Slide Scanner Repair Manual Diagnostics and Troubleshooting
147
IPT Scanner Tests Descriptions
Motion and Color Registration Test
Motion/Color registration is a single test using color fringes on the edges of the chevron
section of the GMT target. Test results highlight opto-mechanical misalignments and
irregularities in the carriage’s transport motion.
Typically, a scanner which fails color registration, fails because the Peak Red minus Blue
(R-B) Misalignment exceeds the test specification. The misregistration can be thought of as
having two sources: static and dynamic. The static misalignment is the constant or DC
misalignment throughout the image. The dynamic or AC misalignment is the variation in the
misalignment up and down the leadscrew. The peak misregistration is a function of the
dynamic misalignments riding on top of the static.
The test provides diagnostic information about the sources of the misregistration. The
operator must look at the size and nature of the various contributions to determine if the
problem can be corrected.
Static (Color Registration)
Total mean or static color registration error is listed in test results as the Mean Offset and
displayed in units of pixels. The test breaks the static misalignment into two pieces, vertical
and horizontal, which are tied to two primary causes, each of which can be corrected out by a
step in the manufacturing or repair process.
Mean Vertical
The Mean Vertical offset is typically caused by errors in aspect ratio, i.e. the vertical and
horizontal magnifications are not equal. Vertical magnification is a function of the lead
screw pitch, and the horizontal magnification is a function of the optical setup. If the Mean
Vertical Offset is a significant portion of the Peak Misalignment, the operator can adjust
the horizontal magnification to match the horizontal to the vertical magnification, using the
Magnification and Focus Target and an adjustment procedure (See MAG and Focus
Adjustment procedures). This test results suggest the Best Mag Time Change in
microseconds to make when adjusting the magnification to optimize the aspect ratio and
eliminate the Mean Vertical Offset.
Mean Horizontal
The Mean Horizontal offset is typically caused by CCD Tilt. The test provides a
measurement of that tilt, in degrees, with the goal being 0°. The particular tilt we are
referring to here is the rotation of the CCD in the focal plane about the optical axis so that
it is no longer perpendicular to the direction of travel of the carriage/target. Tilt can be
corrected for by either adjusting the angle of the fixed rail of the ball-slide or, the CCD
itself. The CCD adjustment is typically only done on the factory’s CCD alignment fixture.
Field adjustments are discouraged because they can tend to corrupt the x and y alignment
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