Volvo Penta D2-55 Workshop Manual page 86

Group 30 Electrical system
84
Checking the rotor winding
Once the regulator and brushes have been removed, it
is possible to measure the resistance of the rotor
windings.
Set the measurement instrument to position Ω. Make
sure the probes have good contact with the slip rings.
The rotor resistance should be 3.0-5.0 Ω.
Also check for grounding faults by measuring between
the slip rings and ground.
Removing the diode bridge
In order to check the diode bridge and stator windings,
the diode bridge should be removed.
Unsolder the three stator windings. Do not use too
much heat as this can damage the diodes. Undo the
nuts (note how the nuts and washers are fitted).
Checking the diode bridge
Set the multimeter to position "Diode test". Be very
sure that you have good probe contact for all mea-
surements.
Checking B+ diodes
1. Connect the multimeters positive probe to one of
the stator winding's connections (1-2-3). Then
connect the instruments negative probe to the di-
ode plate B+ connection. Read off the instrument.
A normal value should be between 450 and 650
mV which is the voltage drop across the diode.
Any other value indicates a faulty diode.
2. Check the other B+ diodes by moving the positive
probe to the other connections (1-2-3).
3. Then check the B+ diodes in the opposite direc-
tion by reversing the positive and negative
probes. Perform the same measurements as
above. The instrument should show a one "1" with
these measurements (furthest to the left). Any
other value on the instrument indicates a faulty di-
ode.