Repair manual

2-51
THEORY OF OPERATION
camera back shutter to open allowing the video image that is
displayed on the CRT to expose the film.
Once the exposure sequence is completed, the CADVANCE signal
is removed causing the camera back shutter to close. Closing
the camera back shutter causes the internal mechanism of the
camera back to:
o Eject the exposured film frame for a non-motorized camera
back (Pack Film and 4 x 5). The user must manually remove
the ejected film frame.
o Advances the exposed film frame for a motorized camera back
(35mm and Auto Film). The drive motor internal to the
camera back starts. The motor drives the exposed film frame
onto the wind-up reel and the next unexposed film frame is
positioned directly behind the shutter. It stops automatically.
b. Filter Wheel Motor Control
The Filter Wheel Motor Control circuit (Figure 2-9, sheet 5) initially
rotates the filter wheel assembly to its start (no filter) position. During an
exposure sequence, this control circuit places the specified colored filter
(red, green, or blue) between the monitor display screen and the selected
camera. It accomplishes this action by rotating the filter wheel assembly
until the specified colored is properly positioned.
1) Initial Operation
When the Digital Palette is initially turned on, the initialization
program internal to the Digital Palette EPROM causes the
stepper motor to rotate the filter wheel assembly to its start (no
filter) position.
Upon command, the initialization instructions from the EPROM
are applied to the input of the microprocessor network via the
Address/Data communications bus. The microprocessor network
decodes these initialization instructions from the EPROM and then
applies the filter wheel position output data via the Address/Data
communications bus to the octal addressable latch in the stepper
motor drive network.