Treadmill goes high speed then blows the fuse

Thread Starter

yogi799

Joined Nov 25, 2015
25
Last time treadmill ran, my son says it was fine, then all of the sudden very high speed and then stopped. We could smell something burnt.

I take the cover off and find good connections to the MCB, but there is a blown fuse.

I replaced the fuse, the lights on the MCB turn on when power is plugged in and the electronic displays as well.

Turn the treadmill to START and the motor goes very fast and within .5 seconds the fuse is blown again.

Tried the motor on a 12V car battery - works no problem, turns slowly without noises or sparks.

Also, when I replace the fuse and plug in to power, a yellow LED on the MCB lights up. That LED has "SPEED" printed next to it.

I am VERY new to treadmills, can you treat me like a 5 year old?

What is wrong and can I fix/replace anything?

It is Free Spirit treadmill 302001, I believe. I can upload pictures of the board if needed. Much appreciated.
(I know there are similar threads to this one, but I wanted to describe my particular case and the treadmill model)
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Thanks Max, can you guide me a bit closer? I see something at the back, but is there a particular part, with a name, that I should look for? Proprietary or generally available? Simple replacement?
 

MaxHeadRoom

Joined Jul 18, 2013
19,695
You would need to remove the heat sink clamp on the top R.H. side to see the vertically mounted components underneath, they will have a part No. on them.
Search the part No's at Digikey etc.
Max.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
OK, thanks a Million Max. Will do so.

(un)Related question... Say, worst case scenario, I cannot get the part or whatever. Could I make my own speed controller connected directly to the motor and mounted near the controls up on the top, just so the kids can still use it? The motor works fine... if I could just control its speed... Is it safe to do that? What do you think (again, that'd be my plan B).
 

MaxHeadRoom

Joined Jul 18, 2013
19,695
You can get controllers such as KB or make your own, the problem is that most have a speed sensor on the motor to control rpm.
Also the commercial controllers are made so that the speed control has to be at zero before you can increase the speed, this is so someone standing on the T.M. does not have full rpm right away.
I would take a crack at fixing that one first, do you have a meter etc?
Max.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
I have access to the multimeter (if this is what you meant).
Here is the pic again, are we talking about replacing these two transistors?
 

MaxHeadRoom

Joined Jul 18, 2013
19,695
Yes, I would test them with a meter out of circuit first.
The fact it powers up OK I don't think it is the DC bridge BRT1, the other reason for it to take off is if it has a optical tach and that is defective.
Max.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
OK, thanks again Max. Glad to have an expert here. I know you've helped others before with similar issues (I've seen some threads) but each case is a bit different (and diff. equipment). I'd get drunk (and send you a 12-pack) if I could fix it myself. Probably a long shot, but who knows - if I could actually find these transistors online for not too much dough... Maybe...? (I've never done electronic repairs before... I've literally soldered one tiny thing in my entire life. I presume these two transistors need to be cut off with side-cutters and soldered back, eh?)
 

MaxHeadRoom

Joined Jul 18, 2013
19,695
You would need to carefully unsolder the existing leads, if you cut them and the device is OK then you replace them unnecessarily.
Digikey should have the new replacements, what country are you in?
At 120vac in I assume it is N.A.?
Max.
 

GopherT

Joined Nov 23, 2012
8,012
Yes, I would test them with a meter out of circuit first.
The fact it powers up OK I don't think it is the DC bridge BRT1, the other reason for it to take off is if it has a optical tach and that is defective.
Max.
OK, thanks again Max. Glad to have an expert here. I know you've helped others before with similar issues (I've seen some threads) but each case is a bit different (and diff. equipment). I'd get drunk (and send you a 12-pack) if I could fix it myself. Probably a long shot, but who knows - if I could actually find these transistors online for not too much dough... Maybe...? (I've never done electronic repairs before... I've literally soldered one tiny thing in my entire life. I presume these two transistors need to be cut off with side-cutters and soldered back, eh?)
Stop!

I think max nailed it - optical tachometer. Also, look at all the cat hair / dust on the board. It is very possible that the optical tachometer is just dirty and full of cat hair and lint.

Clean it up with a can of dust off or vacuum cleaner. Then try again.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Stop!

I think max nailed it - optical tachometer. Also, look at all the cat hair / dust on the board. It is very possible that the optical tachometer is just dirty and full of cat hair and lint.

Clean it up with a can of dust off or vacuum cleaner. Then try again.

Where is the opt tach in my pictures?
 

GopherT

Joined Nov 23, 2012
8,012
Where is the opt tach in my pictures?

There is usually some type of feedback system to control motor speed. Look for some wires going to some type of axle or pulley. Maybe even the back of the motor. Essentially a toothed wheel or perforated disk and an infra red light and detector to detect pulses of light as the motor turns. If the dirt is blocking the sensor, then the motor thinks it is stopped and more current applied (or higher duty cycle). I am not sure where it might be on your treadmill.
 

Thread Starter

yogi799

Joined Nov 25, 2015
25
Are we talking about this part (sensor near the wheel?). I don't know about that... the tread goes really fast immediately after I press START... as if it was given the highest power from the get-go. How would I test it?



Also, here is one of the transistors.

 

GopherT

Joined Nov 23, 2012
8,012
Are we talking about this part (sensor near the wheel?). I don't know about that... the tread goes really fast immediately after I press START... as if it was given the highest power from the get-go. How would I test it?



Also, here is one of the transistors.

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.
 
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