Where to start debugging dead Treadmill Control board

Discussion in 'General Electronics Chat' started by ebenze, Feb 14, 2013.

  1. ebenze

    Thread Starter New Member

    Feb 14, 2013

    I've got a Sears treadmill that has abruptly stopped working. Neither the carpet motor turns nor does the elevation motor. The control panel lights up, but pressing any of the buttons does not do anything. ie: trying to select a program doesn't work, pressing OK doesn't do anything, pressing speed controls don't do anything, nor does pressing the buttons for elevation.

    The control board that seems fairly simple, but I'm not sure how/where to start debugging this. I presume that most treadmills follow similar logic board designs so I'm hoping that someone might recognize the symptoms and have some ideas.

    The elevation motor is a 120VAC motor, which I've checked and confirmed works properly. The carpet motor is a 110VDC motor which I have been unable to test (where do I get a 110VDC source from?!), but would be surprised to see not working.

    When I first turn the treadmill on by the master power switch, I hear a "click" - the primary relay engaging (it's an 832A-1A-C relay). However, that's about it. I'm not sure what to check next.

    Most importantly, I don't understand the symptoms. If the panel doesn't respond to a user pressing a button - might I be looking in the wrong place? Might it be something flaky in the panel instead of the controller board? Is there a way I can validate that the controller board works?

    I'm attaching a picture of the controller board, and of the overall circuit diagram. I'm also interested in the nomenclature of the panel's connector (JK1). I do not recognize what VR1 means.

    I realize that this is a very open ended question, so I would appreciate any thoughts/suggestions/advice as to how to tackle this. I contemplated replacing the controller board, but Sears wants over 400$ for the board, so that is out of the question.


  2. SPQR


    Nov 4, 2011
    Well, it might be time for a volt meter.

    Connect the black to ground, and use the red probe to CAREFULLY touch strategic points on the wires TO the board, EXITING the board, and some "obvious" points on the board.

    Draw a diagram of where the voltages are and how much they are.
    Then perhaps post it.
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Check to make sure the safety tether (key) is plugged in correctly. This key is supposed to be warn by the user and stop the motors if the user is ejected.

    Since most people do not use the teather, most people forget it is there and when it eventually gets bumped out of place the unit stops working and nobody remembers how to "fix" it.
    SPQR likes this.
  4. PackratKing

    Well-Known Member

    Jul 13, 2008
    In your circuitry, you have a large, likely full-wave-bridge monolithic rectifier, which provides the 110V DC for your carpet motor, and is probably shorted.

    I would venture, that this rectifier is not on an adequate heat sink.