Motor Rapid Stop Circuit During Mode Selection - Polaroid Miniportrait 455 Repair Manual

3. As cam (B) turns through the action of the gear train, an arm of the S4 switch (C) drops
into a valley on the cam, opening S4 (turning it OFF).
4. When S4 is driven to an OFF position, gate G of Q8 (Figure 2-6) goes high, activating
Q8 to short the motor input power and bring it to a rapid stop.
SR Switch
Motor
Figure 2-6. Motor rapid stop circuit during mode selection
5. To achieve the correct exposure action, the rotation of the M blade (a) and MS
blade (b) is controlled by pins (d') and (d). These pins are moved up or down by the
cam "steps" on the ends of the mode select lever "A" shown in the circled areas of the
illustration. The pins are thus in or out of the rotational paths of the blades, preventing
or allowing blade rotation (see the three circled areas at right in illustration).
The M and MS blades, therefore, rotate or remain fixed, according to the exposure
mode selected (single-, dual-, or 4-frame. The operation of each of these modes will
now be explained in more detail.
17