(10) Remove diodes and heatsinks from slip
NOTE
ring end frame as necessary after testing as described in
Assure that lead clips are properly
f below.
crimped and soldered to clip, and
(11) Reassemble in reverse order.
that clip is soldered to diode lead.
d. Cleaning, Inspection, Test, and Repair.
CAUTION
Use 60 percent tin 40 percent lead
(1) Wipe brushes and windings with a clean
solder, or other solder with a melting
dry cloth, only. Clean all other parts with any process
point above 360 F. Do not hold
required to thoroughly clean but not damage the part.
soldering iron on leads longer than
(2) Inspect and test rotor and stator windings
necessary.
for continuity or shorted circuits. Inspect bearings for
corrosion, roughness, or wear. Inspect brushes for wear,
(5) Test all diodes after connections have
oil-soaked condition, or weak springs. Inspect slip rings
been completed, as described in f below.
for wear, grooving, or burned spots. Inspect diodes for
burned or damaged condition. Test diodes with an
f. Testing the Diodes. The diodes may be tested
ohmmeter for short or open circuits as described in f
with an ohmmeter that has a 1 1/2 volt cell and a scale
below.
with a 300 ohm value at midrange, or a low voltage (not
(3) Repair or replace defective rotor or
to exceed 12 volt) battery operated test lamp. Test as
windings. Replace worn, corroded, or rough bearings.
follows:
Replace oil-soaked brushes, or those worn to 7/16 inch
long. Replace brush springs that do not have a 10 ounce
(1) Prior to making diode tests, check for a
tension. Replace defective diodes.
short circuit between the heatsink and end frame.
Connect a low voltage test lamp between heatsink and
e. Diode Replacement.
end frame, then reverse the leads. The lamp should light
with leads in one position, but not in the other. If test
(1) Replacement diodes come with uniformity
lamp lights in both directions, the heatsink is shorted to
long leads in order that all positions can be served. If the
end frame, or both diodes of a pair are shorted. If either
diode is to be installed in the heatsink, overall length of
situation exists, it is impossible to locate the defective
diode and lead is to be 1%/s inch. Cut to length by
diode because all will test defective. Visually inspect
holding lead with common pliers and cutting with
heatsink insulators. A shorted heatsink will be burned
diagonals. Do not grip the diode case, or it might receive
around the insulators. When all diodes test defective, clip
internal damage.
all flexible leads then test each diode as described below
(2) When a diode is to be installed in the end
to isolate defective diodes.
frame, first remove old diode by clipping flexible leads on
both sides of diode lead. Clip leads as close as possible,
CAUTION
then unscrew diode from frame.
Do not use 110 volt test lamps to
make these tests.
NOTE
To facilitate diode removal, heat
(2) Remove slip ring end frame (c above).
outside frame to 150 F. in an oven,
(3) Test heatsink ((1) above).
or immerse the frame briefly in water
(4) Connect one ohmmeter lead to a pair of
heated to a temperature just below
diode leads. Connect other ohmmeter lead to one of the
the boiling point.
diode cases of that pair of leads and observe ohmmeter
reading. Reverse the test probes and observe this
(3) With new diode and frame at room
reading. A good diode will have one high reading (above
temperature, coat threads with light engine oil, or silicone
300 ohms) and one low reading (below 300 ohms). Two
grease, then install and tighten to torque of between 160-
high readings, or two low readings indicates diode is
190 inch pounds.
defective.
(4) To replace diodes in heatsink, the
NOTE
heatsink must be removed from end frame, then remove
If a test lamp is used to make diode
and install diodes in a similar manner to that described in
test, the light should glow only once
(1) through (3) above.
when leads are reversed. If the lamp
does not light, or lights in both
directions, the diode is defective.
AGO 20051A
3-4
