Centronics 101AL Technical Manual page 80

DRIVING MECHANISM
B. Clutch Alinement and Function (Fig. 8-3A)
Alinement of clutches is as follows: Viewed from the front of
the printer (right side), the order is - reverse clutch assembly
(HB-139) followed by forward clutch assembly (HB-139). Because
of a preload condition (surface to surface contact) between
splined armature (HB-142) and keyed rotor (HB-141) no gap ad-
justment is required. Slight tension (preload) is maintained
by a spring (HB-144) pressing against the fixed, forward and
reverse driving pulley (HB-60) and its splined armature (HB-142).
The armature hub (HB-143) inserts into the splined armature
maintaining torque drive for either forward or reverse drive.
Clutch field assembly (HB-140) is prevented from rotating about
its shaft (HB-50) by means of tabs (See Fig. 8-3A, A and B) that
extend from field assemblies (HB-140) and mount to the printer
base. When a signal is sent from electronic logic to coil in
forward or reverse clutch field assembly, the magnetized rotor
(HB-141) holds the splined armature (HB-142), and friction torque
is transmitted to shaft and drive pulley (HB-60) (forward or
reverse). When signal current stops, torque chain between armature
and rotor is discontinued, and the armature is restored to initial
preload condition (surface to surface contact).
C. Operating Conditions, Drive Mechanism (Figure 5-2)
Alternate forces are exerted on timing belts (HB-48, and belt 49)
including main drive belt (HA-36) and motor (HB-98) because of
inertia of print head carriage and forward and reverse clutch
timing peaks. These variations in the power transmission route
are normally handled by the use of a motor clutch plate (HB-98)
(part of motor) and motor pulley driver (HB-92) installed to
protect belts and motor.
Normal cycle time of carriage and machine operating sounds are
directly influenced by alternate dropping and raising time of
torque on clutches, which also affect belt tensions. Therefore,
all drive mechanism parts should be properly adjusting using
recommended procedures where applicable.
5.2.3.2 Removal/Replacement Procedure
A. Main Motor (HB-98) (With covers and rear electronic cavity removed)
(Retain all mounting hardware and parts if replacing motor)
Steps A.1. through A.5. are keyed to Figure HI.
1. Remove right and left-hand bevel gears (HI-27) by loosening
set-screws (HI-29).
2. Remove right and left-hand shaft bushing holders (HI-130, 133)
by removing screws (HI-131).
5-8