Oce 3121 Technical & Service Manual page 248

Switching the DC developing bias ON and OFF
The DC developing bias is switched ON and OFF by the DC bias ON/OFF
signal (DCON). The signal comes from the DC control PBA .
The primary side of the main transformer (T101), on the power supply PBA,
is controlled by the CPU (Q605). When the DCON signal is sent to the power
supply PBA , the CPU (Q605) generates the DC bias control signal (BPWM).
This switches on the secondary side of the main transformer (T101), applying
the DC developing bias.
Limiting the DC Developing Bias to a Specific Voltage
When the DC developing bias is being applied, the CPU (Q605) on the power
supply PBA receives the application voltage from the voltage detection circuit.
Thus, the duty ratio of the BPWM signal is varied, ensuring that the DC output
voltage is maintained to a specific value.
Switching the AC developing bias ON and OFF
The developing AC drive circuit on the power supply PBA receives drive pulse
signals from the CPU (Q605). When the AC drive signal (ACON) is directed
from the DC control PBA to the AC drive circuit, the AC transformer (T400)
is switched ON. This supplements AC to the DC developing bias.
Application frequency: 1838 Hz
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Application voltage: 800 Vp-p
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Varying the DC Developing Bias
The density of the image is adjusted by varying the density correction curve
(DC developing bias).
During printing (printer function), the density is adjusted by fixing the density
correction curve. Then, varying the bias DC to maintain correct gradation.
To compensate for variations in the OPC, the control is carried out according
to a specific timing. (with AGS measurement to increase the developing bias).
502 TSM Océ 3121 Functional description