Panasonic Facsimile UF-590, Service Manual

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6.2.3 Picture Signal Scanning Block
The image data read by the optical unit is input to the CCD mounted on the CCD PC Board, then
transferred to the SC PC Board after the optical information is converted into an electrical signal by the
CCD. The following shows a block diagram of the picture signal scanning circuit. This picture signal
scanning circuit consists of (1) ABC circuit, (2) shading correction circuit, (3) offset control circuit, (4) picture
signal binary coding correction circuit and (5) reducing circuit.
ABC Circuit
This circuit consists of IC28, IC30, C175, R288 and R285. 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 IC28 and input to IC30, where it is converted
from analog to digital and the shading is corrected. When the signal e5V as the result of this
amplification and correction, capacitor C175 is charged through R288. This charging voltage lowers the
level of the picture signal input to IC28. When the picture signal voltage rises, this charge voltage
becomes higher. When the picture signal level lowers due to the background color, etc., of a transmitting
document, the voltage of the charged capacitor C175 is discharged through R285. Consequently, the
output of the ABC circuit is kept constant to maintain the picture quality, regardless of changes in the
CCD output level.
W
B
1728 bit
Effective Scan Width
CCD
TCD 1208P
Differential
Amplifier
CCD PC Board SC PC Board
CCD
Drive
Circuit
Delay
[SC]
IC30
MN86075
IC3
DZAC000273