Canon NP6512 Service Manual page 100

CHAPTER 4 IMAGE FORMATION SYSTEM
d. Primary Charging Roller Bias Application Voltage Level and Scanning Lamp Activa-
tion Voltage Level Automatic Correction Control (APVC, ALVC control)
The quality of copy images can vary in relation to changes in latent static images, which are
affected by the following:
• Changes in the sensitivity of the drum
• Changes in the amount of charging of the primary charging roller
These changes occur because of changes in the installation environment (temperature, humid-
ity) or deterioration, wear, and dirt of related parts.
In the machine, these changes tend to increase the light area potential (VL) and the dark area
potential (VD).
To correct these changes, the level of voltage applied to the primary charging roller is corrected
(APVC control) and, at the same time, the level of the voltage used to turn on the scanning lamp is
corrected (ALVC control). These control mechanisms serve to ensure a specific degree of light area
potential (VL) and dark area potential (VD) at all times.
The following indicates the timing of auto correction and the flow of operation:
<Timing>
At power-on, During INTR
<Flow>
A voltage of -1376 V is applied to the primary charging roller for about 1.3 sec.
The current at the time is detected by the current detection circuit, and is communicated to the
microprocessor (Q900) on the composite power supply PCB.
The microprocessor (Q101) on the DC controller receives the current level from the compos-
ite power supply, and determines the voltage used to activate the scanning lamp and the
voltage of the primary charging roller bias.*
* The control mechanism uses the return current stored in memory in advance by the DC
controller PCB and the correction table for activation voltage/application voltage.
Caution:
If you have replaced the composite power supply PCB, be sure to enter the APVC value
indicated on the composite power supply PCB using service mode (Nos. 34, 35). Then, be
sure to execute 'U7' in user mode (installation/drum replacement mode).
4-8
COPYRIGHT © 1999 CANON INC. CANON NP6512/6612/7120/7130/7130F REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)