Potential Measurement Circuit - Canon NP6251 Service Manual

CHAPTER 4 IMAGE FORMATION SYSTEM
Caution:
If the measurement dose not fall within the tolerance after eight tires, '1' is indicated
to 'LLMT' (upper limit flag of lamp activation voltage) in service mode (*1*; display
mode).
c. Controlling the Developing Bias
The light area potential (V
surface potential of the drum occurring when the scanning lamp is turned on based on
the last intensity adjustment signal generated during V
The DC controller PCB uses the measurement to control the developing bias DC
level control signal (DEVDC) to control the DC bias applied by the high-voltage
transformer on the developing cylinder.

3. Potential Measurement Circuit

Figure 4-103 is a cross sectional diagram of the potential sensor, and Figure 4-104
is a block diagram of the potential measurement circuit.
The drive signal from the sensor drive circuit drives the chopper so that the electrode
of the sensor assembly can detect the drum surface potential.
The measurement signal of the drum surface signal is amplified by the pre-amplifier
circuit, and is sent to the drum surface potential detection circuit.
The drum surface potential detection circuit converts the AC signal to an AC signal,
and sends it to the level shift circuit through the 1/300 transformer circuit.
The output signal (analog) of the level shift circuit is sent to the microprocessor on
the DC controller PCB.
a. Making Checks
LED1 Activation
LED1 is normally on when the main motor rotates.
If it does not turn on, you may suspect a fault in the potential measurement unit.
Reference:
When LED1 is on normally, the potential sensor is operating normally.
Caution:
The sensor and the potential measurement PCB are adjusted to a high precision as
a pair, and cannot be adjusted in the field. They are treated as a single entity
service part.
4-4
COPYRIGHT © 1997 CANON INC.
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) for the developing bias is measured in terms of the
L2
CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
control.
L1