Component Testing - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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CHARGING SYSTEM

Component Testing

1. Test rotor field circuit for opens, shorts or high resistance (Test 1), using an ohmmeter

(set on R x1 scale), as follows:

Testing Rotor Field Circuit

a. Connect one ohmmeter lead to each slip ring.

b. Ohmmeter reading should be 4.2 to 5.5 ohms with rotor at room temperature

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

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70-80 F (21-26 C).

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.

Field Winding Leads

SERVICE MANUAL NUMBER 23

90-861326--1 MARCH 1999

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