Troubleshooting Treadmill Motor Control Board - Fuse & Mosfet keeps blowing (RESOLVED)

Discussion in 'Technical Repair' started by CobraL0rd, Jan 20, 2017.

  1. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
    39
    1
    I'm trying to find out what is wrong with my treadmill LifeGear 97370 Power Track Pro. I will describe everything as detailed as i can, to give more insight into the situation in order to figure out what's wrong. I have this treadmill for about 3 years now and have literally put hundreds of km's of sprinting @ 16mph into it (intermittent sprinting exercises). I couldn't be happier with it and it was actually quite cheap.

    About 2 weeks ago while i was running on the treadmill (as usual) i heard a sudden bump and i found out that the fuse flew. First i tested out the motor and found out it was running properly (from both directions) under the power of a 12V battery. I also run another test. By moving the belt by hand, once with the motor intact and the other with the motor's leads shorted. In the second case the belt was turning much harder, which clearly indicates the proper working condition of the motor (induced anti-EMF preventing motor from turning smoothly). Thus, i realized that the problem lies in the MCB.

    I first did a quick inspection in the circuit board's backplane (for which i will post an image) and checked for any black marks under the component leads and for any blown, malformed top surfaces in the electrolytic caps. I found out that the MOSFET's leads as well as some power resistor's ones were totally blackened. Thus, by checking the MOSFET IRFP460 i realized it was shorted and thus the culprit. I'm not sure about those power resistors. More on that later. I also removed some thermal paste here and there, but i shouldn't have and i plan to apply more. So I went ahead and ordered another MOSFET and replaced it. The treadmill was running again (with a few hiccups in speed) and it did so for about 20 minutes. Then the fuse (which i too of course replaced with an appropriate slow blow fuse @ 12A) blew up again and so did that same MOSFET. (I later realized that i should have connected the MOSFET in a better way to the circuit along with it's heat sink, but i don't think this caused it to blow.)

    To my frustration i had to pay more attention to all the components. I have to find out what is causing this power surge. So i checked all resistors, diodes, the 1 zener diode, the bridge rectifier (KBPC2506W), the power relay (HONGFA HF2150). What i didn't check are the various other IC's, just because they seem fine. All the caps, resistors, diodes, the bridge, the transformer measure to their nominal values. I didn't desolder every single one, but i figured i didn't have to do it for each, since the readings from in circuit were already pretty good. With the exception of one diode (labelled D1 as you can see in the image), which is to the relay. This one showed bizarre readings. Continuity test both forward and backward direction shows it's @ 0.127 V. This means that it's shorted, which seems strange, because it seemed fine. So i took it off circuit and found out it's working perfectly just like the other diodes (which i tested in circuit). I know these components ought to be tested out of circuit, but i was confused as to why this particular diode showed values so offset while all the other ones were on spot. Maybe someone knows ? (i think it doesn't matter now though)

    I cleaned the board, and the treadmill's belt thoroughly, although it wasn't in such a bad condition even after 3 years. I did not check the ceramic and tantalum caps, because it's very unlikely they're bad. I checked the NTC thermistor SCK 0512 which found to be working perfectly. I checked the CNR-14D471K varistor for shorts and in DMM continuity mode and found 0.57V across it both ways. I checked it for open circuits too, and it's @ ~820Ohms. So the varistor seems to be alright as well, as I don't have any specialized equipment to test it further. Hopefully it will be ok.

    The components i'm unsure off are the two white power resistors, which are apparently rated @ 10W & 30KJ. They display a black-orange like paste around their bases, which seems suspicious. They seem to be connected in parallel. I tested them and found them both to be @ 15KΩ (which to be limited knowledge seems quite a large amount for a power resistor?) Anyway, i hope someone can give me an opinion on that.

    At this point i don't know what other tests to perform on this. I'm troubleshooting it for about 2 days and i don't know what else to do. I ordered 2 of these MOSFET's and i'm waiting to find out what else might be the cause. I HAVE to fix my treadmill. I love it, i love running (i was always a runner) and i CANNOT do without it for much longer. I certainly cannot afford to buy another MCB, or treadmill now. Any help will be greatly appreciated. I have included multiple images of the motor, the board, the components etc. Thanks in advance.
    treadmill_lifegear_motor.jpg treadmill_MCB_1.JPG treadmill_MCB_2.JPG treadmill_MCB_3.JPG treadmill_MCB_4.JPG treadmill_MCB_5.JPG
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It sounds to me as though there may be an intermittent load problem, momentarily stalling the motor and causing an O/L.
    What if you try leave it running for some time with the belt off?
    This may pin it down if mechanical.
    Max.
     
  3. boydage

    Member

    Oct 7, 2016
    42
    6
    Hey in addition to Max I would check the motor as well. The bearings may be seizing or tightening once they become hot. Usually there is a noise but you never know. When I was reading I immediately thought mechanical as well. And bearings are as cheap as nuts.

    In fact I would be checking all bearings involved.

    Hope this might help
     
  4. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    I think the 'stuff' on the resistors is glue to support them and relieve the stress on their connections.
    D1 is next to R11, which I think is 10Ω. If the diode is connected is in parallel with that resistor then that would account for your readings.
     
    Dach likes this.
  5. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
    39
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    @AlbertHall yes. So the resistor is preventing the voltage change of the diode when testing it? I'm not sure why?

