Service manual
DEVELOPING UNIT
2-G-6
2 UNIT EXPLANATION
[7] Gradation Correction Control
Gradation correction control is performed by the TCSB
(toner control sensor board), M2 (drum), M3 (develop-
ing), and so on. These parts are controlled by the
PRCB (printer control board).
1. Operation
The gradation characteristics of the toner density
versus exposure amount at the image forming
section (drum area) are detected to obtain a lin-
ear relation between the image density on a doc-
ument and the copying image density (toner
density).
(1) Method
Exposure is performed with the laser PWM var-
ied in several steps, and development is per-
formed at the toner transfer sleeve speed
obtained by Dmax correction.
Next, each density is read by γ sensor (PD2) on
the TCSB to detect the gradation characteristics
of image density.
The gradation characteristics obtained here are
used as the values for correcting the laser expo-
sure amount.
(2) Timing
a) When the fixing temperature is lower than
50°C at power ON.
b) At the end of job after every 20,000 copies.
2. Signals
a. PRCB Input signals
(1) γ SIG/MONI (TCSB to PRCB)
Output voltage from the γ sensor (PD2) on the
TCSB. This signal monitors the light reflected by
the drum surface (without toner).
The voltage applied to the gradation detection
LED is corrected by γ/Dmax LED Vref so that the
output voltage becomes 4.5V (calibration).
Reference voltage: 4.5V
<Timing>
Before gradation correction.
PRCB
DCPS2
DCPS1
DPSB
DPS
TCSB
24VDC
24VDC
PGND
12VDC
5VDC
SGND
M2 CONT
M2 F/R
SGND
M2 EM
M3 CONT
M3 CLK
M3 EM
DPS DRIVE A
DPS DRIVE B
DPS ANG 1
DPS ANG 2
DPS ANG
AGND
5VDC
MS2 MS1
M2
M3
/Dmax LED Vref
LED CONT
SIG/MONI
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