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3. Open Test. Set meter to read low resistance (R x ohms).
Holding one meter lead on surface of slip ring No. 1,
touch other meter lead to surface of slip ring No. 2 while
observing the meter. Meter should indicate continuity (low
resistance - less than one ohm is typical). If the meter in-
dicates open circuit (infinite resistance) part of armature
winding is open. This may be caused by a repairable de-
fect in the connection at the slip ring, however generally
an open armature will have to be replaced. Continue
reading the continuity between slip ring No. 2 to No. 3 and
No.2 and No.4. All the slip rings should have continuity to
slip ring number 2, the neutral ring.
Testing Rectifiers
The field excitation is supplied through a full wave bridge
rectifier. This type of rectifier has four terminals, two AC, a
DC positive and a DC negative.
A rectifier may be tested in the following manner:
1. Tag and disconnect all leads from rectifier.
2. Connect the red ohmmeter lead to the positive DC (+)
terminal.
3. Connect the black lead to each of the AC terminals in turn.
Either a high or low resistance reading will be obtained.
4. Reverse the meter leads, black lead to the DC POS (+)
and red to the AC terminals, each in turn. An opposite
reading should be observed.
5. Connect the red ohmmeter lead to the negative DC (-)
terminal.
6. Connect the black lead to each of the AC terminals in turn.
Either a high or low resistance reading will be obtained.
7. Reverse the meter leads, black lead to the DC NEG (-) and
red to the AC terminals, each in turn. An opposite reading
should be observed.
8. Check each terminal to the case. An open circuit (very
high resistance) reading should be observed. A battery
powered test light may be used. Follow the same proce-
dures described above. A good diode element will allow
current to pass to the light in the test lamp in only one di-
rection.
9. If the rectifier fails any of the above tests, it should be
considered defective and replaced.
Condenser Testing
Condensers are built into the generator circuit to minimize
radio interference during operation. If a condenser shorts
out, it will also short out the generator output. To determine
whether a condenser is shorted, stop the generator and
disconnect the condenser lead wire from the brush holder.
Using a multimeter on the R x 100 scale, check the resis-
tance of the condenser. Normal response is a sharp swing
of the meter towards low resistance and then a steady rise
towards high resistance (open circuit). If the capacitor is
shorted it will show as a constant low resistance.
Otherwise, restart the generator without the capacitor con-
nected to recheck the generator for output. If the generator then
provides power, the condenser was at fault and should be
replaced. (If the generator doesn't provide power, the problem
was not caused by that condenser, reconnect the lead wire).
If these tests have not located the trouble, remove the
armature and have it tested for opens, shorts, and grounds
on a growler.
