2. Controlling the Transfer Charging
Roller Bias
The transfer charging roller bias is controlled
by the CPU (Q605) on the composite power sup-
ply PCB according to instructions from the DC
controller PCB.
a. Switching between Bias Types
The aforementioned bias types are switched
based on combinations of the transfer output
mode 0 (HVTM0) and the transfer output mode 1
(HVTM1) from the DC controller PCB. (See Table
3-501.)
Table 3-501
b. Turning ON and OFF the Cleaning Bias
When the cleaning bias drive signal
(TREVON) of the composite power supply PCB
goes ‘1’, the secondary side of the main trans-
former (T101) turns ON to apply a cleaning bias
(negative) to the transfer charging roller.
The timing at which the cleaning bias is
applied is determined by serial communication
data exchanged with the DC controller PCB.
c. Turning ON and OFF the Transfer Charging
Roller
The transfer charging roller bias is turned ON
and OFF by the transfer bias control signal (TFW-
PWM) and the transfer bias ON signal (TFWON).
When the TFWON signal goes ‘0’, the trans-
former T502 turns ON.
3. Adjusting the Transfer Charging
Roller Bias
If image faults occur as a result of an incorrect
transfer charging roller bias, the transfer bias may
be adjusted under ‘TRN-1’, ‘TRN-2TS’, or ‘TRN-
20L’ in service mode (*3*; ADJUST).
An image fault may be any of the following:
q
Fogging is noted in the margin along the trail-
ing edge because of stray toner.
w
The density of copies increases every 94
intervals (approx.) when making half-tone
copies (entire surface).
In the case of
q
, increase the setting; in the
case of
w
, decrease the setting.
• Use TRN-1 to adjust the transfer bias for
copying on the 1st side.
• Use TRN-2ST to adjust the transfer bias for
copying on the 2nd side of a two-sided
copy.
• Use TRN-20L to adjust the transfer bias for
copying on the 2nd side of an overlay copy.
3–65
COPYRIGHT © 1996 CANON INC. CANON GP215/200 REV.0 JULY 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)
3. OPERATIONS AND TIMING
HVTM0
HVTM1
Bias type
0
0
Cleaning bias
1
0
Transfer bias
0
1
Reference bias
1
1
Sheet-to-sheet bias
