Treadmill goes high speed then blows the fuse

spinnaker

Joined Oct 29, 2009
7,837
That would be it. Can you tell what is on the end of the sensor (the tube with the wires sticking out)? Does it look like a lens or is it opaque?

And are those fuzz balls in front of the sensor? If so you should blow that dust free.
 

spinnaker

Joined Oct 29, 2009
7,837
That is exactly the type of sensor I was talking about. Now, there should be the light source on the other side of that pulley. It looks like that area is full of cat hair. Take off the sensor, clean it out. Make sure the cat hair in the pulley is cleaned out as well - so the sensor' slight is not blocked. Then try to find the second half of the sensor on the other side of that pulley and clean that too.

Finally, make sure they are well aligned - pointing directly through each other.
It almost looks like it could be magnetic to me. Is that possible? See the disk on the wheel? Looks like a metal plate to me.
 

GopherT

Joined Nov 23, 2012
8,012
It almost looks like it could be magnetic to me. Is that possible? See the disk on the wheel? Looks like a metal plate to me.
Yes, you are right!

It looks like the sensor got bumped. It should be positioned right in front of that little metal "coin" on the wheel. So it can detect when that coin passes.
 

MaxHeadRoom

Joined Jul 18, 2013
19,968
That could also be a prox switch if there is no aperture on the wheel.
Looks like the bracket got bumped, only held on with one screw?
Those IRFP250 Mosfets are available at Digikey.
Max.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Are you guys kidding me?? Could that be it??? Yes, the sensor is clearly at an angle... I saw that but thought that was intentional... but yes, there is a plate on the pulley... Geez... I will try now...
 

spinnaker

Joined Oct 29, 2009
7,837
One way to test if it is magnetic for for is to place a paper clip on it. It should stick to the "coin". But I suppose it could stick to the sensor but more than likely the "coin". Remember to remove the paper clip if it sticks.


If it is a magnet, disconnect power to the treadmill. Trace the wire to the board and disconnect it. Place an ohmmeter or test light between the two contacts. You should see the contact opening and closing, as indicated by the light or meter, as you spin the wheel with your hand.

If it is magnetic it will be less likely fuzz will be an issue but it won't hurt to clean up that area. The test will confirm the sensor is at least working.


Those mosfets don't look healthy to me. Anyone else?
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
No, it was not the sensor, I think. I aligned it back, the yellow light SPEED blinks when the sensor meets the plate (as it was from the start, I now recall). I turned it on, and BAM, same think 0.5 second following the START button, the tread moves fast for a blink of an eye and the thing blows. So it must be the transistor(s)?
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
OK, I may have found it... I touched one transistor and it fell off the board! I did remove & reinstall the heatsink plate to test the board with the speed sensor realigned, but I don't think that would have broken it off - i was very gentle when tightening the screws. Is it possible that it simply got detached (while appearing in place) and hence the high speed/high power effect? What do you think? See the pic with the broken off transistor next to its spot.

 

MaxHeadRoom

Joined Jul 18, 2013
19,968
That is a high speed diode, I would not have thought that would have caused it, but it may have broken and then cooked the Mosfet?
It needs replacing now anyway!!
Farnell is usually costlier than Digikey in Canada, I have next day air for $8.00 no duty or brokerage.
Max.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
So likely both the transistor and the diode? I have someone who can possibly test the transistor for me tonight.

Question : should we try soldering back the diode first? Or do you think the transistor has to be dead too?
 

spinnaker

Joined Oct 29, 2009
7,837
So likely both the transistor and the diode? I have someone who can possibly test the transistor for me tonight.

Question : should we try soldering back the diode first? Or do you think the transistor has to be dead too?
That lead looks awfully short. I don't see how you will be able to solder it properly. Remember that it needs to be mounted in such a way that is affixed to the heat sink. And you will need new heat sink compound anyway.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Get them to test the Mosfet also for shorts etc.
Max.
You guys were bang on. Just bang on. My friend checked the transistor and it's blown. The diode is fine. Transistor is on order, the diode will (hopefully) be reused. He fixes TV's so hopefully soldering will pose no challenge, he didn't seem concerned. This forum is unbelievable... Well I mean you guys.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
UPDATE:

new transistor was soldered on. so was the diode that fell off. both (and everything else) checked with a multimeter.

installed the MCB into the treadmill and get something else now. the unit powers on and when I click START, the tread does not move. the incline option works, all the electronic displays and timers do. but no movement.

hooked up the motor to 12v battery and it moves just fine.

what could it be now?

Mind you - before, the motor was getting TOO much power, ran full speed and blew the fuse every time. now, everything works, but the motor gets no power at all. Is it possible that something else was broken on the board when the transistor and the diode were being soldered back on?

video

 
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