Polaroid SprintScan SS35, Repair Manual

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Slide Scanner Repair Manual Diagnostics and Troubleshooting
131
Motion and Color Registration Test
Motion/Color registration is a single test which checks for 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.
Note: A stand-alone version of this test can be run to provide graphical feedback and
additional information. Sources of possible problems highlighted by the test results
are:
• Dirty leadscrew
• Other leadscrew or guide rail imperfections such as burrs
• Worn leadscrew nut
• Excessive CCD tilt relative to the angle of the ball slide
• Worn carriage ball slide
• Bad stepper motor
• Leadscrew wobble
Typically, a slide scanner which fails color registration, fails because the Peak Red to Blue
(R-B) Misalignment exceeds the test specifications. 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 without replacing the entire
carriage assembly.
Test Details
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. 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 Red to Blue Misalignment,
the operator can adjust the horizontal magnification to match the vertical magnification,
using the Magnification and Focus target and an adjustment procedure (See MAG and
Focus Adjustments). 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.
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°. In this case, tilt 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. Very small tilt adjustments can
sometimes be made by loosening the mounting screws and rotating the fixed rail of the