IBM Selectric Maintenance Manual page 45

rotate character, it indicates thot the typehead has
moved because of an unbalanced condition between the
positive and negative motions.
With the machine in the half-cycled position using the
cancellation method, adjust the right hand member of
the balance lever left or right unti I the detenting is ex-
actly as it is when a zero rotate character is half-cycled
normally. Changing the balance lever adjustment will
not appreciably affect the detenting of the half-cycled
zero rotate character (latched home).
NOTE: The nut on the balance lever screw can be left
loose unti I the correct adjustment is obtained. Be sure
not to move the adjustment when tightening the nut.
In (Figure 76) the effects of the wear compensator are dis-.
regarded and all adjustments are correct except the bal-
ance lever. The right hand member of the balance lever
is maladjusted too far to the left creating too much nega-
tive motion and not enough positive motion. Looking at
the positive side of Figure 76 you can see that the mal-
adjusted balance lever causes a progressive loss of motion
to the rotate bellcrank from the zero to a positive five
rotate position. The greatest loss of motion is felt at the
positive five position because the left end of the balance
lever receives the most motion for this selection. When
the negative side of the balance lever is operated, the
ma ladjusted ba lance 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
deficiency of motion in the negative selections just as it
did during the positive selections.
Notice the detenting of a negative one selection in Fig-
ure 76. This selection combines thp. error of a positive
four and a negative five causing the negative one to be
the worst detenting selection with respect to the zero
rotate selection. Although the cancellation 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 de-
tenting of the other positions is not necessary.
+5
+4
+3
+2
+1
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If the balance lever were out af adjustment in the oppo-
site 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.
JO.
Rotate Arm Motion - The adjustable plate on the bottom
of the rotate arm (Fig. 77) shou Id be adj usted up or down
so that a half-cycled upper case +5 rotate character de-
tents the
SQm~
as a half-cycled upper case -3 rotate
character. When observing the detenting remove the
head play lightly in the negative direction.
The rotate arm motion is measured only as far as the neg-
ative three position in the negative direction. The neg-
ative foui' and five positions are not used because these
two positi'ons are affected by the ratio change operation
of the wear compensator.
FIGURE 77. Rotate Arm Movement
By comparing the detenting of the -3 and +5, it can be .
determined whether or not the rotate arm is multiplying
the motion, received from the rotate link, enough to ro-
tate the typehead to the selected position. Once the -3
and +5 characters are detenting the same, then all of the
selections between positive five and negative three will
-1
-2 -3
.-4 -5
1\
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[y
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1\ I L \ /
L.
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-y \
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FIGURE 76. Excessive Negative Balance
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