HEAVY DUTY ALTERNATORS
Figure 16 - Negative Heat Sink Tests.
2.
Reverse the test leads so that the positive test
lead is connected to the negative heat sink.
Touch the negative lead to each of the three
diode terminals (Test 2, Figure 16). A low
resistance reading should be obtained, and if a
test light is being used, the lamp should light. If
high resistance is indicated or the lamp does not
light, the diode is open. See IMPORTANT.
IMPORTANT - WHEN MAKING DIODE TESTS, SOME
OHMMETERS MAY INDICATE RESULTS OPPOSITE
OF THOSE SHOWN IN TEXT (I.E. A HIGH
RESISTANCE
WHEN
TEXT
CALLS
FOR
LOW
RESISTANCE, ETC.). REGARDLESS OF THIS, EACH
DIODE SHOULD GIVE ONE HIGH READING AND ONE
LOW READING, IF BOTH READINGS ARE THE
SAME, DIODE IS FAULTY.
If a shorted or open diode is detected in the preceding
tests, the entire heat sink assembly should be replaced.
Heat sinks supplied as service replacements may differ
slightly in thickness or general appearance from the
original parts. This will in no way impair their
interchangeability or reliability. To obtain the maximum
serviceability, several different assemblies may be used
as replacements. These will be listed in the appropriate
parts list.
CAPACITOR TEST
The capacitor connected across the heat sinks may be
tested on a capacitor tester if available. Its value is .5
MFD, and 200 working volts D.C.
In the absence of a capacitor tester, the unit may be
checked for shorts by means of an ohmmeter connected
across the terminals. A low resistance reading indicates
a shorted or leaking capacitor which should be replaced
(See Figure 17).
Figure 17 - Testing Capacitor.
VOLTAGE REGULATOR TEST
The regulators used in these alternators cannot be
tested with ordinary test equipment. The easiest way to
check a regulator is to install it in an alternator which is
known to be in good working condition. Perform the
voltage adjustment procedures shown in VOLTAGE
REGULATOR ADJUSTMENT. If the alternator output
cannot be modified or if the output voltage is unstable,
the regulator must be replaced.
ROTOR TEST
The rotor should be checked for grounds and proper coil
resistance with an ohmmeter.
1.
With the ohmmeter connected between the rotor
shaft and either slip ring, no reading (infinity)
should be obtained. If an ohmmeter reading
other than infinity is obtained, the rotor coil is
grounded and the rotor must be replaced (See
Figure 18).
Figure 18 - Rotor Coil Ground Test.
CTS-4043A - Chapter II - Page 8
