Repair manual

2-10
THEORY OF OPERATION
move the filter wheel to its start (0) position. If the next instruction is to a
higher filter position, the filter wheel rotates directly to the specified
position. If the instruction is to a lower filter position, the microprocessor
control circuit directs the filter wheel to first rotate to the start (0) posi
tion and then counts to the requested filter position.
The filter wheel assembly has six notches (or slots) on its rim. The
notches are read by the photo interrupter (position sensor). By this
method, the specified colored filter is properly positioned in front of the
CRT screen before the images are exposed to the film.
c. Filter Wheel Photo Interrupter (Position Sensor)
The filter wheel photo interrupter is a U-shaped electrical device
mounted on the Digital Palette housing. It consists of a light emitting
diode (LED) and a phototransistor.
This device, in conjunction with the microprocessor control circuit on the
Logic Controller P.C. Board, generates the signals which are responsible
for positioning the specified filter (red, green, or blue) between the CRT
display screen and the film.
As the filter wheel assembly rotates to bring the specified colored filter
into position, notches on the rim of the filter wheel assembly pass by the
photo interrupter.
Each time a notch passes by, a pulse is generated and sent to the
microprocessor control circuit on the Logic Controller P.C. Board. This
circuit counts the generated pulses to determine when and if the specified
colored filter is properly positioned.
Once the specified number of pulses are counted, indicating that the
specified filter is in position, the microprocessor control circuit on the
Logic Controller P.C. Board stops the filter wheel
in that position.
d. Filter Wheel Stepper Motor
The filter wheel stepper motor is mounted on the Digital Palette
housing. It provides the required driving power to rotate the filter wheel
assembly. A small rubber roller attached to the stepper motor shaft
transfers this driving power from the stepper motor to the filter wheel
assembly.
Pulses from the microprocessor control circuit on the Logic Controller