How to Troubleshoot Electrical System on Stairmaster 4000PT

Stairmaster Stepper 4000PT Electrical SystemTroubleshooting

Does your Stairmaster 4000PT stepper have some power problems and you are unsure where to begin? Don't let power problems with your machine cause an outage in your workout. A few simple tests can tell you the state of affairs of your electrical system.

The testing requires a multimeter and the knowledge of how to use a multimeter.

WARNING: TO REDUCE THE RISK OF ELECTRICAL SHOCK, A QUALIFIED ELECTRICAL TECHNICIAN SHOULD PERFORM ALL ELECTRICAL TESTS THAT INVOLVE CHECKING AC POWER.

• Verify that the AC wall outlet is supplying the correct power in one of two ways:
   Use the AC setting on your multimeter to verify that the AC line voltage is between 100 and 120 VAC (or between 220 and 240 VAC, if applicable) at the AC wall outlet.
  Or
   Plug in an alternate AC-powered device. Use a lamp, fan, or radio for example.  If the device does not work when plugged into the AC wall outlet, consult an electrician for help with the outlet. Retest the AC wall outlet after any repairs.
• With a known good outlet, plug the AC cord from the power supply into the AC wall outlet.
• Depending on the style or age of the power supply, it may have an LED light on the side and a reset button. This green LED should now be on.  If the light is not on, reset the circuit breaker on the power supply by pressing the button. If the LED still does not light up, test power from the power supply before replacing the power supply. Some power supplies do not have an LED light or circuit breaker.
• Disconnect the DC cable from the machine. The DC cable connects the power supply to the machine. With your multimeter set to DC voltage, check for 15-17 VDC in pins #1 (positive) and #2 (negative) of the DC cable.   Replace the power supply if the voltage reading is outside the specified range.
• Remove the side covers.
• Reconnect the DC cable to the side panel power connector and locate the black and white wires on the backside of the power connector.
• Follow the white power connector wire to the alternator and unplug it from the main cable white wire.
• Set your multimeter to DC voltage. Connect the positive lead of your multimeter to the white wire from the power connector and touch the grey casing of the alternator with the negative lead of your multimeter.
• DC voltage measured should be 15-17 VDC. Replace the power connector if the voltage is outside the specified range.
• Reconnect the two white wires.
• Locate pins #1 (positive) and #9 (negative) in the main cable connector that plugs into the console and measures DC voltage.
• DC voltage measured should be 15-17 VDC.  Replace the main cable assembly if the voltage is outside the specified range.
• If all voltage readings have been within the specified range and the console will not power up, the console should be replaced.
• Check for loose wiring connections on the alternator, diode, and load resistor.
• Preform the Positive Output to Field test:
  Turn the power off.
  Remove the black wire from the B+ terminal on the alternator.
  Remove the brown wire from the field terminal on the alternator.
  Place alligator clips on the B+ terminal and the field terminal of the alternator.
  Step on the machine for 15-20 seconds.
  If full resistance is achieved during this time, your alternator has the correct current flow.
• Remove the brown wire and diode from the field terminal of the alternator and set your multimeter to the lowest resistance setting.
• Place one lead from the multimeter on each end of the diode, and record the number shown on the multimeter. Then reverse the leads and record the number shown.
• A diode in proper working condition will show a high reading in one direction and a low reading when the leads are reversed.
• Replace the diode if the readings recorded are both high or both low.
• Remove one wire from the load resistor and set your multimeter to the lowest resistance setting.
• Place one lead from the multimeter on each of the threaded posts on the load resistor. Record the number shown.
• A load resistor in proper working condition should read approximately 0.5 ohms.  If the number recorded is outside the specified range replace the load resistor.