Case 580SR Service Manual page 979

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CHECK THE VOLTAGE LOWERINGS IN THE
CHARGING CIRCUIT
Voltage drop on insulated side
Check that the ignition is turned off (key on "off").
Z Disconnect the negative cable from the battery and
disconnect cable B+ (1) from the alternator.
Z Connect a millivoltmeter (4) between the positive
terminal of the battery and cable B+ (5) (positive
side on cable).
Z Connect an ammeter (2) between terminal B+ of the
alternator and cable B+ (negative side on cable).
Z Reconnect the negative cable of the battery and
connect a variable resistance (3) between the bat-
tery terminals by adjusting the cursor to the mini-
mum current draw (maximum resistance).
Z Start the motor and increase its speed to 2000 rpm.
Z Gradually reduce the resistance until the ammeter
shows 90 A.
Z Observe the millivoltmeter, which must not indicate
a value that is greater than 400 millivolts.
If the value exceeds 400 millivolts, the resistance of
the external circuit is too high. If the output value of
the alternator is not sufficient and the millivoltmeter in-
dicates a value that is less than 400 millivolts, an al-
ternator component is defective. Carry out the
operations described in the "Checking the alternator
components".
Z Stop the engine.
Voltage lower on ground side
Z Check that the ignition is turned off (key on "off").
Z Check the same circuit as the one in the previous
test, but by connecting the millivoltmeter (4) be-
tween the negative terminal of the battery and the al-
ternator body (negative side on body).
IMPORTANT: make sure that the variable resist-
ance (3) is in the minimum current draw position
(maximum resistance).
Z Start the motor and increase its speed to 2000 rpm.
Z Gradually reduce the resistance until the ammeter
(2) shows 90 A.
Z Observe the millivoltmeter, which must not indicate
a value that is greater than 200 millivolts.
If the value exceeds 200 millivolts, the resistance of
the external circuit is too high.
If the output value of the alternator is not sufficient and
the millivoltmeter indicates a value that is less than
200 millivolts, an alternator component is defective.
Carry out the operations described in the "Checking
the alternator components".
Z Stop the engine.
SECTION 55 - ELECTRICAL SYSTEM
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