Apple Color LaserWriter 12/600 PS ation User Manual download pdf (Page 79)

95.08.23.11.29

Color LaserWriter 12/600 PS Basics & Theory 1–68

Photosensitive Drum Life Detection

Outline The printer determines the life of the photosensitive drum mathemati-

cally 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 rein-

stalled. 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 photocon-

ductor 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 detec-

tion is performed. See “Drum Separation” below.

The photosensitive drum thickness detection circuit is in the high-

voltage 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.

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Apple Color LaserWriter 12/600 PS ation User Manual Page 79

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