IBM Selectric Manual

II Til "0"
+5 +4 +3 +2 +1
o
-1
-2 -3 -4 -5
~ A ~ ~ ~
/' / \ / \ I}. / L~
\ \. / 1\ / L~ / \
/ "/ I [~/ L. ""'\ / \ / \
/ L.. ~v' V V "
/\, /" A /\
/ \ / \ /,
/ \ / \ / } / "
I )\ / 1\ / L \ / L. ~
L.y L~ ~ \
"T"-{+5/-5)
1\
FIGURE 58. Excessive Negative Balance
maladjusted balance lever causes the rotate bellcrank to
receive an excessive amount of motion as illustrated by
the detenting of the negative five rotate position. This
excessive motion is felt equally in all of the negative
selections because the negative end of the balance lever
receives the same motion from the cam for all negative
selections. The progressive loss of motion felt from the
negative five to the negative one rotate position is caused
by the positive side of the balance lever. It produces a
deficiencyofmotion in the negative selections just as it
did during
the positive selections.
Notice the detenting of a negative one selection in Fig-
ure 58. This selection combines the error of a positive
four and a
negative five causing the negative one ("0")
to be the worst detenting selection with respect to the
zero rotate se lection. Although the cance Ilation method
(+5/-5) combines even a greater error than the negative
one selection, either one may be used to effectively make
the balance lever adjustment. Checking the detenting
of the other positions is not necessary.
:fthe balance leverwereoutofadjustment in the opposite
direction so that there was too much positive and not
enough negative motion, the error pattern would remain
the same except that the detents would move towards the
opposite side of the detent notches.
10. Rotate Arm Motion - The adjustable plate on the bottom
ofthe rotate arm (Fig. 59) should be adjusted up or down
sothat a half-cycled upper case letter "W" (+5) detents
the same as a half-cycled upper case letter "R~' (-3).
When observing the detenting remove the head play light-
ly in the negative direction.
The rotate arm motion ismeasuredonlyas far as the nega-
tive three position in the negative direction. The nega-
tive four and five positions are not used because these
two positions are affected by the ratio change operation
of the wear compensator.
Bycomparingthedetentingofthe "R" (-3) and "W" (+5),
it can be determined whether or not the rotate arm is
multiplying the motion, received from the rotate link,
enough to rotate the typehead to the selected position.
Once the "R" and "W" are detenting the same, then all
ofthe selections between positive five and negative three
will detent well within the acceptable band width pro-
vided that all of the previou:. adjustments have been
made correctly. If a slight difference in detenting must
21
exist between the "R" and "W" it is permissible and some-
times desirable provided that the "R" detents more nega-
tive than the "W". In other words, it is better to have
too much rotate arm motion than too little. The reason
forthis is to place a small amount of wear potential into
the system for the areas of the differential mechanism
where
wear cannot be compensated for (positive latches
and latch bail). Thus, as wear occurs in these areas
causi ng the rotate arm motion to decrease, the detenti ng
variation between the "W II and II R" wi II also reduce.
FIGURE 59. Rotate Arm Movement
Fi gure 60 ill ustrates the effects on detenti ng caused by
insufficient rotate arm motion. Notice that the largest
detenting variation occurs between the "W" and "R".
This is because the "W" and "R" operate in opposite
directions and the error that appears when these two
positions
are compared is the co:nbined error of both pesi-
tive and negative ,Y;o[;vn.
If the rotate arm motion was excessive the detenting pat-
tern would remain the same except that each detent would
be on
the opposite side of its detent notc,h.
NOTE: The adjustment may be left loose during each
check unti I the correct position is obtained.

IBM Selectric Specifications

General

Type	Electric typewriter
Introduced	1961
Keyboard Layout	QWERTY
Carriage Return	Electric
Manufacturer	IBM
Printing Technology	Typeball (golf ball)
Power Source	AC Power
Power Supply	120V AC