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Color LaserWriter 12/600 PS
Basics & Theory
1�68
Photosensitive Drum Life Detection
Outline The printer determines the life of the photosensitive drum mathematically by tracking page count. When a new photoconductor cartridge is installed, the EEPROM on the DC controller board logs the current page count of the printer. This value becomes the starting page count for that photoconductor. During each subsequent print, the controller compares the running page count against the starting page count stored in EEPROM. If the difference between the two values reaches a prescribed number, the controller determines that end of life has occurred and instructs the I/O controller to report the appropriate alert to the status panel. Only new cartridges initialize page count. Otherwise, the printer would recognize as new any used cartridge that had been removed and reinstalled. This safeguard is achieved by storing a second value in EEPROM, the thickness of the photosensitive drum. Note: Before replacing the DC controller board, you must download these values (see Chapter 2). If you are installing a new photoconductor and there is a chance that the old one will be reinstalled, as a troubleshooting measure for example, you must also download these values. Drum Thickness Detection The thickness of the photosensitive drum is detected upon power-on, door-open, and each time a certain number of prints is reached. Drum thickness is detected by measuring the discharged current value after charging by the primary charging roller to the photosensitive drum. For correct measurement of the current value, the photosensitive drum and the transfer drum are separated from each other and the thickness detection is performed. See �Drum Separation� below. The photosensitive drum thickness detection circuit is in the highvoltage power supply board. After the power is turned on and the main motor is turned on, the drum press solenoid (SL7) is turned on and the photosensitive drum and the transfer drum are separated. Then the drum motor is turned on, the primary charging DC voltage drive signal (/HV1DC1) and the primary charging AC voltage drive signal (/HV1AC1) are set to �L,� the primary charging AC voltage select signal (/HV1AC0) is set to �L,� and the primary charging DC voltage select signal (/HV1DC0) is set to �H� to apply the primary charging voltage to the photosensitive drum.
95.08.23.11.29
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