MC-60 treadmill controller problem

Discussion in 'Technical Repair' started by chucketn, Sep 26, 2016.

  1. chucketn

    Thread Starter New Member

    Jan 22, 2012
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    I have 3 treadmill controllers, all various configurations of the infamous MC-60. Two are working fine, one has a problem. on the problem controller, a revision K, the motor will start and run if and only if the speed pot (5 k ohm linear) is turned to minimum and slowly back up. This is o.k. as it's a safety feature. The problem appears as the pot is turned to just before max speed. The motor stops, but will not restart until speed pot is returned to zero again The Current limit led does not come on when the motor cuts out, but the scr trigger led does go out. I was an Air Force avionics tech 45 years ago, but still remember some of the basics.
    I cannot find troubleshooting info on this controller. Can someone explain what is happening, and what is/may be bad, and how to check it. I only have a multimeter for testing.?

    Chuck
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What happens to the SCR trigger LED if you disconnect the motor?
    Max.
     
  3. chucketn

    Thread Starter New Member

    Jan 22, 2012
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    I disconnected the motor and operated the control. Same results. No overcurrent lite,
    12v, speed control, and scr trikker lite as speed pot is turned up. scr trigger goes out just before pot maxes out.
    Chuck
     
    Last edited: Sep 26, 2016
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Disconnect the motor before powering. Or place a lamp in place of the motor.
    If it does not have sensor on the armature.
    Max.
     
  5. chucketn

    Thread Starter New Member

    Jan 22, 2012
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    I did as you said. No sensor connected. Results as above.
    I have a wall switch in a metal outlet box as a power switch. The setup was used on my sand muller with a different MC-60. I disconnected it and brought it to the shop to troubleshoot the mal-acting one.


    Chuck
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Did you monitor the pot slider voltage input terminal from common to slider and see if the voltage remains.
    Max.
     
  7. chucketn

    Thread Starter New Member

    Jan 22, 2012
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    That seems to be the problem. The pot voltage goes to zero when the motor quits and the scr trigger light goes out. 12v light stays on.
    Oh, and thanks Max for your help...
    What would cause that?

    Chuck
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    First check the pot continuity etc!
    Place a 9v battery across the outer ends and measure between slider and one end.
    Max.
     
  9. chucketn

    Thread Starter New Member

    Jan 22, 2012
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    That will have to wait until tomorrow. Don't have a 9v battery. Any other suggestions?
    I don't have a spare pot either. The other controller in use has the pot mounted inside the equipment and would be a big hassle to remove. Nearest radio shack is 40 min away(one way). So looks like a road trip tomorrow. Any other possibilities?
    BTW, pot used in the test works fine on another MC-60 setup. I think the problem is still with this particular controller.

    Chuck
     
  10. MaxHeadRoom

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    I will check the schematic and see if I spot something.
    Max.
     
  11. MaxHeadRoom

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    Do you have the schematic in order to trouble shoot it? I have the reverse engineered one.
    The opto U3 has often been a source of failure.
    Max.
     
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Here are two tidbits I found on the internet..... I got them for reference when seeing the MC motor controller in the threads.
     
  13. MaxHeadRoom

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    Yeah.. That is the two I have and posted in a few forums.
    Max.
     
  14. chucketn

    Thread Starter New Member

    Jan 22, 2012
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    Do you think the opto-isolator could be the cause in this case? Do you have a spec on it so I can order a replacement?

    Chuck
     
  15. MaxHeadRoom

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    I don't have the original Part No.
    The Fairchild line is one source MOC301/302/305 series of random phase opto couplers.
    Max..
     
  16. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    @MaxHeadRoom you answered my question I was going to post today. I'll finish up on the simulation later.
     
  17. MaxHeadRoom

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  18. MaxHeadRoom

    Expert

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    A little more data.
    Max.
     
  19. chucketn

    Thread Starter New Member

    Jan 22, 2012
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    I'm too far from experience as to which one too choose. Can you recommend one? Mouser seems to have all three.

    Chuck
     
  20. MaxHeadRoom

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    MOC3052 seems to be the one most used.
    Max.
     
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