4000PT Alternator Troubleshooting
If you suspect your StairMaster has a faulty alternator, perform the following tests to pinpoint the problem.
1. Test continuity of gray cable. Disconnect the gray cable from the back of the console. Using a paper clip formed into a U Shape, insert the ends of the paper clip to the pin sockets # 2 and # 4. Then start stepping. You should experience full pedal resistance. If there is no pedal resistance, either the gray cable or the alternator is bad.
2. Check alternator brushes. The brushes should be seated squarely on the commutator and should be worn evenly. Check for cracks and excessive wear. The brushes should be at least 3/8" long.
3. Check the commutator. Look for excessive wear on the copper commutator. If it is excessively grooved, the alternator should be replaced.
4. Check all wiring harnesses for wear. Bad electrical connections can cause alternator malfunction. With a continuity tester, check the continuity of all gray cable wires.
5. Check the alternator. Disconnect the black wire from the right side of load resister. (It is the same wire that connects to positive output terminal of the alternator.) Remove the brown wire from the field terminal. Make contact with the black wire you have disconnected to the spade connector of the field terminal. Step on the pedals of Stair-Master and start stepping. Resistance in the alternator should increase steadily. If the resistance does not increase, the alternator is bad.
When ordering an alternator be sure to identify its make and model number.