Christie 35/70 Maintenance And Service Manual page 67

I n t e r l o c k O p e r a t i o n
The 35/70 Projector has the capability to be directly controlled by an external input in a manner quite different from the
normal Show Controller interface. This feature, called interlock, is normally used when the 35/70 projector is operated in
a Master/Slave configuration or is being driven by an external bi-phase source.
As noted above, the motion of film in the projector is directly controlled in both cine and slew modes by speed control
pulses commanded by the CPU and generated from the DRM. These pulses control the shutter speed, as shown in Figure
5.2, and the Constant Velocity Motor, as shown in Figure 5.3. In each case, signals are sent to U33, the Tacho circuit, to
generate a speed control voltage, and to an up/down counter to provide precise positional control. Pulldown in cine mode
is synchronized by the shutter index pulses, and in slew mode the pulldown motor follows the Constant Velocity Motor.
The torque arms operate the reel motors with the help of the CV Tach. To operate in interlock mode, the signals
generated by the CPU to the constant velocity circuit are replaced by pulses sent from an external biphase source, which is
referenced to the line frequency or some other reference source which is common to all the machines being controlled.
Interlock operation is selected by giving the CPU the appropriate command. Interlock signals are input at connector J11
on the Main Electronics Card.
E O F a n d B O F D e t e c t i o n
The beginning-of-show (BOF) and end-of-show (EOF) signals are input into the main electronic card on connector J6.
The circuitry is shown in the diagram of Figure 5.12. (See also Section 8.14.) The EOF tape is detected by comparator
U35A. The output of U35A goes high while the tape is being detected; it is input to the CPU through a PIA. The BOF
tape is processed in a similar manner by U35B. When a projector is operated in the Slave mode, the detection of EOF
signals is disabled.
P W M S a w t o o t h R a m p
The sawtooth ramp used to generate the PWM signals for motor controllers is generated by two sections of U34 and two
of U36. The sawtooth is generated on capacitor C22, controlled by the charge and discharge rates of Q5 and Q6. The
frequency is about 20 KHz.
F a u l t I n d i c a t i o n s
Indications of operating faults are input to the main electronics card in connector J5. Upper and lower film buckle
switches are monitored by the CPU and also combined in EPLD U29 to provide a ready signal to send to motor control
cards. This ensures the film comes to a smooth stop in the event of a problem, eliminating film breakage and sprocket
hole damage.
The Pulldown Sensor Circuit (2268)
Signals from the zero-degree sensor and the 180-degree sensor of the disk sensor card feed into a differential amplifier,
U1. (See the appropriate circuit diagram in Section 8.9.) The output of U1 is Pin 1 (at R6). The signal there is as shown
in the second trace of Figure 5.7.
As the slotted disk on the pulldown shaft turns, the slots pass in front of the 180-degree sensor, causing amplifier U1B to
move positive. Simultaneously, another web passes in front of the zero-degree sensor and causes U1A to go negative, in
turn causing U1B to go more positive. The resulting pulses, as the disk continues to turn, are counted by the CPU.
Comparator U2 squares up the signal and sends it to the computer over parallel bus PIA2-PB4. When four positive and
three negative transitions have been counted, braking is applied to the pulldown motor. As the amplifier comes down
CHRISTIE INC. - 35/70 Service/PM Manual CHRISTIE INC. -
July, 1997
U35A
5
6
AMP
EOF
Figure 5.12: EOF and BOF Detection Circuits
5 : T h e o r y o f O p e r a t i o n
U35B
7
8
AMP
BOF