I have a treadmill where the motor-speed controller is going bad.

I was wondering what people think i should look at first. The symptoms are as follows:

power/controller board successfully continues to work as motor-speed increases. the motor-speed controller board's "SRC TRIG" LED keeps "blinking" and the motor keeps turning UNTIL about "2mph" is on the display. the motor just stops and the blinking LED dies out. 3 wires connect from the power/controller board, so can i assume its a pwm sigmal to control the 4-wire DC motor?

the LED's on the power/controller board still "blink" the same and the display goes down to "0mph" because the magnetic-reed switch for speed is now longer getting input--if i turn motor manually the display shows an "mph" of me activating the magnetic-reed switch..

i'm attaching a pic of the board... the IC's are (2) LM324N's and there are three T220 "D1..3" and two T220 "Q1..2" attached to the huge-heatsink.

I'm assuming a resistor broke down and the LM324's are not comparing the speed of the motor correctly. could it possibly be a bad DC motor's speed-sensor? I thought of opening up the DC motor, but i can't imagine that sensor going bad.... am i wrong? the "current limit" LED never turns on

any help please.... ?

 

Although this is an older post, I have just repaired this motor controller and as part of the process had to reverse engineer the circuit board to be able to troubleshoot. I intend to use the treadmill motor to run my lathe. A couple of years ago I used another treadmill motor to upgrade my old Delta drill press. Since I spent the time generating the schematics of these two motor controllers, I thought it would be worthwhile to post them so others might use them to troubleshoot problems. I am quite confident that they are not 100 percent accurate but close enough to do some good.

 

Thanks for the hand drawn MC-60 schematic Trolly1. I have a fried SCR causing my treadmill to run full speed. I am replacing both with S4025L's that handle 5 more amps. Do you think I will have to modify the gate driver circuit? Reduce the 390 ohm resistors?

 

It was a great deal of help troubleshooting my board. It was not driving the motor at all. After testing and seeing all the signals, everything seemed to be working perfectly, but the scr's were not firing, so I assumed it was the opto-coupler. Turns out the "SCR FIRING" LED was not conducting enough current to turn the opto-coupler's LED ON, therefore not firing. Changing the LED fixed my problem! (The LED was actually lighting, for some reason not working the opto-coupler)

 

It's probably the optocoupler "ageing" and a typical symptom of an opto on the way out is the need to drive it with slightly higher currents.

It might have just been the LED, but I wouldn't be surprised if you soon have to change the opto too.

 

Thanks for the hand drawn MC-60 schematic Trolly1. I have a fried SCR causing my treadmill to run full speed. I am replacing both with S4025L's that handle 5 more amps. Do you think I will have to modify the gate driver circuit? Reduce the 390 ohm resistors?

I haven't been logged on for a while. I would guess that you would not have to modify the gate driver circuit. You could compare the gate triggering requirements of your SCR with those of the original.

 

It's probably the optocoupler "ageing" and a typical symptom of an opto on the way out is the need to drive it with slightly higher currents.

It might have just been the LED, but I wouldn't be surprised if you soon have to change the opto too.

Those are exactly the problems that I found when I repaired my MC-60. Had to replace the LED and the opto-triac.

 

My Horizon T30 treadmill has been through four motor control boards and each time it blows the Fast Recovery Diode that is in series to the motor. Last time, I replace it with a much higher-rated one but the motor still doesn't move. Any ideas there?

Thanks!

 

Ive struggled with a MC 60 that the motor wont run and the SCR Trig LED wont light. Outputs,caps,all solid state items check good.Ive replaced both LM324s, MC3052 and the SCRs went and replaced all caps with no luck. I dont like shotgunning a repair but was stumped. I swiped a LED from another controller and still no luck. What am I missing. How do you test a LED and what is a sutable replacement?

 

If you have access to an oscilloscope then you can trace the SCR trigger pulses. Testing a LED in-circuit may be tricky. You could lift the non-grounded lead and apply voltage thru a resistor. Basically the circuit is applying 12 volts thru a 510 ohm resistor so you could clip in a similar sized resistor directly from the 12 volt supply and see if the LED lights. Check to make sure the 12 volt is proper with a meter. Alternatively you could temporarily short out the SCR Trig LED and see if the motor works. It is not essential to make the SCRs fire but if open they won't.

 

Just started this repair project.
My treadmill simply doesn't get power to the belt motor.
Power is there. SCR LED not firing.

Thanks for the schematics!

 

hello,
thanks for mc-60 schematic. I have also a problem with my treadmill...The speed of the motor seems good, but when i step on the speed decrease and the motor stop. an idea of the reason?
Thanks.

 

Thanks for the schematics! My controller is dead. No LEDs light. I replaced D1, D2, D12, Q2, and Q3. Still no LEDs. I checked for voltage across C5 and only see about 0.6V, not 12V. What is the symptom if the optocoupler (MOC3052) is blown? Any other suggestions? (I don't have a scope to debug...)

 

Cneck the resistance across the H and L terminals. Lift one end of D-10 the 12v zener right next to C-10. If the short is removed theres the problem. Otherwise its a pains taking task to locate the shorted compponent. There are several small caps and ICs that short on occasion

 

Great thread guys. I am having eratic speed issues. When I start the treadmill it starts at a fixed speed and then just slows down. I can never get it to speed up.
I have gone through all the steps described on the <SNIP> site.
The magnetic Sensor is Okay.
There is no short on the Motor
The PWM LED is blinking.

Any input is appreciated.

The schematic would be of great help. Kudos to trolley1.

 

Have you searched for a schematic or repair manual based on whatever model your treadmill is?

 

tvmanjon,

Thanks for the suggestions! I really appreciate the help.

The impedance across the H & L contacts is 41.4 ohms. (What should I expect?)
Removing D10 (and D9) have no affect on impedance.
LEDs all seem to check out
Diodes all seem to check out
Caps all look good from an impedance perspective (nothing shorted...)

Any other hints or suggestions?????

Jaime

 

All the leds' on my board light up good. I desoldered the MOC3052 and tested whether the TRiAC could turn on an AC load and it did not. Ive just ordered some MOC3052's. Hopefully that is it.

 

When I connect a Ohm meter to HLW terminals on the power board, IT reads 5K, upon increasing/reducing the speed, the resistance does not change. Any thoughts

 

why in the world are you people continuing in forgotten threads, for Pete's sake open a new thread in the appropriate forum.