MC-60 from treadmill, broken resistors

MaxHeadRoom

Joined Jul 18, 2013
21,402
What you most likely could do is place a lamp across the motor terminals, and jumper the triac output of the the MOC3052.
The bridge should turn full on, use suitable fusing.
Max.
 

Thread Starter

DomMc

Joined Nov 9, 2014
28
What you most likely could do is place a lamp across the motor terminals, and jumper the triac output of the the MOC3052.
The bridge should turn full on, use suitable fusing.
Max.
Presumably that is to test if the DC motor itself is dead/functioning?
(I tested the motor with a cordless screwdriver battery and it seems good)

To jumper the triac, do I connect pins 4 and 6?

moc3052-jumped.png
 

Thread Starter

DomMc

Joined Nov 9, 2014
28
One other observation (and thanks for the docs Max).
According to the attaachment: D6- Labeled SCR. Indicates that the SCR is triggering on the controller. If this light is out, no voltage will be sent to the
motor. Note that this LED will vary in brightness, depending on the speed setting.

On my board its either off or on.. I didn't notice any graduation in the strength of the LED light.
 

MaxHeadRoom

Joined Jul 18, 2013
21,402
Yes, 4&6 should turn the bridge full on.
If the LED is on at all the output should be on.
Check all the low voltage DC points as well.
Max.
 

Thread Starter

DomMc

Joined Nov 9, 2014
28
Yes, 4&6 should turn the bridge full on.
If the LED is on at all the output should be on.
Check all the low voltage DC points as well.
Max.
Ok, so the SCR Trig LED is connected to pin 2 of the MOC3052 ?
or do you think its in parallel on pin 6 ?
(if its pin 6 then probably the triac is working)

This is my last hope really.
If I cant conclusively identify that chip as the culprit I'll likely admit defeat and head to ebay for a replacement. :(

p.s Thanks again for all your help to date!
 

Thread Starter

DomMc

Joined Nov 9, 2014
28
Some further troubleshooting tonight.
I set about finding the 390 ohm resistors which are in line with the MOC3052.
(Orange, white, brown, xxxx - right?)

Pulled them and checked with a multimeter and both seemed bang on. 0.387 K ohm.

Then decided to pull out R28 which is on the main loop for the bridge/rectifier.
It does not read well on the multimeter. Should be 0.01 Ohm.
Shows as zero.

Although I am using the worlds cheapest multimeter.
Howver, the continuity test beeps - so does that indicate that the resistor may be good and that my meter is rubbish?
 

wayneh

Joined Sep 9, 2010
16,399
My meter can't read anywhere near enough precision to judge that. Heck, just the leads themselves would have more resistance.

I'd put a known current across it and measure the mV voltage drop. If you have another cheap meter, you can put it in series to measure the current while you use the 2nd meter to measure the mV drop.

Do you have the power rating for that resistor? The more amps you can put thru it, the greater the mV drop, but you don't want to roast it.
 

wayneh

Joined Sep 9, 2010
16,399
OK, so 10A would be 1W - well under the 3W rating - and would give a drop of 100mV. More than enough for an accurate measurement. If you have a spare headlight in the garage, they draw ~4A from a 12V battery. Again, more than enough for a measurement.

FWIW, I think it would be unlikely for a resistor to fail to a short. They tend to blow like a fuse and go open. Maybe the resistance could go high without going open, but I can't say I've ever seen that.
 

Thread Starter

DomMc

Joined Nov 9, 2014
28
Great.. thanks for the insight.!!
It is my secondary line of investigation.
I'm still hoping its a case that the MOC3052 is dead - and I can simply replace it.
I've soldered a jumper cable across that component so can hopefully check tomorrow if the motor starts.
 

MaxHeadRoom

Joined Jul 18, 2013
21,402
I would use the lamp in place of the motor, shorting the MOC will turn the bridge full on.
The resistor is in the current detect circuit.
Max.
 

Thread Starter

DomMc

Joined Nov 9, 2014
28
I would use the lamp in place of the motor, shorting the MOC will turn the bridge full on.
The resistor is in the current detect circuit.
Max.
I can do that.. you mentioned before about ensuring the correct fuse. Can you suggest a good test setup?
 

MaxHeadRoom

Joined Jul 18, 2013
21,402
If you have something like a pig tail inline fuse holder for a 1" glass fuse etc is ideal in line with the 120v to the TM circuit or rig up what ever type of fuse holder you may have on hand.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
21,402
No, treadmills typically have a slow start built in to speed controller when initially switched on.
IOW, there is never full motor voltage from at switch on.
Max.
 

IamJatinah

Joined Oct 22, 2014
122
Sorry to disagree, but in it's stand alone design, the MC-60 wouldn't drive more than a few dozen Amps and for only a short time until the current capability would be distinguished completely. If you look into the "system" electronics associated with this control board, you will find a 20# say 30Amp choke or Inductor in series with the MC-60 output to the DC motor. This added inductor is critical to this design, or I am afraid you would be driving very heavy current in it's stand alone state. Sure, SCR or Thyristor rectification can work nicely, but you can never drive more than a devices ratings, and never forget the intricate importance of XL / XC and the rules of motor operations. To overcome "Inertia" alone, the MC-60 would be hard pressed to deliver enough gumption to spin a motor in it's stand alone configuration, and at extreme's, overcoming inertia can take up to 600x the normal current loading for an extremely short time. We also haven't addressed the AC components residing on these drive lines without the added inductance.
 

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