender top can be removed, the device is quite easy to repair. This is helpful since it is common for the device to malfunction.