Among the most popular exercise machines sold on the market today, the Stairmaster 4600, 4400 and 4000PT stair climbers have three electrical components that are responsible for the majority of troubleshooting calls. The alternator, diode, and resistor are the heart and soul of the Stairmaster 4600/4400PT and often cause resistance levels to drop, leading to performance issues.
Tools needed:
7/16″, 3/8″ and 1/4″ nut drivers. 4″ piece of wire with alligator clips attached to each end and a multimeter,
Symptom:
The Stairmaster loses all resistance when you step on the pedals.
Alternator test:
First, remove the machine from its power source. Then remove the side panels so you have a clear view of the alternator. On the back of the alternator, remove the black wire from terminal B+ (marked POS). Remove the brown wire from the field terminal. You will need a 4″ long cable with alligator clips attached to each end of the cable. Connect the cable to the B+ (POS) terminal and to the field terminal, step on the machine for 10-15 seconds, if full resistance is present, the alternator has correct current flow. If there is no resistance, the next item to check is the alternator brushes. The brown square plate with two machine screws is the brush cover. Remove the two machine screws with a nut ¼”. driver and remove the brushes from the alternator. There should be a ¼” brush or more, or less, and the alternator brushes should be replaced first. If the proper amount of brush is available, replace the alternator.
test diode:
Remove the brown wire and diode from the alternator field terminal and set the multimeter to the ohms setting. Attach one lead to each end of the diode, then reverse the leads. A good diode will indicate a high reading in one direction and a lower reading in the opposite direction. Replace the diode if both readings are high or if both readings are low.
Resistance test:
Remove one lead from the load resistor and place one lead from the multimeter, one from each threaded post on the resistor. If the multimeter does not read 0.5 ohms, replace the resistor. As with any maintenance procedure, always consult your owner’s manual or seek the advice of a qualified repair technician.