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.
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.