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October 9th, 1995
5. Shading Error
Symptoms:
A shading error occurs when one of the following conditions occurs.
•
The difference in black level based on CH1 of the DAC setting between
even and odd pixels is not within ± 1.
The black level based on CH2 of the DAC setting is not within 3 ± 1.
•
•
The minimum hold value of the auto gain control circuit in the SIP3 is
not over 128.
•
The value of CH4 for the DAC cannot be adjusted.
Possible Causes:
•
A mirror is out of position.
•
Misalignment.
•
SCU damaged.
•
SBU damaged.
•
The lamp is defective.
•
The shading seal is dirty.
Procedure:
Is there any problem with the lamp?
Yes
No
Is the shading seal dirty?
Yes
Replace the ADF cover.
Replace the lamp.
Note: The read signal goes to the SCU through the MBU, but the MBU
does not do any image processing. Therefore the MBU probably
does not have a problem. However, if the problem is not solved even
after replacing the SCU, try changing the MBU.
TROUBLESHOOTING PROCEDURES
No
Are all the mirrors installed properly?
Yes
No
Reseat the mirror.
Does the SBU generate the correct signals?
Yes
No
Replace the optical unit.
Replace the SCU.
6-11
TROUBLESHOOTING
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