Case 580SR, Service Manual

Page: 982 / 1068

154 SECTION 55 - ELECTRICAL SYSTEM
RECTIFIER - CHECKING THE POSITIVE /
NEGATIVE DIODES
Check each of the six diodes separately by proceed-
ing as follows:
Z
Connect a multimeter (2) in series with one of the
diodes. Place one wire of the multimeter on the
connecting pin (1) of the diode and the other wire
on the plate where the diode is installed.
Z
Note down the value of the resistance indicated by
the multimeter. Reverse the wires of the multime-
ter.
Z
The multimeter should indicate infinite resistance
(open circuit) only during the first half of the test. If
this check reveals that a diode is defective, replace
the entire rectifier.
RECTIFIER - CHECKING THE EXCITATION
DIODES
Check each excitation diode separately by proceed-
ing as follows:
Z
Connect a multimeter (2) in series on the excitation
diode module. Place the negative wire on terminal
L (1) and the other wire on the connection of each
excitation diode (3).
Z
Note down the value of the resistance indicated by
the multimeter. Reverse the wires of the multime-
ter.
Z
The multimeter should indicate infinite resistance
(open circuit) only during the first half of the test. If
this check reveals that a diode is defective, replace
the entire rectifier.
STATOR - CHECKING THE CONTINUITY OF THE
WINDING
Check each excitation diode separately by proceed-
ing as follows:
Z
Connect the wires of the ohmmeter (3) between
wires A, B and C (2). The resistance between each
of the wires must be low (0.1 W). If the resistance
is greater than this value, it indicates a possible
break in the winding, i.e. an open circuit. A lower
value (0.0. for example) indicates a short circuit in
the winding. If the result of this check is not satis-
factory, replace the stator (1) and its casing.
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