Alternator - Delco 21SI Caterpillar


Rectifier - Test

Usage:

980C 13B



Illustration 1g00721624

(1) Positive diode contacts

(2) Positive heat sink

(3) Negative diode contacts

(4) Negative heat sink

Positive Diode Check

Note: Do not overstress the contacts of the diodes. Only bend the contacts when it is necessary.

  1. Bend all three positive diode contacts (1) away from the studs. The contacts (1) should not be touching the positive heat sink (2) .

  1. Set the multimeter to the diode scale. Connect the multimeter black lead to the positive heat sink (2). Connect the multimeter red lead to one of the positive diode contacts (1). The multimeter reading should be between 0.4 VDC and 0.9 VDC.

  1. Repeat step 2 for the remaining two positive diode contacts (1). If the multimeter reading is not between 0.4 VDC and 0.9 VDC for each positive diode, then replace the rectifier.

  1. Set the multimeter to the diode scale. Connect the multimeter red lead to the positive heat sink (2). Connect the multimeter black lead to one of the positive diode contacts (1). The multimeter reading should be "OL".

  1. Repeat step 4 for the remaining two positive diode contacts (1). If the multimeter reading is not "OL" for each positive diode, then replace the rectifier.

Negative Diode Check

Note: Do not overstress the contacts of the diodes. Only bend the contacts when it is necessary.

  1. Bend all three negative diode contacts (3) away from the studs. The contacts (3) should not be touching the negative heat sink (4) .

  1. Set the multimeter to the diode scale. Connect the multimeter red lead to the negative heat sink (4). Connect the multimeter black lead to one of the negative diode contacts (3). The multimeter reading should be between 0.4 VDC and 0.9 VDC.

  1. Repeat step 2 for the remaining two negative diode contacts (3). If the multimeter reading is not between 0.4 VDC and 0.9 VDC for each negative diode,then replace the rectifier.

  1. Set the multimeter to the diode scale. Connect the multimeter black lead to the negative heat sink (4). Connect the multimeter red lead to one of the negative diode contacts (3). The multimeter reading should be "OL".

  1. Repeat step 4 for the remaining two negative diode contacts (3). If the multimeter reading is not "OL" for each negative diode, then replace the rectifier.

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