5 : T h e o r y o f O p e r a t i o n
CHRISTIE INC. -
CHRISTIE INC. - 35/70 Service/PM Manual
July, 1997
Lead
Network
REGISTRATION MODE
ANALOG
TACH
U2
0 deg sensor
180 deg sensor
E
T
M
13
Pulldown
Drive
D-AMP
U1
M
T
E
U1
PULLDOWN MODE
2275
Drive
Pulldown
D-AMP
37
U55
TACH
PULL
AMP
Pulldown Encoder
Shutter Index
U20
PIA
DAC
U10
VF
Open
Pulldown Amplifier Card
Main Electronics Card
Pulldown Sensor
VF
U21
Pulldown Amplifier Card
Main Electronics Card
12
2275
Figure 5.6: Cine Operation - Pulldown Circuit
The operation of the pulldown circuit during cine motion is shown in Figure 5.6. During registration mode, the Pulldown
motor is used to maintain stationary registration by connecting the differential output of the zero and 180 degree sensors,
each partially blocked by the edge of a disk slot, to the motor through amplifiers U21 and U1. Any motion of the disk
edge across the face of the sensors creates a restoring signal to the motor. During pulldown operation, the CPU maintains
direct control of the Pulldown motor. PIA U10 provides an eight-bit control signal to DAC U20. The analog control
voltage is amplified by U55, U21 and U1 on the Pulldown Amplifier Card, driving the Pulldown motor.
Figure 5.7 shows the timing relationships during the pulldown action. Prior to time 0 on the diagram, the film is in
registration and is being illuminated by the shutter. At time 0 a shutter index pulse signals the CPU to initiate a pulldown.
The CPU opens the TACH AND ANALOG switch U27 and closes the PULL switch U47. A signal is sent through the
PIA and DAC to command the pulldown motor to full speed. The CPU monitors the signal from the pulldown disk
sensor, which has been squared up by comparator U2 on the sensor board. When the fourth slot on the five slots-per-
frame sensor is in the sensor area, which is to say the seventh edge has passed the sensor, the CPU initiates a positive
voltage to the motor to achieve the desired braking. As the motor comes to a stop, the shutter tachometer signal is
summed into U1 on the pulldown amplifier board by closing the TACH analog switch portion of U27. This provides
damping. The circuit is placed into registration mode and the trailing edge of the fifth slot is used to resume registration
for the next frame of the film. An automatic circuit detects any incorrect registration, such as might be caused by a change
in motor characteristics. If registration is not correct, the correction voltage used on the next pulldown is changed to
ensure correct registration.
