3M
Overhead Projector 9800 Series
Section 4 – Adjustments
4-1
9800 Service Manual
3M 1996
4-1.
Setting Up A Test Facility
Reliable check-out and optical alignment of overhead
projectors can be accomplished only if proper testing
facilities are available. The following items,
described in this section, are required to provide
proper testing:
•
Permanent viewing screen
•
Permanent test facility (stand or bench)
•
Required tools
4-1-1. Permanent Viewing Screen
A permanent viewing screen with a flat non-reflective
white surface can be provided by applying a flat white
paint to a 152 cm by 152 cm (60 in. x 60 in.) area of a
smooth wall. If a smooth wall is not available, a
piece of wallboard painted white, or a white window
shade of the proper size, can be mounted in the test
area. A portable screen may also be used.
A test stand or bench should be permanently located
about eight feet from the screen. It should be high
enough to provide easy access to all parts of the
overhead projector when it is placed on the stand for
testing. An electrical outlet and a switch should be
built into the test stand to facilitate making electrical
connections to the projector.
4-1-2. Test Facility Layout
To eliminate vertical and horizontal keystoning, it is
very important to align the projector to be perfectly
square with the viewing screen. Keystoning will
result in unequal focusing of projected images at the
four corners, and will especially affect resolution.
Use the steps below to set up a test facility that will
provide the proper screen to projector relationships.
1. Select a smooth wall with a 152 cm x 152 cm (60
in. x 60 in.) area and place a sturdy bench or test
stand about eight feet away from the wall
(Figure 4-1).
2. Set the overhead projector on the test stand so that
it points towards the wall.
Figure 4-1. Test Facility Layout
3. Measure the vertical distance from the floor to the
center of the front projection lens (Figure 4-2).
a.
Follow a floor or ceiling tile from the
projector to the wall or stretch a string from
the center of the projection lens to the wall
and use a carpenter’s square to find the point
at which the string is perpendicular to the
wall.
b. Mark a spot on the wall that is the same
distance (height) from the floor as the center
of the projection lens.
9800-85I
Figure 4-2. Projector to Screen Alignment
4. Mark the position of the stand legs on the floor
and the position of the projector base on the stand.