Canon CLC 1120 Service Handbook page 56

CHAPTER 2 STANDARDS AND ADJUSTMENTS
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
V00-700
VFF-500
VFF-700
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 100 ± 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.
2-38
Guide
430 to 570
600 to 800
50 to 150
100 to 200