Polaroid Land SX-70 User Manual page 20

c- Switch S3, normally closed at the begining
of the exposure cycle is opened by the recock
ram located in the gear train assembly. See
Figure 2-7. As the exposure sequence begins,
S3 opens and actuates a delay circuit (Y delay)
in the EMC which retards the start of the actual
exposure approximately 40 milliseconds so
that mirror bounce will have subsided before a
picture is taken. At the end of the delay time, the
shutter starts to open and the electronic timing
function (integration) takes place. If a flash circuit
is inserted into the FFA (S2 closed) an additional
flash delay circuit is avtivated to insure that the
exposure gets full effect of the light derived from
the flash. At the end of the exposure cycle when
the Fresnel carrier moves down into viewing
position, S3 closes as the recock ram moves
away. It is now reset for the next camera cycle.
d- Switch S4 is tripped by an actuator on the
plunger of solenoid #1, the shutter blade actuating
solenoid (Figure 2-8).
Figure 2-7 S3 Being opened by recock ram
NOTE : Whenever the SX-70 shutter is discussed,
it must be noted that, since the camera is a single
lens reflex and focusing is accomplished through
the taking lens, the shutter's normal state si open,
not closed as in other Polaroid cameras.
When the shutter release button is pressed and
the exposure cycle is initiated full battery power
is delivred to solenoid #1, closing the shutter.
Once the solenoid plunger is seated it no longer
requires as much power as was originally
needed to overcome its static inertia. Switch S4,
therefore, closes the S4 CB contacts to the ECM
and the electrical power to the solenoid coil is
reduced to the «power down» value which is
sufficient to continue the exposure cycle yet low
enough to conserve battery drain.
When the switch S4 (CB contacts closed) transfers
to the ECM it sends power to the drive motor and
operates the gear train. When S4 is actuated,
(CB contacts closed) it also disconnects power
from the FFA flash circuitry. This action prevents