MerCruiser 305 CID (5.0L) Service Manual page 327

CHARGING SYSTEM
c. If reading is high or infinite (no meter movement), high resistance or an open exists
d. If reading is low, a short exists in the field circuit. Inspect slip rings to be sure that
2. Test rotor field circuit for grounds (Test 2), using an ohmmeter (set on R x1 scale) as
follows:
a. Connect one lead of ohmmeter to either slip ring and the other lead to rotor shaft or
b. Meter should indicate no continuity (meter should not move).
c. If continuity does exist, complete rotor assembly must be replaced.
IMPORTANT: If alternator has output at low speeds, but no output at high speeds,
rotor field winding may be shorting or grounding out, due to centrifugal force.
Replace rotor if all other electrical components test good.
STATOR
IMPORTANT: Stator leads MUST BE disconnected from rectifier for this test.
1. Test stator for grounds (Test 1), using an ohmmeter (set on R x1 scale) as follows:
a. Connect one lead of ohmmeter to one of the stator leads and the other lead to stator
b. Meter should indicate no continuity (meter should not move). If continuity does exist,
2. Test for opens in stator (Test 2), using an ohmmeter (set on R x1 scale) as follows:
a. Connect ohmmeter between each pair of stator windings (three different ways).
Index
Page 4C-12
in the field circuit. Check for poor connections between field winding leads and slip
ring terminals. If cause for open or high resistance cannot be found, connect ohm-
meter directly to slip ring terminals. If correct reading is now obtained, or if reading
is still high or infinite, replace complete rotor assembly.
they are not bent and touching outer slip ring. Also, be sure that excess solder is not
shorting terminals to aft slip ring. If cause for short cannot be found, unsolder field
winding leads from slip ring terminals and connect ohmmeter directly to leads. If
correct reading is now obtained, or if reading is still low, slip rings and rotor field
windings are shorted, and complete rotor assembly must be replaced.
a - Field Winding Leads
b - Slip Rings
c - Rotor Shaft
d - Pole Pieces
pole pieces.
frame. Be sure that lead makes good contact with frame.
stator is grounded and must be replaced.
d
c
SERVICE MANUAL NUMBER 24
b
a
73112
90-861327--1 OCTOBER 1999