Polaroid SX70 manual S3 Being opened by recock ram

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).

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.

WhentheswitchS4(CBcontactsclosed)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

Figure 2-7 S3 Being opened by recock ram