Canon GP160, Service Manual

Page: 105 / 797

COPYRIGHT © 1999 CANON INC. CANON GP160 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 6 IMAGE FORMATION SYSTEM
6-7
V. DEVELOPING BIAS CONTROL
A. Outline
The circuit shown in Figure 6-501 is the circuit which controls the developing bias in
the DC controller PCB. It’s principal functions are as follows:
• Developing bias AC ON/OFF control
• Developing bias DC ON/OFF control
• Developing bias DC constant voltage control
B. Operation
The developing bias control is performed by the DC ON/OFF signal (DVDUP) and
the AC ON/OFF signal (DVACON), which are output from the DC controller PCB’s CPU
(IC 301).
When DVDUP*=0 is output from the CPU, developing bias DC is applied by power
being supplied to the DC bias generation circuit,. And, when the DVACON signal is out-
put from the CPU, AC bias is generated.
Due to the CPU outputting these signals at designated times, developing bias is gen-
erated and applied to the developing cylinder.
Furthermore the output voltage from the DC bias generation circuit undergoes con-
stant voltage control by being returned to the comparison circuit.
Figure 6-501
AC bias
generation
circuit
DC bias
generation
circuit
DC bias
detection circuit
+24V
[1] DVACON
Compara-
tive circuit
[2] DVDUP
DC controller PCB
CPU
(IC301)
Photo-
sensitive
drum
Bias drive
circuit
JH402
[1] DVACON: AC bias drive signal
[2] DVDUP: DC ON/OFF signal