TM 5-3810-206-35
long leads in order that all positions can be served. If
(4) Connect one ohmmeter lead to a pair of
the diode is to be installed in the heatsink, overall length
diode leads. Connect other ohmmeter lead to one of the
of diode and lead is to be 1 3/8 inch. Cut to length by
diode cases of that pair of leads and observe ohmmeter
holding lead with common pliers and cutting with
reading. Reverse the test probes and observe this
diagonals. Do not grip the diode case, or it might
reading. A good diode will have one high reading
receive internal damage.
(above 300 ohms) and one low reading (below 300
(2) When a diode is to be installed in the end
ohms). Two high readings, or two low readings indicate
frame, first remove old diode by clipping flexible leads on
diode is defective.
both sides of diode lead. Clip leads as close as
Note. If a test lamp is used to make
possible, then unscrew diode from frame.
diode test, the light should glow only
Note. To facilitate diode removal,
once when leads are reversed. If the
lamp does not light, or lights in both
heat outside frame to 150 F. in an
directions, the diode is defective.
oven, or immerse the frame briefly in
(5) Test the second diode of the pair in a similar
water heated to a temperature just
manner.
below the boiling point.
(6) Proceed to remaining pairs of diodes and
(3) With new diode and frame at room
test in similar manner described in (4) and (5) above.
temperature, coat threads with light engine oil, or
(7) Replace defective diodes (e above).
silicone grease, then install and tighten to torque of
g. Testing the Stator.
between 160-190 inch pounds.
(1) Remove stator from slip ring end frame (
c
(4) To replace diodes in heatsink, the heatsink
above).
must be removed from end frame, then remove and
(2) Connect one ohmmeter test probe to any of
install diodes in a similar manner to that described in (1)
the three stator leads, then touch stator frame with
through (3) above.
remaining test probe. Observe ohmmeter reading. This
Note.
Assure that lead clips are
reading should be very high (full scale). A low reading
properly crimped and soldered to
indicates a grounded stator winding. Replace the stator
clip, and that clip is soldered to diode
when a low reading is observed.
lead.
(3) Touch the test probles to any of two of the
stator leads.
Zero resistance should be read on
Caution: Use 60 percent tin 40
ohmmeter.
When high resistance is read, stator
percent lead solder, or other solder
windings are open, and stator must be replaced.
with a melting point above 360 F. Do
Note. A test lamp should light when
not hold soldering iron on leads
connected between the two slip
longer than necessary.
rings.
(5) Test all diodes after connections have been
h. Rotor Test.
completed, as described in f below.
(1) Remove slip ring end frame (c above).
f. Testing the Diodes. The diodes may be tested
(2) Connect ohmmeter leads between either slip
with an ohmmeter that has a 11/2 volt cell and a scale
ring and rotor shaft. Observe reading. Reading should
with a 300 ohm valve at mid-range, or a low voltage (not
be very high (full scale). If a low reading is obtained, the
to exceed 12 volt) battery operated test lamp. Test as
windings are grounded and should be replaced.
follows:
Note. A test lamp should not light
(1) Prior to making diode tests, check for a short
when connected between one slip
circuit between the heatsink and end frame. Connect a
ring and the shaft
low voltage test lamp between heatsink and end frame,
(3) Connect one ohmmeter lead to each slip
then reverse the leads. The lamp should light with leads
ring. Low resistance should be indicated (approximately
in one position, but not in the other. If test lamp lights in
two ohm). If a high reading is obtained, the windings are
both directions, the heatsink is shorted to end frame, or
open and should be replaced.
both diodes of a pair are shorted. If either situation
Note. A test lamp should light when
exists, it is impossible to locate the defective diode
connected between the two slip
because all will test defective. Visually inspect heatsink
rings.
insulators. A shorted heatsink will be burned around the
(4) Windings can be checked for short-circuits
insulators. When all diodes test defective, clip all flexible
by connecting a battery and ammeter in series with the
leads then test each diode as described below to isolate
two slip rings. Note the ammeter reading. It should read
defective diodes.
between 3.6 and 4.0 amperes. When high amperage is
Caution: Do not use 110 volt test
indicated, windings are shorted and should be replaced.
lamps to make these tests.
(2) Remove slip ring end frame (c above).
(3) Test heatsink ((1) above).
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