Help with treadmill motor controler project Johnson MLH091PC

Thread Starter


Joined Mar 23, 2016
Hi there,
My AFG 3.1AT treadmill display & control console suddenly died, it receives power but there is no light or sound when I turn the treadmill on.
I don't want to spend $300-400 on a replacement board, and I don't want to try to fix it.
What I want to do is to control the running belt with a simple device. (probably a simple PWM circuit, a PIC or even a full blown Rpi project)
But first I need to know how to control this thing.
I couldn't find a schematic of the board (Johnson MLH091PC), and don't know how to reverse engineer it.

The 8 pins socket (JP2) is connected to the upper board, and has nothing written on it.

On the upper board the pins are identified as
So I'm guessing:
  • DA or DB must be used to PWM the main motor
  • (then I wonder what is controlling the elevation motor)
  • SAFE pins for connecting the safety switch
Right ?
Any advice, existing schematics for this board greatly appreciated.
Programming background, very basic electronic, can solder, I own a DMM and a dead treadmill

Thread Starter


Joined Mar 23, 2016
Ok I've found a chart that explains a bit more the pinout, but no detailed info. I still don't know how to control the motor.
I'm going to learn about RS485 differential signal.CableChart.png

Thread Starter


Joined Mar 23, 2016
Ok, this is not good news!
The board is controlled digitally using RS485 serial link. (so forget about simple PWM interface)
The protocol is not documented anywhere, and I can't analyze it (with one board being dead ).

So ,reluctantly, I put this project on hold until someone hopefully finds the specs. Or, until somebody has the same machine, the nohow, will and ... time to analyze and reverse engineer the protocol.


Joined Oct 22, 2014
Hi All,'s not as ugly as it appears. This is the JHT (Horizon) digital MCB. Before you go thru all the trouble to try to bypass the MCB, get ahold of me and I can get you one for about 80 refurbed. jatinahATrocketmailDOTcom

The question of the elevation...this is a stunningly stupid idea, but they decided to use 2 hall effect pickups inside that lift motor to tell the upper board it's moving, which direction, and at what "count" or position it is in.

They took the old single turn pot out of the lift, added 2 Hall pickups 180-degrees apart, added 31 support parts to the MCB, confused everyone and everything when that old style pot worked pristine, just to "watch that lift now"

Absolutely crazy bad idea! Now that upper must "remember" the "ticks" or count and add or subtract from setpoints and then compare and god forbid a servicer doesn't set that lift exactly right at install, as that will throw all setpoints off. When I saw this design come by my desk, I casually clocked out for the day, scratching my head....they took something easy , and completely mucked it all up...totally...I can get you a good lower tho

AND...the upper now has a Battery to "remember the counts" and to fail for users....ugh