IBM Selectric Maintenance Manual page 49

not occurring at the negative four position, thus the arm
assembly is operating as one soli d arm at this position.
In Figure 85C the correct amount of rati
0
change is in
the system. All positions from the -3 to the +5 detent
the same as the -5. Note that when the -3 detents the
same as the -5, the detenting of the -4 is slightly dif-
ferent. This is caused by the ratio change. No attempt
should be made to control the detenting of the -4 posi-
tion because its position may vary on each machine de-
pending on the amount of ratio change required (of each
machine) to make the -3 detent the same as the -5.
13. Print.Shaft Timing (Final) - Advance or retard the print
shaft relative to its gear to obtain the proper timing of
the rotate detent. Hand-cycle an upper case -5 char-
acter and observe the rotate detent as it operates in the
typehead notch. The detent must enter the correct de-
tent notch and withdraw without restricting the restoring
of the typehead. There should be .002" to .004" back-
lash felt in the type head when the detent is near the
bottom of the s lope of the detent notch (Fig. 86).
Typehead Restoring
~
t
FIGURE 86. Withdrawal Clearance
For The -5 Character
After adjusting the timing of the rotate detent to the up-
per case -5 character, check the detent entry and with-
drawa I of an upper case +5 character. If the detent re-
stricts the typehead from restoring on withdrawal when
the +5 is slowly hand-cycled, advance the print shaft
slightly until the +5 has a withdrawal backlash of .002"
to .004". When the withdrawal adjustment has been
completed check the detent entry on both the +5 and -5.
The detent must enter the correct notch.
CAUTION: After hand-cycling the machine the com-
pensator roller must be raised to the top of the wedging
slot and reseated under power by striking a series of
-5 cha racters.
If difficulty is encountered in obtaining the correct de-
tent timing, check the following items:
a. Detent ski rt clearance - favor the high side of the
tolerance.
b. Typehead homing - favor the high side of the tol-
erance.
c. Band width - make sure that it is not excessive.
2-26
d. Head play - it should be .045" measured at the
type head skirt. If excessive head play is suspected
the ball joint should be replaced and the typehead
homing adjustment refined.
CAUTION: Excessively advanced or retarded timing
can cause parts damage as well as poor horizontal align-
ment or improper selection. This could happen if the
detent entered the wrong notch or remai ned in the notch
too long.
NOTE: Be sure to maintain .002" to .004" end play in
the pri nt shaft.
14. Shift Motion - The shift arm adjusting screw (Fig. 87)
should be adjusted in or out to obtain 180
0
rotation of
the typehead during a shift operation.
The adjustment can be checked by observing the detent-
ing in the lower case compared to the upper case using a
-5 character. The detent MUST enter the lower case
notch EXACTLY the same as it does the upper case notch.
Check by half-cycling the machine and manually with-
drawing the detent. Remove the head play clockwise
and allow the detent to re-enter slowly. A final check
~an be made by comparing the detent withdrawal timing
of the upper and lower case. They must be exactly alike •
.1:"'--_
Sh i ft Arm
Adjusting
Screw
...
~
FIGURE 87. Shift Motion Adjustment
Maladjustment can cause misalignment in the lower case
while the upper case remains good.
CAUTION: Be sure that the shift arm is detented at
each position during the check and that the cycle shaft
is properly latched at the half-cycle position.
15. Final Check - After completing the foregoing adjustments,
a final check should be made to see if any refinements
are necessary. Compare the coarse alignment of 0 rotate
compared to +5, -1, -3, -4, -5. The band width of this
group should not exceed .030" and none of the group
should detent closer than .010" to the center of the notch
when the head play is removed in the negative direction.
The following table can be used to diagnose the cause of
excessive band wi dth between a 0 rotate and +5, -1, -3,
-4, -5. These characters are chosen because of thei r
rotate se lecti ons. If an excessive band wi dth exists,
it wi II be greatest among these characters. In making
the diagnosis follow the sequence as listed.