A noisy treadmill

[zap]

I picked up a free treadmill from a friend last weekend.  Proform 755cs... seems like a nice enough unit, incline, 6 pre programmed routines, etc. etc, etc...
I was told my friend started smelling "smoke" and decided to get rid of it.  Getting it home, plugging it in and running the belt... it was noisy.  Taking the cover off, nothing inside looked "bad".  I loosened the drive belt and discovered the noise was coming from the motor but... only when under a load... it was silent when spinning down so I was pretty sure it wasn't bearings.
I re tightened the drive belt and hooked the motor up to an SLA and sure enough, operation was as quite as could be on pure DC.

This treadmill uses the venerable mc60 motor controller.  Upon closer inspection of the controller I noticed one resistor that appeared to be clipped so I bridged it back with solder.  That didn't help the noise much and now the machine showed strange behaviors with regard to speed.
A search online showed that different resistors on the board can be clipped to allow the board to function correctly for different treadmills.  I broke the connection on the resistor and the treadmills operation fell back to normal.

What now???

This particular treadmill uses a choke inline with the walking belt's motor.

I'm fairly certain the noise is coming from a dirty PWM signal and it's evident the choke has seen some heat somewhere in the past.

I don't want to buy another controller and I really don't want to try and debug the existing controller.

Should I try winding another choke or just turn the music up louder to drowned out the chatter coming from the motor because of dirty PWM coming from the mc60?

[joestue]

chokes don't go bad.

replace the electrolytic capacitors (or add more) that filter the incoming DC.
those caps have to take the full RMS ripple current. you could also add a *few* uf across the motor. But without an oscope and a current transformer you should be careful with that. 

[ghurd]

I don't know anything about that controller....

I'd make sure the choke is not smoked.  Somehow.
WAG, Maybe try it at a few speeds and see if it gets warm???
A lot of them kind of look smoked from the color of the varnish.

I'd look at the caps.  Bulged tops, drain the charge and check the DC resistance, etc.

Might try a cap after the choke?  (that's what I'd try)

Or make the drive motor into a windmill and the incline motor into a solar tracker!
G-

[zap]

I figured the first thing I'd check is the choke.  I built one of the inductance testing kits from MPJA so I'll have to dig that out.
I'd like to try a cap after the choke but I'll need a starting place for the value.

Or make the drive motor into a windmill and the incline motor into a solar tracker!
G-

Funny how fate works sometimes.
I put the feelers out to friends for a treadmill about a year ago because my girlfriend wanted one.  When she decided to become an 'ex' all of my friends knew it and I figured there was no need to retract the "feelers".
When I was offered this one I figured on gutting it since my only other treadmill motor is now part of the bike generator system.
Once I got it home I realized it's a pretty nice unit and tearing into it for parts just seemed wrong.  I'm not really sure I'd ever use the thing once I get it quieted but you never know.

I was headed to the store a day or two after I got the treadmill and decided to stop by "The world's best dumpster".  I visit it way more often during summer months when I'm riding the bike but only once every month or less once I'm not riding.


I looked inside and spotted something...


Guess I don't really need to gut the good one...

All but one work and that one still puts out a voltage but no amperage and it won't spin with voltage applied... I'm thinking commutator or toasted windings.  I'll have to dig in to it.

[RP]

The diagram indicates it's an SCR controller meaning it uses SCRs to convert AC into pulsing half wave rectified DC.  I doubt there's any (significant) capacitors across the motor power leads because it would take an enormous amount of capacitance to carry the current needed to make a difference.  The inline choke is used instead and I agree they rarely fail.

I suspect the most likely culprit is the SCR itself.  Take a look on the controller board for a 3-legged device that looks likes a big power transistor.

[12AX7]

chokes don't go bad.

replace the electrolytic capacitors (or add more) that filter the incoming DC.
those caps have to take the full RMS ripple current. you could also add a *few* uf across the motor. But without an oscope and a current transformer you should be careful with that.  

I've an old Dynaco MK3 that has an open choke.  

and no,  it's not a motor controller.  

Years ago while I was working maintenance I was told to replace a conveyor motor due to a bad bearing.
I used a stethoscope to listen to the bearings,  they were "singing"  but so was everything else.   Replaced the AC drive and no more noise.    I myself did not believe that the drive was causing the problem,  but it took 5 min. to replace the drive and would have taken me 5 hours to replace the motor. 

I wish I had a scope available,  would have liked to compare the output of the two drives.

There was no noticeable performance differences between the two drives.   Both had the same range of speed control and both had the same amount of torque.

[zap]

I've found a lot of info on the mc60.  This page and some of the other pages at another forum has some good pictures of the beast:
http://forum.allaboutcircuits.com/showthread.php?t=42116

I've already tried another motor, not installed but using the controller and it made the same noise.

I've also bypassed the choke and it made no discernible difference in noise.
I think I'll dig out the impedance tester... somewhere in all my surfing I saw a rating somewhere on how many mH it should be.  I think it was 500mH.

[zap]

UPDATE

I messed around with the inductance checker but was getting funky readings.  The readings I was seeing seemed to say the choke was bad.

I found a choke of similar size on an old microwave transformer and the treadmill wasn't silent but tons quieter.

I walked on it at various speeds... 1 mile, maybe 15 minutes and the new choke was pretty warm.  I didn't measure it but probably 95-100­°F.
I wasn't putting much strain on it so something in the controller is probably bad.