Mercury MerCruiser MCM 454 Mag MPI Service Manual page 377

CHARGING SYSTEM
RECTIFIER AND DIODE ASSEMBLY
NOTE: Failure of any component in tests following will require replacement of entire rectifier
assembly.
NEGATIVE (–) RECTIFIER
IMPORTANT: Rectifier MUST BE disconnected from stator for this test.
DO NOT use a test instrument with more than a 12 volt source (in the following test),
as rectifier may be damaged.
1. Connect one lead of an ohmmeter (set on R x1 scale) to negative (–) rectifier heat sink
and the other lead to one of the rectifier terminals. Note the reading.
2. Reverse leads and again note reading.
3. Meter should indicate a high or infinite resistance (no meter movement) when
connected one way and a low reading when connected the other. If both readings are
high or infinite, rectifier is open. If both readings are low, rectifier is shorted.
4. Repeat Steps 1 through 3 for two other rectifiers in heat sink.
5. Replace assembly if any of the rectifiers is shorted or open.
POSITIVE (+) RECTIFIER AND DIODES
DO NOT use a test instrument with more than a 12 volt source (in the following test),
as rectifier may be damaged.
1. Connect one lead of an ohmmeter (set on R x1 scale) to 1/4 in. stud on positive (+)
rectifier heat sink and the other lead to one of the rectifier terminals. Note the meter
reading.
2. Reverse leads and again note reading.
Index
Page 4C-22
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a - Heat Sink
b - Rectifier Terminal
c - Test These Two Rectifiers In The Same Manner
CAUTION
b
c
a
CAUTION
SERVICE MANUAL NUMBER 23
72147
90-861326--1 MARCH 1999