Treadmill DC motor receiving higher than rated voltage.

Thread Starter

minoush82

Joined Aug 2, 2020
2
Hello,

My treadmill stopped working (i.e. belt no longer moves) with a loud popping sound. When I inspected the motor-controller board I found a damaged 22 ohms resistor that I replaced. Then, I decided to see if the board works fine, so I put the board back and I used my DMM to measure the live voltage across the output ports where the motor wires usually go, and it measured 320V. The DC motor is labeled as 180V with horse power 1.1. Does this mean that the board is still faulty? I could not bring myself to connect the motor to avoid further damage -- in case it hasn't been damaged already.

What I noticed is that the controller board's output voltage is 0 when the machine is off; and when I turn it on and start raising the speed, the output jumps to 320V i.e. it does not reach that value gradually and seems oblivious to dashboard speed controls (except powering on, and raising speed from 0.0 km/h to 0.2 km/h).

I could not test the motor itself as I don't have lying around any DC power supply that I know can be used to test if the motor is fine. The brushes have comfortable length.

So to recap, from this description:
(1) Is my motor-controller board faulty? What should I inspect further? diodes? transistors?
(2) Will the 180V-rated motor be damaged if I connect it to the 320V output?
(3) How can I test the motor in isolation?
(4) Any further advice?

Many thanks.
 

MaxHeadRoom

Joined Jul 18, 2013
21,233
Run the motor on a automotive battery to test it, that usually shows up common problems.
But it sounds as though the switching device is shorted, Mosfet etc.
What is the Type/number of the motor board?
Max.
 

Thread Starter

minoush82

Joined Aug 2, 2020
2
Run the motor on a automotive battery to test it, that usually shows up common problems.
But it sounds as though the switching device is shorted, Mosfet etc.
What is the Type/number of the motor board?
Max.
Thanks a lot for your prompt reply,

The board number is FX-M 94V-0 E302652 (attached is a snapshot of the board). My Google search did not yield much on that board number. I also could not make sense of the prefix that looks like a vertically-mirrored R followed by perhaps a U and a solid triangle.

So should I test/replace the MOSFETs? Anything else? bipolar transistors and diodes too? Do I start with the region around the burnt resistor?

I did some "in-circuit" testing using my DMM which is the only device I have.
- Most ceramic resistor values were within range of their color-coded values.
- I could not check the values of ceramic resistors connected to capacitors because the readings were unstable.
- I checked that diodes only conducted in one way.
- Two of the bipolar transistors have their base shorted to their collector. In one of the two, there is a board track between the base and collector so it is by design I guess, but in the other there was no visible board track that shorts the base and the collector. Could this be (part of) the problem? I mean, is there no circuit configuration that would make the base and a collector of a transistor shorted permanently?

Thanks,
Amine.
 

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