Treadmill goes high speed then blows the fuse

MaxHeadRoom

Joined Jul 18, 2013
19,968
Measure for DC voltage from a DC common point or ground plane on the board to the drain side of the Mosfet or from Source to Drain and measure the power DC, it will be somewhere common to the terminals on the large capacitor.
Max.
 

kubeek

Joined Sep 20, 2005
5,674
The blown mosfet probably took with itself the drive circuitry. If you are lucky it´s just the gate resistor if there is one. What marking is on that chip right next to the mosfet?
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
This one? Here...

I'll check the voltages with my friend today or tomorrow.

My thing is... the motor used to get power (too much of it), now it doesn't (but everything else works fine). I'm curious if something was messed up during the repair - OR - this turn of events makes perfect sense to you guys.

BTW, the two white pieces near the bottom get very warm when the treadmill is on START. I suppose that's perfectly fine..?

 

kubeek

Joined Sep 20, 2005
5,674
That is because mostfets generally burn to a crisp and all three leads become connected together. That way the mosfet applied full power to the motor, and full power to the driver output which generally is not good. Now the mosfet is not getting any signal so it is off and nothing happens. That chip is a fairly common, so you should easily be able to replace it, and I suggest you use a socket just in case so that you don´t have to resolder it ever again.
 

kubeek

Joined Sep 20, 2005
5,674
Do you have an oscilloscope? Or your friend, you said he fixes TVs so he might be able to help you a bit more.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
**** UPDATE - PROBLEM SOLVED ****

Thanks again guys. The treadmill works like new (knock on wood). Just gotta lube it now, so it's still on hold until tomorrow. And get a heavy duty extension cord just in case (was using a middle duty).

So my friend checked the board again and could not find anything on the outside using the multimeter. We suspected some burned chip which would basically be the end of it (plan B would have kicked in - the motor operated on a dimmer switch). Then he remembered something that he did to the board when soldering my transistor. He thought there was some small "jumper" at the bottom of the board that looked suspicious to him and which supposedly broke off when he was working on the transistor. So he got one from another board and soldered it back on (looked like a tiny resistor). I don't know where he got that whole idea from (maybe he was just drunk LOL) but that's what was screwing it all up! He cut it off, I reinstalled the board.... and the motor powers on like new. Everything works fine. WHEW....

So, in case you're like me and you like to get to the bottom of issues to understand the root cause... I think in my case, the diode broke off due to the constant impacts and vibrations which then blew the transistor. The 15AMP 250V fuse saved all the electronics and the motor (nice design!). The diode was salvageable but the transistor (JUST LIKE YOU GUYS SAID) was not. So it was potentially a $4 repair... something that "a certified professional" would have charged me $200 for or $200 (labour) + $200 (for a new board?). Insanity... It cost me $13 because of the shipping charge.

Thanks again. You guys rock and you've saved me a tonne of cash and stress. This was the first purchase of my 13 and 11 yr olds for their own money, it'd be a shame to have to ditch it over a $4 transistor. I've never owned a treadmill before or done anything with any electronics (I'm more on the software side). Now I just have to lube the belt and hope it lasts my kids for a few years. MANY thanks.
 

GopherT

Joined Nov 23, 2012
8,012
**** UPDATE - PROBLEM SOLVED ****

Thanks again guys. The treadmill works like new (knock on wood). Just gotta lube it now, so it's still on hold until tomorrow. And get a heavy duty extension cord just in case (was using a middle duty).

So my friend checked the board again and could not find anything on the outside using the multimeter. We suspected some burned chip which would basically be the end of it (plan B would have kicked in - the motor operated on a dimmer switch). Then he remembered something that he did to the board when soldering my transistor. He thought there was some small "jumper" at the bottom of the board that looked suspicious to him and which supposedly broke off when he was working on the transistor. So he got one from another board and soldered it back on (looked like a tiny resistor). I don't know where he got that whole idea from (maybe he was just drunk LOL) but that's what was screwing it all up! He cut it off, I reinstalled the board.... and the motor powers on like new. Everything works fine. WHEW....

So, in case you're like me and you like to get to the bottom of issues to understand the root cause... I think in my case, the diode broke off due to the constant impacts and vibrations which then blew the transistor. The 15AMP 250V fuse saved all the electronics and the motor (nice design!). The diode was salvageable but the transistor (JUST LIKE YOU GUYS SAID) was not. So it was potentially a $4 repair... something that "a certified professional" would have charged me $200 for or $200 (labour) + $200 (for a new board?). Insanity... It cost me $13 because of the shipping charge.

Thanks again. You guys rock and you've saved me a tonne of cash and stress. This was the first purchase of my 13 and 11 yr olds for their own money, it'd be a shame to have to ditch it over a $4 transistor. I've never owned a treadmill before or done anything with any electronics (I'm more on the software side). Now I just have to lube the belt and hope it lasts my kids for a few years. MANY thanks.
Ok, it did cost $13 but it sounds like you got way more than $13 in satisfaction out of thus project! Thanks for keeping that heap out of the landfill!
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Oh hell yeah... Nothing feels better than a) not getting ripped off / having to throw away an otherwise perfect machine, b) be able to fix something I had absolutely no idea about. You guys made it happen for me. And I felt bad for the kids too, so that's an added bonus.

The kids bought this thing for $120 only 10 days ago..., pretty cheap, but that's why even if I could buy a new MCB for $100 on ebay (they are nowhere to be found due to their age, and other boards go for $200), it just wouldn't feel right. Fixing it for $13 was just perfect. Still can't believe it. Well, the fuses were $4, $3 for my friend for soldering (pretty good rate ain't it), so my total cost was closer to $20 :)
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Hey guys... not to resurrect my thread from a year ago... But the treadmill worked fine for 2 months and blew another fuse in the very same way it broke all the previous ones (instant high speed on the tread, burnt smell and blown fuse). I suspect the MOSFET is gone again.. Now I am suspecting there is something else going on that destroys the mosfets.... I may just buy a load of them and learn how to solder myself. Or just sell the darn thing.. If there are any ideas... let me know... But I am not too optimistic.
 

MaxHeadRoom

Joined Jul 18, 2013
19,968
You could try the IRFP260 instead, quite a bit higher current rating.
Is everything seem free mechanically? Not considerable friction between motor and belt?
Max.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Yeah, it seemed to run OK. Kids had it at a very high speed many a time. I even put more silicone to lube it well and all....

Hmm... do you think it's safe to go with 260? Ie. will it still prevent a fire etc in case there is something else going on?
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Wait.. someone up in the thread said "to remember heatsink compound". Does he mean thermal paste like what we use on CPUs? I know there was none on the back of the mosfets. Should I apply some? Maybe it's just overheating??
 

MaxHeadRoom

Joined Jul 18, 2013
19,968
Thermal paste helps, but the 260 is rated a little higher, I am guessing the fuse blows when the irf250 current is exceeded, the fuse will still blow if the current is excessive.
Max.
 

MrSoftware

Joined Oct 29, 2013
1,674
If there's any available power for a small fan, then you could also make sure a fan is blowing in the heat sink for the transistors. Maybe that would help?
 
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