MC-60 treadmill controller problem

Thread Starter

chucketn

Joined Jan 22, 2012
22
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
 

Thread Starter

chucketn

Joined Jan 22, 2012
22
What happens to the SCR trigger LED if you disconnect the motor?
Max.
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:

Thread Starter

chucketn

Joined Jan 22, 2012
22
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
 

Thread Starter

chucketn

Joined Jan 22, 2012
22
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
 

Thread Starter

chucketn

Joined Jan 22, 2012
22
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
 

MaxHeadRoom

Joined Jul 18, 2013
23,635
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.
 

Thread Starter

chucketn

Joined Jan 22, 2012
22
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
 
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