GMC 1976 ZEO 6083 Maintenance Manual page 721

24C- 4 4 ONAN MOTOR GENERATOR
Figure 84-Armature Open Test
Using on Ohmmeter: Disconnect external leads
and connect ohmmeter leads to F1 (+) and F2 (-).
Resistance in the windings should read 28 .8 ohms
(± 3%) for the 4KW and 38 ohms (± 3%) for the
6K _ W.
Using a Test Lamp Set: Disconnect external
leads and touch test prods to F1 and F2. The lamp
should light. If not, field winding is open and must
be replaced.
TESTING FOR GROUNDS
Figure 85-Testing Field Windings
Check terminal ends closely for loose connec-
tions. These can be fixed easily without replacing the
whole assembly .
TESTING BRIDGE RECTIFIER
To accurately test bridge rectifier proceed as fol-
lows:
1 . Loosen No. 8-32 screw to remove bridge rec-
tifier assembly (See figure 86 for location).
2. Disconnect the nylon connector from bridge
rectifier assembly, noting the polarity marking of
bridge rectifier assembly and connector.
3. Pull out from end bell and remove bridge rec-
tifier from its case .
CAUTION: Note that connector can only be
mounted in one direction.
4. Use an ohmmeter to test bridge rectifier. Set
the ohmmeter dial to R x 1 scale.
5. Now place meter leads on points shown in
Figure 87 and note readings from following table :
* -+ 10% - Readings taken at 70 F.
6. If any tests do not agree with the above read-
ings, install a new bridge rectifier.
TESTING FOR OPENS A-1662
BLACK
LEAD
RED
LEAD
RE-
SISTANCE
A
B * 8 ohms
A
D *8 ohms
B
C
*8 ohms
D C * 8 ohms
B A Infinity
D A Infinity
C B Infinity
C D Infinity