    @boydage I don't think the motor is a problem. I have checked the temperature of the motor and it really doesn't get very hot, especially in the temperatures i have put the treadmill now, i don't think so. About the bearings, yes that could be an issue, but to check that, i have to break apart the motor.. Anyway, i'll check that out too.

    @MaxHeadRoom why cause an open loop? Since it's clearly short circuiting the MOSFET and of course the fuse.. Can you elaborate more on this? So you are saying to run the motor with the load (the belt) off and see how it performs? Ok i will do that, i have ordered 2 identical MOSFET's and i should test this scenario in about a week (i'm very busy now with exam finals, but i had to get to solve this issue sooner rather than later).

    Thanks all.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Open Loop??
    The only way this would occur if there is a sensor somewhere after the motor itself.
    From my observations so far on T.M.'s, any feedback/sensor is usually on the motor itself.
    If there is something mechanical causing an unusually sudden loading of the motor, the current goes way up, so it would make sense to me to eliminate any mechanical problem after the motor is to run it with the belt off.
    Max.
     
  7. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
    39
    1
    @MaxHeadRoom you said "O/L" so i think this means Open Loop.

    You are right. That makes sense. Ok i will try that. In the meantime i took another photo of the motor just in case.

    Since you said sensor, i forgot to mention something. The first time this happened the fuse didn't blow. This happened the 2nd time. The first time, the treadmill's monitor displayed an "E1 error", which according to the manual, means that "The motor speed is faster than what the display shows". I knew this was probably a critical error, because it had never happened to me before and i was actually pushing the treadmill too hard at the time. But i kind of ignored the error, because i was in the middle of my sprinting session and i had to keep on going until i finish. So i just removed the power for like a couple of minutes, reinserted it again and started again. No error was showing then, so i fired it up. After a minute or so the fuse blew.

    I forgot to mention that. It may be helpful. Now you guys have the full story.

    treadmill_motor.jpg
     
    Last edited: Jan 20, 2017
  8. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    In the diode test setting the meter has a current source connected to its leads and it measures the voltage across the leads. That current will flow in R11 and if the resistor is a low value as in this case, the voltage drop across the resistor may be less than the diode forward voltage drop and so the diode never conducts. All the meter sees is the resistor.
     
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  9. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
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    Right! So from this test, we can also deduce the amount of current the MM passed through the resistor / diode. Which must have been ~ 0.127 V / 10 Ω ~ 13mA.
     
  10. drc_567

    Senior Member

    Dec 29, 2008
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    ... Just to mention ... Tantalum capacitors can be permanently damaged by reverse voltage ... even for an instant. ... Has to do with the thin metal film electrodes.
     
  11. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
    39
    1
    Hmm i don't think there would be a problem of reverse voltage in the MCB. You think it could slide from the motor? Do you think i should check them? It's unlikely though. They look fine..
     
  12. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
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    1
    Hi guys. I'm back. I have it all set up. I reassembled the PCB and disconnected the belt from the motor. I am about to test this and see if the motor is spinning properly, without any load. How much time should i give it? Anything else i should be careful? I don't want it to blow again. Thanks.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would think 10-15 minutes would be a sufficient test for anything to show up.
    Max.
     
  14. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
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    1
    Good news.

    First off, i could not completely remove all the load from the motor. The motor had to have the load of one roller (the upwards roller). I have uploaded a 26sec vid if you want to check it out here.

    This is because otherwise the error E2 would appear and shut down power. This is because the speed sensor would get no indication from the pulley where it's set at. So i had to include it.

    All went well though. I run it for about 18 minutes at varying speeds, usually fast speeds and it was doing just fine. So what now?
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That would seem to point to the motor and board working OK, if it acts up when connected then I would look for a mechanical problem.
    (O/L = Overload).
    Max.
     
  16. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
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    1
    I will test the treadmill myself tonight and see if it performs well.
     
  17. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
    39
    1
    I had to do complete maintenance on the treadmill. It was slippery, had to clean and stuff. Did nothing for 3 years now.

    Then i jumped on the treadmill and run for about a couple of minutes only. I noticed a lot of noise coming out of the motor. There may be a problem actually with it. What should i do to fix it? Clean it thoroughly? Take it apart? Grease the bearings? Any suggestions?
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It would be a place to start to ensure the motor is mechanically up to par, bearings could be a problem.
    Obviously it is something that is occurring under load.
    It was not electrical current caused noise possibly?
    Max.
     
  19. CobraL0rd

    Thread Starter Member

    Jan 18, 2017
    39
    1
    No, this noise is constant whether i am running on the treadmill, or the motor is running completely free of load. I did a test to run the motor alone on the treadmill and it makes the same squeaking noise. It's louder than what i remember. But from what I've seen it's the part that connects the motor with the pulley (which is kinda made of rubber, or pvc not sure) that makes the noise. It's that black part, you can see it on the image of the motor above.

    Should i take it out and inspect every bit of it?

    This is an expensive motor 4000RPM, 180V, 6.2A, 1.5HP cost over 100$.
     
    Last edited: Feb 22, 2017
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is known as a Poly-Vee timing belt.
    Check the belt for wear, and/or replace it, but I don't remember having seen that occur on those belts?
    Max.
     
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