IBM Selectric I/O Manual Of Instruction page 26

.----- MOUNT' NG SCREWS
MOUNTING
BRACKET
CONTACT
TRANSMITTING
CONTACTS
FIGURE 51. Print Selection Contact Assembly
Contact Actuatol
A contact actuator will be operated by the selector-latches
that remain under the selector-latch bai I during a selection.
The extension of the latch that is being carried down by the
latch bai I stri kes the contact actuator. The actuator wi II be
pushed down in its guide. The bottom of the actuator has two
cross bars that operate the contacts (Fig. 52). When the selec-
tor-latch bail restores, the contact actuators rise under the
spring tension of the contacts.
The five unit actuator is operated when the five unit latch is
not pulled forward. Operating the -5 unit latch allows the
five unit bai I to rise. The contact actuator rises under the
tension of the contacts (Fig. 52).
Code Check (Parity Check)
The purpose of code check is to determine if the correct num-
ber of selector latches are active during a print selection cycle.
Code checking requires the addition of another selector bail,
selector latch, latch pusher and magnet (Fig. 53). The selec-
tor latch has no mechanical function, other than to operate a
contact. When in the out-put mode the code check magnet is
used to trip the cycle clutch when a plus 5 rotate, 3 tilt char-
acter is selected.
In a machine where more than one selector latch must be active
(pulled down by the bail), if a failure occurs, an unwanted
latch may be pulled down, or a desired latch may pop out from
under the bail. By always transferring an odd number of con-
tacts, failures of this type can be recognized immediately.
FIGURE 52. Contact Actuators
19