A method and apparatus can, while operating a printing device in a test mode, supply a changed transfer field to a marking material transfer device. The changed transfer field is less than or more than the standard transfer field. The method and apparatus disable operations of other marking material transfer devices of the printing device to isolate the marking material transfer device. Further, the method and apparatus compare the actual amount and/or spatial distribution of marking material transferred to a recipient surface (to which the first marking material transfer device transfers the marking material) against a predetermined standard. Then, if the actual amount of marking material transferred to the recipient surface is different than the predetermined standard, the method and apparatus can identify the first marking material transfer device as being a potential source of printing defects.