Gestetner A294, Service Manual

Page: 89 / 600

DRUM UNIT
SM 2-39 A294/A295
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Drum Potential Sensor Calibration
The drum potential sensor [A] detects the electric potential of the drum surface [B].
Since the output of the sensor is affected by environmental conditions, such as
temperature and humidity, the sensor needs recalibration at times. This is done
during process control initial setting.
The charge/bias/grid power pack [C] has two relay contacts. Usually RA2 grounds
the drum. However, to calibrate the sensor, the BCU switches RA2 and RA1 over,
which applies the power pack output voltage to the drum shaft [D].
The machine automatically calibrates the drum potential sensor by measuring the
output of the sensor when –200 V and –700 V are applied to the drum. From these
two readings, the machine can determine the actual drum potential from the
potential sensor output that is measured during operation. To prevent toner
attraction to the drum during calibration, –200 V and –700 V are also applied to the
development rollers.
During calibration, if the rate of change in drum potential sensor response to
applied voltage is out of the target range, an SC310 or SC311 is logged and auto
process control turns off. The V
G
and LD power adjustments are skipped; V
G
is set
to the value stored in SP2-001-01, and LD power is set to the values stored in
SP2-103.
V
SG
Adjustment
This calibrates the ID sensor output for a bare drum to 4.0
±
0.2 V. It does this by
changing the intensity of the light shining on the drum from the sensor. This is done
automatically during process control initial setting, and it can also be done
manually with SP3-001-002.
If the ID sensor output cannot be adjusted to within the standard, an SC353 or 354
is logged and the light intensity is set to the previous accepted value.
–200/–700
R A 2
R A 1
[A]
[B]
[C]
[D]
CÓPIA NÃO CONTROLADA
CÓPIA NÃO CONTROLADA