Filter
Top Products
SSeeccttiioonn 77
DDIIAAGGNNOOSSTTIICC TTEESSTTSS
7. Inspect the slip rings.
a.If slip rings appear dull or tarnished they may be
cleaned and polished with fine sandpaper. DO
NOT USE ANY METALLIC GRIT TO CLEAN
SLIP RINGS. (A 400 grit wet sandpaper is rec-
ommended).
b.After cleaning slip rings, blow away any sandpa-
per residue.
RESULTS:
1. Replace bad brushes. Clean slip rings, if necessary.
2. If brushes and rings are good, go to Test 11.
TEST 11- CHECK ROTOR ASSEMBLY
DISCUSSION:
During the “Fixed Excitation Test” (Test 4), if AC out-
put voltage did not come up to about one-half rated
volts, one possible cause might be a defective Rotor.
The Rotor can be tested for an open or shorted condi-
tion using a volt-ohm-milliammeter (VOM).
Also see Chapter Three, “INSULATION RESIS-
TANCE TESTS”.
PROCEDURE:
Gain access to the brushes and slip rings. Disconnect
Wire 4 and Wire OF from their respective brushes
and remove the brush holder. Then, test the Rotor as
follows:
1. Set a VOM to its “Rx1” scale and zero the meter.
2. Connect the positive (+) meter test lead to the positive (+) slip
ring (nearest the Rotor bearing). Connect the common (-) test
lead to the negative (-) slip ring. Read the resistance of the
Rotor windings, in OHMS.
ROTOR RESISTANCE *
MMOODDEELL:: OOHHMMSS
QP55 4702/4703 14.88Ω
QP65 4704/4705 10.81Ω
QP75 4706/4707 14.50Ω − 16.0Ω
* Resistance values In ohms at 20° C. (68° F.). Actual readings
may vary depending on ambient temperature. A tolerance of
plus or minus 5% is allowed.
3. Set the VOM to its “Rx1 K” or “Rx10,000” scale and zero the
meter.
4. Connect the positive (+) meter test lead to the positive (+) slip
ring, the common (-) test lead to a clean frame ground (such as
the Rotor shaft). The meter should read “Infinity”.
RESULTS:
1. Replace the Rotor if it fails the test.
2. If Rotor checks good, perform “Insulation Resistance Test,” on
Page 14.
Figure 7-8. – Rotor Assembly
TEST 12 - CHECK MAIN CIRCUIT BREAKER
DISCUSSION:
The main circuit breaker on the generator panel must
be closed or no output to the load will be available. A
defective breaker may not be able to pass current
even though it is in the “ON” position.
Figure 7-9. – Main Breaker (Typical)
PROCEDURE:
Set the coach main breaker to it’s “OFF” position.
Check that the appropriate main breaker on the gen-
erator panel is set to its “ON” (closed) position. Set a
VOM to measure resistance and use it to check for
continuity across the breaker terminals.
Page 44