Checking The Surface Potential Control System - Canon iR8500 Service Manual

CHAPTER 6 TROUBLESHOOTING

2.7.11 Checking the Surface Potential Control System

a. Outline
If an image fault occurs, it is important to find out if the cause is in the latent image for-
mation block (including the photosensitive drum and the potential control system) or in the
development/transfer system, requiring a check to see if the surface potential is appropriate.
The service potential may be checked in service mode.
b. Disabling Auto Control
As a means of finding out if the corona current control, lamp intensity control, or devel-
oping bias control mechanisms is faulty, the auto control mechanism may be disabled (here-
after, "non-auto control mode").
In addition, non-auto control mode may be made use of as an emergency remedy in the
event a fault occurs in the auto control mechanism.
1. Procedure
1) Make the following selections in service mode, and enter '0':
COPIER>OPTION>BODY>P0-CNT; then, press the OK key.
2) Press the reset key twice.
When non-auto control mode is selected, all settings for corona current con-
trol, intensity control, and developing bias control will automatically be set
to standard settings stored in ROM.
2. Making Use of Non-Auto Control Mode
Use it to find out if the cause is on the input side or on the output side of the microproces-
sor on the DC controller PCB when an image fault occurs.
If any improvement is noted in non-auto control mode, a fault may be suspected in the
potential measurement unit or the DC controller PCB.
c. Zero-Level Check
A "zero-level check" may be used as a means to find out whether the surface potential
control circuit is good or not.
In a zero-level check, a check is made to find out whether the microproces-
sor indicates 0 V when the drum surface potential is 0 V.
REF.
Using a zero-level check, the microprocessor on the DC control PCB and the measure-
ment unit may be checked.
In method 1, the condition of the level shift circuit on the DC controller PCB may be
checked while in method 2 the potential control circuit may be checked.
1. Method 1
1) Turn off the power switch.
2) Short J522-1 and -2 on the DC controller PCB with a jumper wire, and disconnect
connector J3 of the potential control PCB.
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COPYRIGHT© 2001 CANON INC. 2000 2000 2000 2000 CANON iR8500/7200 REV.1 AUG. 2001