Maker Pro
Maker Pro

Elliptical Resistance Brake Actuator Issue with RS485 Comm Back To Control Board


Jul 28, 2013
Jul 28, 2013
I buy and sell used fitness equipment, mostly ellipticals and exercise bikes. Many times the stuff I buy is in "as is" condition and needs repairs. I can fix most mechanical issues but by far the most common issue I find is with the resistance circuits. I'm here to try to find out more about what components make up this circuit.

Most every make and model of residential fitness equipment (bikes and ellipticals) use what appears to be the same basic system. Inputs from the console panel (resistance up, resistance down) are fed to a 6 volt B5K resistance motor over a 5 wire harness. 2 wires carry voltage to the servo motor, 2 wires carry power to the potentiometer and one wire carries the return signal voltage from the potentiometer back up to the panel to report the servo position (and hence, the position of the magnetic resistance brake system). I believe its this position signal that is to blame for most of the issues beyond simple motor failure which is easy to diagnose and fix.

What I think is occurring is that this positioning signal gets somehow corrupted or one of the circuit board components that are responsible for reading the potentiometer signal voltage gets out of sorts, resulting in console errors (usually an "E1") or simply no reaction from the resistance motor, despite audible feedback beeps from the resistance buttons on the control panel.

Here is a video that illustrates how the resistance system should work, and below that, I have a resistance motor control board in which exhibits the behavior I describe and I'm trying to troubleshoot to find the faulty board component:


The pin socket at top left is the 5 wire harness that leads to the resistance motor. To the right of that is the 4 wire harness connector that goes from this controller board up to the main console. The IC chips marked are ones that appear to trace to one or both of these pin sockets.

Rear of board above:



I've just tried to identify the components that appear to have obvious traces to the two i/o pin sockets. I'm not certain how to test these components or which I should test first as most obvious.

This particular board exhibits the following behavior: Everything works perfectly fine as long as the motor is not connected to load. In other words, the brake magnet cable is not attached to the servo motor. The motor turns to the exact expected position, feeds the expected 4.8 volts across the yellow and blue motor wires and the system startup of the machine passes. However, when the motor is connected to the brake cable, the voltage reading drops to 0.28 volts as if the circuit senses some overload condition and goes into a failsafe voltage.
Last edited: