HP LaserJet 4 Service Manual - Page 279

Image Formation Troubleshooting Half Self-Test Functional Check The electro-photographic process can be subdivided into the following stages: • Cleaning (Physical and Electrostatic). • Conditioning (Primary Charge Roller). • Writing (Laser Modulation). • Development (Formation of the Toner Image). • Transfer (Charge to transfer the image to paper). The purpose of the Half Self Test Check is to determine which process is malfunctioning. Perform the test as follows: 1 Initiate an 05 SELF TEST. 2 Open or switch OFF the printer after the paper advances halfway through the printer (the leading edge of the paper should advance at least past the Transfer Charge roller). 3 Remove the Toner Cartridge. 4 Open the Toner Cartridge's drum shield to view the drum's surface. If a dark and distinct toner image is present on the drum's surface, assume that the first four functions of the electro-photographic process are functioning, and troubleshoot the failure as a transfer problem. If NO image is present on the photoconductive drum, perform the checks shown on the following pages. • The Drum Rotation Functional Check. • High voltage Power Supply Check. Troubleshooting 7-49