Guardian 4389 Repair Manual page 43

AC GENERATORS
2. Set a VOM to measure resistance.
3. Connect one meter test lead to Pin 9 (Wire 0) of the C2
connector (female side). Connect the other meter test
lead to Pin 10 (Wire 4) of the C2 connector (female
side). Rotor resistance should be measured (see
Specifications in front of book). If rotor resistance is not
measured proceed to Step 4. If rotor resistance is mea-
sured proceed to Step 12.
4. See Figure 6. Carefully inspect brush wires; make sure
they are properly and securely connected.
5. Wire 0 from the negative (-) brush terminal connects to
Pin 9 of the C2 connector.
Test this wire for an open condition. Remove Wire 0
from the brush assembly. Connect one meter test lead
to Wire 0. Connect the other test lead to Pin 9 (Wire 0)
of the C2 connector ( female side). CONTINUITY
should be measured. If INFINITY is measured repair or
replace Wire 0 between the brush assembly and the C2
connector.
6. Wire 4 from the positive (+) brush terminal connects to
Pin 10 of the C2 connector.Test this wire for an open
condition. Remove Wire 4 from the brush assembly.
Connect one meter test lead to Wire 4. Connect the
other meter test lead to Pin 10 (Wire 0) of the C2 con-
nector (female side). CONTINUITY should be mea-
sured. If INFINITY is measured repair or replace Wire 4
between the brush assembly and the C2 connector.
7. Connect one meter test lead to Wire 4 Connect the
other meter test lead to frame ground. INFINITY should
be measured. If CONTINUITY is measured a short to
ground exists on Wire 4 repair or replace Wire 4
between the brush assembly and the C2 connector.
8. If CONTINUITY was measured in Steps 5 and 6 pro-
ceed to Step 9.
9. Disconnect Wire 0 and Wire 4 from the brush assembly.
Remove the brush assembly from the bearing carrier.
Inspect the brushes for excessive wear,damage.
10.Inspect the rotor slip rings. If they appear dull or tar-
nished, they may be polished with a fine sandpaper. DO
NOT USE METALLIC GRIT TO POLISH SLIP RINGS.
11.If brush assembly and slip rings look good proceed to
Test 10 ( Test Rotor Assembly)
12.Wire 0 connects from the C2 connector to the control
panel ground lug. Connect one meter test lead to Pin 9
(Wire 0) of the C2 connector (male side). Connect the
other meter test lead to the ground terminal in the con-
trol panel. CONTINUITY should be measured. If INFINI-
TY is measured repair or replace Wire 0 between the
C2 connector and the ground terminal.
PART 2
13.Remove Wire 4 from the voltage regulator.
14.Connect one meter test lead to Pin 10 (Wire 4) of the C2
connector (male side). Connect the other meter test
lead to Wire 4 removed from the Voltage regulator.
CONTINUITY should be measured. If INFINITY is mea-
sured repair or replace Wire 4 between the C2 connec-
tor and the voltage regulator.
RESULTS:
1. Repair, replace or reconnect wires as necessary.
2. Replace any damaged slip rings or brush holder.
3. Clean and polish slip rings as required.
TEST 10 - TEST ROTOR ASSEMBLY
DISCUSSION:
A rotor having completely open windings will cause
loss of excitation current flow and, as a result, gener-
ator AC output voltage will drop to "residual" voltage.
A "shorted" rotor winding can result in a low voltage
condition.
PROCEDURE:
I. Disconnect the brush wires or remove the brush holder,
to prevent interaction.
2. Set a VOM to its "R x 1" scale and zero the meter.
3. Connect the positive (+) VOM test lead to the positive
(+) rotor slip ring (nearest the rotor bearing); and the
common (-) test lead to the negative (-) slip ring. The
meter should read approximately 10-20 ohms. Compare
to "Specifications," in the front of this manual.
4. Now, set the VOM to a high resistance scale (such as "R
x 10,000" or "R x 1K"). Again, zero the meter.
5. Connect the positive (+) VOM test lead to the positive
(+) slip ring and the common (-) test lead to a clean
frame ground. The meter should indicate INFINITY.
RESULTS:
1. Replace rotor assembly if it is open or shorted.
2. If rotor tests good, perform "Insulation Resistance Test"
in Section 1.4.
NOTE: Be sure to read Section 1.4, "Testing, Cleaning
and Drying", carefully. If the rotor tests good, try per-
forming an insulation resistance test. Clean and dry the
rotor if it fails that test. Then, repeat the test. If the rotor
fails the second insulation resistance test, it should be
replaced.
SECTION 2.4
DIAGNOSTIC TESTS
Page 41