Fourth Inspection Period - IBM Selectric Maintenance Manual

FOURTH INSPECTION PERIOD
ESCAPEMENT
1. The carrier should escape smoothly and positively through-
out the full length of the writing I ine and through the right-
hand margin under letter escapement, spacebar operation,
and tabulation.
2. Check for frayed or loose transport cords.
3. Tension should be maintained on the right-hand transport
pulley to maintain its mounting parallel to the power
frame. Its outside flanges should be 1-7/32" from the
right-hand outside surface of the power frame.
4.
The line-gage holder must clear the platen at all points,
and not impede carrier motion.
5. A minimum of .010" clearance should exist between the
carrier-return shoe and the spring-clutch. Note, however,
that excessive clearance can result in erratic carrier-
return motion.
6. Check for 1/2-3/4 pounds of mainspring tensiqn measured
at the carrier as it escapes through the linelock load at
the extreme right-hand margin.
7. Check for .002" - .004" backlash of the tab gOVElrnor and
carrier-return pinion gears with the escapement gear;
8. Letter escapement should occur as soon after print as pos-
sible.
9.
The trigger guide should disengage the trigger from the
escapement-torque-bar arm when the escapement pawl
has cleared the rack by .010" - .015". Both the letter-
escapement and the spacebar operation should allow
.005" - .010" excess motion after the trigger has dis-
engaged the trigger from the torque-bar arm.
10. When operated, the tab lever should overthrow the tab-
lever latch by .005" - .010" without being choked off
by the tab torque-bar lockout lug or backup eccentric,
and without overthrowing into the tab rack. Observe the
operation at both ends and the middle of the torque bar.
Dynamically check for tab failures using five irregularly
set tab stops for at least five columns.
11. Check to make sure that the carrier-return operation un-
latches the tab when both operations occur simultaneous-
ly.
12. With the backspace operated manually, the escapement
pawl should just fail to get a new tooth on the escape-
ment rack.
13. There should be a clearance of .005" - .015" between
the front of the backspace pawl and a tooth of the back-
space rack (with the carrier at rest).
14. Overthrow clearance of .010" - .020" is required be-
tween the interposer pawls and the operational-latch
bracket wh'en the operational cams are on their high
point.
MOTOR DRIVE AND CARRIER RETURN
1. Check for adequate tension of the motor-pulley belt, or
for a frayed or noisy belt.
2.
The selector and operational cam shafts, and the print
and filter shafts, must have .002" end play.
3.
There must be freedom from binds in the idler gear train
with minimum backlash.
4.
With the carrier-return cam on its high point, the carrier-
return arm should overthrow its keeper by .020" - . 030" .
5.
The carrier-return brake shoe should cause the carrier-
return spring clutch to drive the carrier no later than
when the escapement pawl clears the last one-third of
the escapement rack tooth. The clutch shoe should
overlap the last three coils of the spring clutch.
6.
The carrier-return unlatching link must positively un-
latch the carrier-return latch at the left-hand margin
with .005" - .010" overtravel when the margin-rack
overbank is set.
7. The escapement pawl must not drag the escapement rack
during carrier-return operations.
8. Measure one-half to one pound tension of the shock un-
loader at the left-hand margin while unlatching the
carrier-return keeper-latch arm.
INDEXING AND PAPER FEED
1. Check for. 015" - .030" clearance between the platen
ratchet and the index pawl, at rest.
2. Index operation should result in one full-tooth motion of
the index pawl with respect to the platen ratchet (in
single-linespace position) and two full-teeth motion
with no evidence of hesitation or drag (in the double-
I inespace position).
SHIFT
Check the cam and spring for rust. Turn power on, and hold
the shift ratchet (grey section). Release the ratchet by press-
ing the magnet. Allow the ratchet to rotate slowly while
holding down on the magnet. The shift cam should stop at a
fully detented position for each 180
0
operation. The white
nylon roller should seat fully in cam notch.
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