Gestetner B070 Service Manual page 983

DRUM UNIT
Grid Voltage (Vg) Adjustment
Then, the machine determines the corona grid voltage (Vg) that will be used during
copying. This is done as follows:
1. A Vd pattern is unexposed on the drum and the bias for the unexposed area is
adjusted.
2. The drum potential sensor reads the Vd potential.
3. Vd should be –800 ± 20V. If it is within this range, the current value of Vg will
be used for copying. If it is not within this range, - (Vd + 800)V is added to Vg,
and the process starts again from Step 1.
⇒
NOTE: VD Correction - As the development sleeve accumulates toner over time,
the gap between VD and VB decreases, which makes it easier for dirty
background to occur. To compensate for this, the machine increases the
target VD value to -850±20V when the number of copies exceeds the value
set with SP3903: VD Correction Counter (default: 200K). As a result, VD
increases and the VD-VB gap is maintained
⇒
4. If Vd cannot be adjusted to this standard within 5 attempts, Vg is set to the
value of SP2001-001 (default: –900V) and SC315 (Potential Sensor Calibration
Error 3) is logged.
LD Power Adjustment
Finally, the machine determines the laser diode power that will be used during
copying. This is done as follows.
1. The laser power is changed to the value needed to write a halftone pattern to
the drum.
2. The drum potential sensor reads the potential, Vh, from this pattern.
Vh: Standard halftone drum potential
3. Vh should be –260 ± 20V. If it is within this range, the current value of the laser
power will be used for copying.
• If it is not, the laser power changes by 5 units, and the process starts again
from step 1.
• The laser power cannot be adjusted within the range –70 to +185.
4. If Vh cannot be adjusted to this standard within 45 attempts, LD power is set to
the most recent value and SC316 (Potential Sensor Error 7) is logged.
ID Sensor Calibration (Vsg)
After power-on, Vsg (the ID sensor output from reading the bare drum) is set to
4.00±0.2V by changing the intensity of the light from the sensor shining on the
drum. This can also be done at any time with SP3001 002 (ID Initial Setting – Vsg).
⇒
NOTE: If the ID sensor output cannot be adjusted to the standard, then after 20
seconds SC353 or SC354 is issued. Toner supply during copying will then
be controlled using the TD sensor only, until the machine is repaired.
B070/B071
CÓPIA NÃO CONTROLADA
6-68
CÓPIA NÃO CONTROLADA
Rev. 06/2003
SM