are replaced, be sure that positive diodes are
(1) The stator windings may be checked with
installed in heat sink and negative diodes in-
a 110-volt test lamp or an ohmmeter. If the lamp
stalled in end frame.
lights, or if the meter readings is low when
connected from any stator lead to the frame, the
Do not strike any of the diodes while
windings are grounded. If the lamp fails to light,
removing. Shock may cause damage to
or if meter reading is high when successively
the other good diodes.
connected between each pair of stator lead, the
h. Slipring Servicing.
windings are open.
(1) If the springs are dirty, they may be
(2) A short circuit in the stator windings is
cleaned and finished with 400 grain or finer
d i f f i c u l t to locate wit bout laboratory test
polishing cloth. Spin the rotor in a lathe, or
equipment due to the low resistance of the
otherwise spin the rotor, and hold the polishing
windings. However, if all other electrical checks
cloth against the sliprings until they are clean.
are normal and the generator fails to supply rated
output, shorted stator windings are indicated.
The rotor must be rotated in order that
f. Diode Checks. One method of checking
sliprings will be cleaned evenly. Cleaning
diodes is to use an ordinary ohmmeter. The lowest
the sliprings by hand without spinning
range scale on the ohmmeter should be used and
the rotor may result in flat spots on the
the ohmmeter should have a 1 ½ volt cell. To
sliprings, causing brush noise.
determine the cell voltage, turn the selector to the
(2) Sliprings which are rough or out-of-round
lowest scale, and then connect the ohmmeter
should be trued in a lathe to .002 inch maximum
leads to a voltmeter. The voltmeter will indicate
indicator reading. Remove only enough material
the cell volt age,
to make the rings smooth and round. Finish with
(1) With the stator disconnected, check a
400 grain or finer polishing cloth and blow away
diode in the heat sink by connecting one of the
ohmmeter leads to the heat sink, and the other
ohmmeter lead to the diode lead, and note
i. Bearing Replacement and Lubrication,
the reading. Then reverse the ohmmeter lead
(1) The bearing in the drive end frame can be
c o n n e c t i o n s and note the reading. If both
removed by detaching the retainer plate screws
readings are very low, or if both readings are very
and then pressing the bearing from the end frame.
high, the diode is defective. A good diode will give
If the bearing is in satisfactory condition, it may
one low reading and one high reading. Check the
be re-used, and it should be filled one-quarter full
other two diodes in the heat sink in the same
with special grade ball bearing lubricant before
(2) To check a diode mounted in the end
frame, connect one of the ohmmeter leads to the
Do not overfill, as this may cause the
end frame, and the other ohmmeter lead to the
bearing to overheat.
diode lead and note the reading. Then reverse the
(2) To install a new bearing, press in with a
ohmmeter lead connections, and note the reading.
tube or collar that just fits over the outer race. It
If both readings are very low, or if both readings
is recommended that a new retainer plate be
are very high, the diode is defective. A good diode
installed if the felt seal in the retainer plate is
will give one low reading and one high reading.
hardened or excessively worn.
Check the other two diodes in the end frame in the
(3) The bearing in the slipring end frame
s h o u l d be replaced if its grease supply is
g. Diode Replacement.
e x h a u s t e d . No attempt should be made to
(1) Diodes are pressed into the end frame
relubricate and re-use the bearing. To remove the
and heat sink. To remove diodes, use a piece of
bearing from the slipring end frame, press out
tubing slightly larger than the diode to support
with a tube or collar that just fits inside the end
the heat sink or end frame, while pressing out the
frame housing. Press from the outside of the
housing towards the inside.
(2) When pressing in a new diode, use a piece
(4) To install a new bearing, place a flat plate
of thin-wall tubing that will contact only the outer
over the bearing and press in from the outside
rim of the diode, to press the diodes in place.
towards the inside of the frame until the bearing
Support the heat sink and end frame with a larger
is flush with the outside of the end frame. Support
piece of tubing as before.
the inside of the frame with a hollow cylinder to
(3) Positive diodes are marked with red
prevent breakage of the end frame. Use extreme
printing, negative diodes with black, If all diodes