26SI Series Alternator – Rectifier – Test

The illustrations below show The M1 series alternator (35 amps).

Negative Diode Check




    Illustration 1 g00825570

    Negative Diode Check

    (9) Stator leads

    (10) “B-” terminal

    (11) Stator lead connection

  1. Disconnect all stator leads (9) from the rectifier.
  1. Set the multimeter to the diode scale.
  1. Connect the multimeter leads across one stator lead connection (11) and “B-” terminal (10) .
  1. Record the multimeter reading.
  1. Reverse the multimeter leads.
  1. Record the multimeter reading.

    Expected Result: One reading is “0L” and the other reading is .4 to .9 volts.

    Results:

    OK – One reading is “0L” and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 1 through 6 for the other stator lead connections (11). STOP.

    NOT OK – Both readings are “00”. The diode is shorted. Replace the rectifier. STOP.

    NOT OK – Both readings are “0L”. The diode is open. Replace the rectifier. STOP.

    Note: The 35 amp alternator has three negative diodes and three stator leads. The remaining alternators have four negative diodes and four stator leads.

Positive Diode Check




    Illustration 2 g00825571

    Positive diode check

    (9) Stator leads

    (11) Stator lead connection

    (12) “B+” terminal

  1. Stator leads (9) remain disconnected from the rectifier.
  1. The multimeter remains on the diode scale.
  1. Connect the multimeter leads across one stator lead connection (11) and “B+” terminal (12) .
  1. Record the multimeter reading.
  1. Reverse the multimeter leads.
  1. Record the multimeter reading.

    Expected Result: One reading is “0L” and the other reading is .4 to .9 volts.

    Results:

    OK – One reading is “0L” and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 1 through 6 for the other stator lead connections (11). STOP.

    NOT OK – Both readings are “00”. The diode is shorted. Replace the rectifier. STOP.

    NOT OK – Both readings are “0L”. The diode is open. Replace the rectifier. STOP.

    Note: The 35 amp alternator has three positive diodes and three stator leads. The remaining alternators have four positive diodes and four stator leads.

Exciter Diode Check




    Illustration 3 g00825576

    Exciter Diode Check

    (2) Wire assembly

    (9) Stator leads

    (11) Stator lead connection

    (13) Exciter diode output

  1. Stator leads (9) remain disconnected from the rectifier.
  1. The multimeter remains on the diode scale.
  1. Disconnect wire assembly (2) from the rectifier.
  1. Connect the multimeter leads across one stator lead connection (11) and exciter diode output (13) .
  1. Record the multimeter reading.
  1. Reverse the multimeter leads.
  1. Record the multimeter reading.

    Expected Result: One reading is “0L” and the other reading is .4 to .9 volts.

    Results:

    OK – One reading is “0L” and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 3 through 7 for the other stator lead connections (11). STOP.

    NOT OK – Both readings are “00”. The diode is shorted. Replace the rectifier. STOP.

    NOT OK – Both readings are “0L”. The diode is open. Replace the rectifier. STOP.

    Note: The 35 amp alternator has three exciter diodes and three stator leads. The remaining alternators have three exciter diodes and four stator leads. If the alternator has four stator leads, do not test the stator lead with the black mark. The stator with the black mark lacks an exciter diode. Ignore the result for that stator lead. See Systems Operation, “Component Description” for more information on the stator and on the stator leads.

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