Ricoh A220 Service Manual page 73

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15 July 1996
1.3.5 V
Correction
D
[–V]
Drum
Potential
–770
Dark
The drum potential just after the black pattern (V
Dark Potential) tends to lower during drum life due to a decrease in the
drum's capacity to carry a charge.
To check the actual V
V
pattern (Black) stuck on the bottom side of the exposure glass bracket is
D
exposed on the drum.
The main control board measures V
adjusts it to a target value by adjusting the grid bias voltage (V
On the other hand, there is a change of the drum residual voltage (V
that the target V
D
Target V
Value: V
D
The adjusted grid bias voltage (V
process control data initial setting.
V
D
V
R
New Drum
Original Density
, the first scanner moves to the home position and the
D
voltage is compensated as follows:
= V
+ (–770)
D
R
GRID
V
Pattern
D
V
Compensated
D
After many copies
Light
A176D506.wmf
Pattern) is exposed (V
D
through the drum potential sensor and
D
) is kept in memory until the next
2-7
PROCESS CONTROL
Exposure
Glass
A176D505.wmf
V
R
:
D
).
GRID
), so
R

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