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
4 Pulldown
Motor
Voltage (20.00 v)
3 90-degree
Sensor (5.00 v)
2 Pulldown
Signal (TP13)
(5.00 v)
1 Pulldown
Tachometer
(5.00 v)
Pulldown
Figure 5.7: Pulldown Circuit Timing for 60FPS
The pulldown circuit also performs the Automatic Loopset function. Under CPU control, the pulldown sprocket is turned
slowly until the film speed drops below a set value. The CPU rewinds four and one-half frames and stops in registration.
A two-second timeout stops the pulldown motor if there is no film in the projector and illuminates LED <3> on the
keypad.
A framing switch has been incorporated to aid the operator in proper framing. The five positions of the framing switch
allow the relationship between the encoder slot selected for registration and the indexing slot to be changed in increments
of 1 film perforation, for 70mm film. For 35mm film the increments equal 1/5 of the 4 perforation film frame. This avoids
the need to relocate the film on the sprocket if the film is not framed.
