TM 5-6675-316-14
(5) When the current in the coil is turned off, the collapsing field will
induce transients. These are shunted back into the -26 V supply by diode CR4, zener
diode CR14 and Darlington Q12. Each motor coil is driven with the same basic
circuit so the program provides four signals in sequence to drive the stepping
motor, and the film is advanced the requisite number of steps upward at the
completion of each line of type.
c. Variator or enlarging lens drive system. The variator or enlarging lens
moves backward and forward on a carriage driven by a helix screw and stepping motor.
The main program determines the position of the lens by feeding information on the
requisite number of motor steps.
2-22
