Ricoh FT8680, Service Manual

Page: 35 / 389

1.3.8 VL Correction
Dirty optics and/or exposure lamp deterioration decreases the intensity of the
light that reaches the drum. In addition to this, the drum sensitivity also
changes during the drum’s life. These factors change the drum potential just
after white pattern exposure (V
L
: Light Potential).
To check the actual V
L
, the first scanner moves to the home position and the
V
L
pattern (White) stuck on the bottom side of the exposure glass bracket is
exposed on the drum.
The main PCB measures the V
L
through the drum potential sensor and
adjusts it to a target value by adjusting the exposure lamp output.
The residual voltage change also affects V
L
, so that V
L
’s target voltage is
compensated as follows:
Target Value of V
L
: V
L1
= Vr + 50 – 10 N -15 M (volt)
NOTE: N is the setting for the exposure lamp adjustment in the SP mode.
M is the setting for the Latent Image Adj. in the SP mode.
The adjusted exposure lamp output control value (PWM value) is kept in
memory until the next initialization.
If the target value cannot be achieved within the exposure lamp output
control range, the copier indicates the system error on the CRT screen. The
copier tries the V
L
check again after the SC reset. Even if the second V
L
adjustment fails, no SC condition is displayed. The previous exposure lamp
output control data will be used in this case.
V
L
Pattern
A171D508.wmf
Drum
Potential
Original Density
Dark Light
V
L
Vr
A171D521.wmf
31 July 1995 PROCESS CONTROL
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