Treadmill Problem

Thread Starter


Joined Apr 2, 2009
How are you Guys.
This problem in particular is directed to @MaxHeadRoom. I believe he has more experience in this.
First time in a long time a treadmill is driving me nuts.

I really dunno the model, but I can post pictures.
Problem : Motor speed just stays at start speed.

Findings :
No fault found so far in drive board. Can't say anything about the black coated driver PCB that is sticking vertically on driver side of PCB.
PSU voltages all remain stable. Power relay turns on when command comes.
All functions are working except the speed up. Display shows speed increasing but the motor stays at it's initial start speed.
RPM sensor switches between 0 and 5V.
Without sensor, console indicates low speed.

So I finally scoped it.
Traced the RPM all the way to uC. All good.
Traced the PWM all the way to uC. All good. ( All good means signal remains the same through out ).
The drive PWM goe via a transistor, an NOR gate and a schmitt inverter. The period and pulse remains same although inversion takes place when it pass via the gates. The Signal at uC is same as the drive opto coupler at the drive PCB. So in between I found no issues.
When I ground the PWM the motor stops.

The issue found was that the uC terminal PWM does not change it's duty cycle when the peed up command is given , although the display says speed is rising.

This thing has officially driven me crazy.

What are your thoughts. ?

Regards to all.

Thread Starter


Joined Apr 2, 2009
Here are the pictures for reference.
The scope signal shows the PWM dive at minimum speed.
The noise at 0V level comes when motor starts. Some how motor noise is being injected into the ground line.
All operations are normal except speed.

Because of the noise in the drive line I tried another method. The motor is powered be a separate PSU. The RPM is fed back into drive as it was before. Started the tead and it works normally but as before. But this time the PWM is clean, no noise.
Still the PWM drive does not change as speed is increased.