Flir Camera analysis of Treadmill Motor Control Board Hot Spots

Thread Starter

Scott Blanchard

Joined Jul 28, 2019
I buy and sell pre-owned fitness machines (treadmills, ellipticals and exercise bikes). Over the past several months I've accumulated several machines that have circuit board issues. Up until now, I've just been replacing whole boards when there is a problem. However, I'm at the point where I'd like to try to see if I can repair some of these boards rather than replacing them. It would also be great to save a little money, as well as the sense of accomplishment at learning to fix them.

I've purchased a thermal imaging camera that works with my iphone. Its a Flir One Pro. I've included some shots below of this current project. Its a Horizon wt751 treadmill that turns on, console lights, incline works, everything looks fine until you press the START button to get the belt moving, it does the 3, 2, 1 countdown, the relay clicks in, but then nothing happens.

Hoping someone here can help teach me how to identify and repair the components at fault. Here are the pics of the motor control board with the 3 areas of interest circled in red:

Horizon Treadmill.jpg

Thermal image below of cold board before turning on power. Yellow areas here are just reflective surfaces:

Below, the treadmill has power and the heat threshold has been turned up to 150 degrees F. The 3 areas of concern as showing high heat signatures in yellow:


They are from top left, an IC identified with writing as:

1) Top left component > 78M05 (voltage regulator?)
2) middle component > UC3842BN (Switching Controllers 0.5mA Current Mode)
3) Bottom left > R15 and R16 Resistors




Thread Starter

Scott Blanchard

Joined Jul 28, 2019
What would next steps be? Are the resistors possibly OK or should they not be getting that hot? Which of the 3 components would you test first and how? I have a multimeter and know a bit about how it works for testing continuity and voltage. Thanks in advance.


Joined Jul 18, 2013
Not familiar with that particular board, but have you tried the motor to see if it turns OK, using a Automotive battery etc, did you try measuring the output of the 7805 for 5vdc?

Thread Starter

Scott Blanchard

Joined Jul 28, 2019
I'm going to try running the motor on an 18v Ryobi cordless battery and make sure its operational. However, once I saw the Flir scan, I was pretty sure one of those components was shorted on the board. I'll also test voltage on the 7805.


Joined Mar 11, 2019
I have no knowledge of treadmills so take what I say as general information,
but.... Just because you hear a relay click does not mean its working properly. Does this relay supply the motor? Have you tested to see if the relay is supplying its load? It seems like the control board is working to me from your posts and its just the motor is not turning on. I would start by checking the power feed at motor and if no power is present work backwards from there.
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