Testing Alternator of Stairmaster Steppers, 4400CL,4600CL,SC916

The video demonstrates that on a Stairmaster stepper with no resistance, the pedals will fall to the floor. The steps covered can be used on stepper models including the 4400CL, 4600CL, and SC916.

Testing the alternator and checking that the alternator brushes are working properly is the recommended action.

Tools Needed:

  • 1/4" Nut Driver or Wrench


  1. Begin by disconnecting the brown wire from the Field terminal of the alternator and the white wire from the B+ or POS terminal of the alternator.
    1. The wiring sticker should help you to identify the designated terminals.
  2. A jumper wire is needed to proceed with this test. (A jumper wire can be fashioned from wire with slip-on connectors crimped to each end or the jumper can be a normal piece of wire with the coating stripped from each end. The designated terminals have a small hole that the stripped end of the wire can be threaded through to create the jumper.)
  3. Connect one end of the jumper wire to the B+ or POS terminal and the other end to the Field terminal.
    1. Step on the unit for about 10-15 seconds to verify resistance.
    2. If no resistance between the B+ or POS and Field, this normally indicates that the alternator brushes are worn or damaged.
  4. Remove the jumper wire and then remove the alternator brushes for further inspection.
    1. Using the 1/4" driver or wrench, remove the two bolts from the brush cover.
    2. Once the bolts are removed, pull on the Field terminal to remove the alternator brushes.
  5. Inspect the alternator brushes.
    1. The brushes should be smooth and free of cracks, nicks, and breaks.
    2. The brushes are spring-loaded; Confirm when pressed that the brush will spring back to position.
    3. Replace the brushes if necessary.
  6. When re-installing the alternator brushes to the alternator, the brushes will face down toward the inside of the alternator. (Due to the brushes being spring-loaded, it may be necessary to press the brush into its housing for ease of installation and to avoid damaging the brush.)
  7. Test the unit after replacing the alternator brushes.
    1. Reconnect the jumper wire to the B+ or POS terminal and the Field terminal.
    2. Step onto the unit and verify resistance.
      1. In this example, the alternator brush replacement was all that was necessary to correct the resistance problem.
  8. With resistance verified, it is time to remove the jumper wire and reconnect the white wire to the B+ or POS terminal and the brown wire to the Field terminal.
  9. Make sure all cables are connected (including the console cable) and this completes the alternator test.
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