Canon CLC 1120 Service Manual page 569

CHAPTER 13 TROUBLESHOOTING
9 Checking the Surface Potential System
If an image fault has occurred, you must be sure if the cause is in the static latent image
formation block (including the photosensitive drum and the potential control system) or the
developing/transfer system. To that end, the surface potential must be checked as follows:
a. Checking the Surface Potential
1) Select FUNCTION>DPC>DPC in service mode (for potential control).
2) Check the following using DISPLAY>DPOT in service mode.
Screen display
V00-500 430 to 570
V00-700 600 to 800
VFF-500 50 to 150
VFF-700 100 to 200
3) If the value is not as indicated, make a zero-level check.
b. Zero-Level Check
You can make use of a zero-level check to see whether the surface potential control circuit is
good or not, thereby finding out whether the level shift circuit of the DC driver PCB and the
potential measurement unit is good or not.
Reference:
A zero-level check is designed to find out whether the CPU reads the surface potential of the
drum as '0' when it is 0 V.
A zero-level check may be either of the following two:
Method 1: to find out whether the level shift circuit on the DC driver PCB is good or not
Method 2: to find out whether the potential measurement circuit is good or not
Method 1
1) Remove the rear cover.
2) Turn on the power switch, and wait until the copier is in standby state.
3) Disconnect the connector J4 (J440) of the potential measurement PCB.
4) Short the check pins J1040-1 and -2 on the DC driver PCB with a jumper wire.
5) Check to make sure that the reading of DISPLAY>DPOT>DPOT is 80 ± 30 V in service
mode.
If yes, the part is normal. Go to step 8).
6) Measure the voltage between GND CP and CP4 of the DC driver PCB to see if it is 0.49 ± 0.1
V.
If no, suspect a fault in the level shift circuit on the DC driver PCB. If yes, suspect a fault in the
A/D converter on the CPU PCB.
7) Turn off the power switch, and disconnect the jumper wire; then, connect the connector.
8) Mount the rear cover, and turn on the power switch.
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COPYRIGHT © 1999 CANON INC.
Guide
CANON CLC1120/1130/1150 REV.0 MAR. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)