Ricoh G148, Service Manual

Page: 460 / 537

1. The drum motor starts.
2. The grid voltage, development bias, and laser power are set to the default values that would be used
if process control was disabled. These are as follows:
• Development bias is set to the value stored in SP2201-001
• Grid voltage is set to the value stored in SP2001-001
• Laser power is set to a fixed value
Grid Voltage (Vg)
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 exposed on the drum (if developed with toner, this will be black).
Vd: Drum potential in black areas after exposure.
2. The potential sensor reads the potential, Vd, from this pattern.
3. Vd should be –800
±
10V.
• If it is within this range, the current value of Vg will be used for copying.
• If it is not in this range, -(Vd + 800)V is added to Vg, and the process starts again from step 1.
4. If Vd cannot be adjusted to this standard within 5 attempts, Vg is fixed to –1,000V and SC312
(Potential Sensor Calibration Error 3) is logged.
LD Power
Finally, the machine determines the laser diode power that will be used during copying. This is done as
follows.
The laser power is changed to the value needed to write a halftone pattern to the drum.
1. The potential sensor reads the potential, Vh, from this pattern.(Vh: Standard halftone drum potential)
2. Vh should be –300
±
20 V.
• 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 3 units, and the process starts again from step 1.
3. The laser power cannot be changed by more than ± 60 units.
4. If Vh cannot be adjusted to this standard within 25 attempts, LD power is set to the most recent value
and SC314 (Potential Sensor Calibration Error 4) is logged.
ID Sensor Calibration (Vsg)
After power-on, Vsg (the ID sensor output from reading the bare drum) is set to 4.00 ± 0.2 V 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).
The calibrated ID sensor output will be used for calibrating the TD sensor (described below).
Drum Unit
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