Panasonic PANAFAX DF-1100, Service Manual

Page: 216 / 333

Panasonic DF–1100
6–20
ABC Circuit
This circuit consists of IC111, IC90, C211 (C203), R206 (R200) and R211 (R201). Its function is to prevent
deterioration of picture quality due to dirt on the document or degrading of the luminous energy of the Xenon
Lamp light source. The picture signal from the CCD is amplified in IC4 (CCD PCB) and IC111 and input to
IC90, where it is converted from analog to digital and the shading is corrected. When the signal exceeds
+3.0V as the result of this amplification and correction, capacitor C211 (C203) is charged through R206
(R200). This charging voltage lowers the level of the picture signal input to IC111. When the picture signal
voltage rises, this charge voltage becomes higher. When the picture signal level lowers due to the back-
ground color, etc., of a transmitting document, the voltage of the charged capacitor C211 (C203) is dis-
charged through R211 (R201). Consequently, the output of the ABC circuit is kept constant to maintain the
picture quality, regardless of changes in the CCD output level.
+12V
CCD Output
ABC Circuit Output
+5V
R206
(R200)
C211
(C203)
R211
(R201)
IC4
IC111
32(31)
36(29)
19(21)
IC112
IC90
M86072
Control
Circuit
41(24)
39(26)
40(25)
CCD PCB
VOUT1
(VOUT2)
0V
3.0V
0V
Shading Correction Circuit
The Shading Correction Circuit, included in IC90, is provided to correct for reduction in lamp intensity around
the optical lens and lamp intensity distortion due to shading of each bit. This circuit scans the reference white
on the transmitting document plate immediately before the document reaches the scanning position and
writes a compensation value according to the distortion of the waveform, at the time, into the S–RAM
(IC103).When the actual picture signal is input, the circuit corrects the picture signal shading, according to
this compensation value. This shading is carried out for each page during transmission or copy.
Offset Control Circuit
The Offset Control Circuit consists of IC112, IC90 and IC4 (CCD PCB), and controls the black level of the
CCD output to be at 0V by using the IC4 (CCD PCB).
Picture Signal Binary Coding Correction Circuit
The Picture Signal Binary Coding Correction Circuit is included in IC90. It is used to obtain a binary coding
signal which is a corrected picture and error diffused signal of a false halftone signal, which is detected from
a shaded picture signal.