Section 6: ELECTRICAL
PA1553
42
NOTE
When replacing a diode, make sure it is
designed for a negative ground system. The
diode can be identified by the symbol stamped
on the diode case. The arrow must point
toward the diode flexible lead.
To replace the three diodes that are mounted in
the supports attached to the stator lead studs, it
is necessary to remove the diode and support
assembly. The two outer diode and support
assemblies are identical and can be installed on
either side. The center unit has a different
support, with 2 inches (50,8 mm) between the
mounting hole centers.
NOTE
The outer supports are provided with 2 ¼"
(57,15 mm) center holes.
7.3.1 Diode Replacement (in Support)
1. Remove nut with lock washer attaching the
diode support to the stator lead stud.
2. Remove nut, lock washer, and flat washer
attaching support to the small stud in the
end frame.
3. Remove the diode and support assembly.
Then remove insert from small hole in
support or from small stud in the end frame.
4. Remove nut and flat washer from diode
mounting stud, and then remove diode from
the support.
5. Place a new diode in the support and install
a flat washer and nut on the diode mounting
stud. Hold the diode with a wrench placed
over flats on the diode, while tightening nut
on the mounting stud to a torque of
160-180 lbf-in (18-20 Nm).
6. Place diode and support assembly over the
stator lead stud and the small mounting
stud. Place insert over small stud inside the
hole in the support. Install flat washer, lock
washer, and nut on the small stud, and
tighten to a torque of 22-25 lbf-in (2-3 Nm).
Install nut with lock washer on stator lead
stud and tighten firmly.
7.3.2 Diode Replacement (in End Frame)
To remove diode, use a thin 1 inch open end
wrench on flats of the diode case to unscrew
diode from the end frame. Thread the new diode
into the end frame and tighten to a torque of
160-180 lbf-in (18-20 Nm). If no other parts are
to be replaced, refer to “DIODE END COVER
INSTALLATION” in this section.
7.4 FIELD REMOVAL
1. Remove three diode and support
assemblies from the end frame to provide
access to the lower field to end frame bolts
(2).
2. Remove nut with lock washer and flat
washer from three stator lead studs.
3. Remove the six bolts and lock washers
attaching the diode end frame to the stator
frame.
4. Separate the end frame from the stator
frame, and remove the end frame and field
assembly from the rotor while pushing the
stator lead studs out of the end frame.
5. Remove nut, lock washer, flat washer, and
insulating washer which secure the field
lead terminal stud in the end frame. Push
the stud out of the end frame.
6. Remove field terminal stud insulating
bushing and seal from the end frame.
Remove insulating sleeve from the field
terminal stud.
7. Remove the four bolts and lock washers
attaching the field to the end frame.
8. To separate the field from the end frame,
install four 3/8-24 x 3 inch bolts in place of
the 3/8-24 x 2 inch bolts removed in step 7.
Thread bolts in to even heights. Support the
end frame in an arbor press. Then, using a
suitable press plate to exert pressure on all
four bolt heads, press the field out of the
end frame.
7.5 FIELD INSTALLATION
1. Position the field assembly on the end
frame. Insert four 3/8-24 x 3 inch bolts
through the end frame and thread into the
field to keep holes aligned.
2. Support the end frame on an arbor press
bed so that the diodes will not be damaged,
and press the field into the end frame. Press
in until shoulder on field coil bottoms against
the end frame.
3. Remove the four guide bolts. Install four 3/8-
24 x 2 inch bolts, using new lock washers to
attach the field to the end frame. Tighten
bolts securely.
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