OT - long-arm sewing machine has intermittant stoppages

[Tony Ennis]

Ok, the wife has a long-arm quilting machine. The machine is basically a large-throated sewing machine meant to sew quilt tops to the backs with a layer of padding sandwiched between. Fairly powerful machine.

She's starting to have what we think is an electrical issue.

The machine includes incandescent lights, a motor, and some solid-state hardware of course.

The repair company is in Northern Ohio though she prefers to deal with the Michigan repair facility. To get the machine to Michigan (or Ohio for that matter) will cost a lot of money and time whether we drive or ship it.

The machine has worked flawlessly for years.

The symptom that started last week was that after a few minutes of usage, the motor would stall or stop. Cycling the power on the machine would allow the machine to continue for a few more minutes, then it would happen again. There's a start-stop switch on the operator's grip, but this would not bring the machine back - only a real power cycle would do it.

This intermittency seems to be heat related, though I could not find anything hot on the machine. That is, first thing in the morning, it would run for a while, then the failures would begin, and become more and more frequent.

Yesterday as per the repair shop (via phone support) I replaced a transformer. The new one is rated about 2.5 times the power of the old one. Since the replacement, the machine has halted once, after a much longer time than has been the norm lately.

But it still halted. So while the transformer may have played a role, it isn't the culprit, or it created a secondary problem.

Is the motor failing? It's a 90v dc model. Could the previous under-sized transformer have damaged the motor, and now the new transformer is doing what it should, but it's too late?

Of course the motor speed is controlled by a computer circuit, so if that circuit is failing all bets are off.

An incandescent light electrically attached to machine does not flicker when this happens.

What causes a DC motor to stop?

[Scottike]

My first thought would be a heat problem with the electronic speed control.
Try troubleshooting by spraying the components with canned air or a non-conductive, non-flammable contact cleaner that will cool the components down rapidly. If that extends your run time before failure, you can start isolating individual components or just get a new board on the way.

[rohart]

Have you opened up to see the circuit board and blown it free of dust ? And that goes for the electrical end of the motor too.

If the large driver transistors were failing, cooling them would bring them back immediately. If it's some more subtle part of the speed sensor circuitry, cooling the driver transistors will have no effect.

[goose]

I know nothing of sewing machines (but they are delightful to watch in action). But sometimes sluggish motor activity may be as simple as lack of lubrication. This may be creating enough friction to either physically jam operation or kick in a thermal override for the motor. Has it been a while since you've lubed and cleaned the machine?

[Greg Q]

Check the motor brushes. My wife's longarm (A-1) is five years old and is getting close to due for new brushes. Also, the start/stop buttons on every long-arm I've seen are pretty light-duty. Contact issues do crop up.

Does the machine work normally in unregulated, or is the problem evident in all modes?

Greg

[Tony Ennis]

Wife opened up the motor (!) and cleaned the brushes. This had no effect. Phone support guy said they were still good for a few years.

re: cleaning - the wife is meticulous about keeping the machine clean and in top operating shape. She's relentless, lol.

It fails with or without the stitch regulator in use.

It failed again this evening, so that's an average of once per quilt. Tolerable but I bet it starts getting worse.

[2ManyHobbies]

When the motor stops, does the handwheel turn freely or is it stiff?
Any difference turning the handwheel when it has been sitting?

[Greg Q]

Just to back-track a bit: Is the fault in the motor only? Do the lights still work?
What brand of machine is it? And, when the motor fails, can she still rotate the thumbwheel freely to take a stitch manually?

Greg

edit: On her machine is there any way to bypass the switch on the grip? They are the ones that fail over time. Columbia River and Kingsmen stock those for most machines (as do other long arm suppliers)

[Tony Ennis]

When the motor stops, does the handwheel turn freely or is it stiff?

Don't know, I didn't think of that until after we reset the machine this last time.

Any difference turning the handwheel when it has been sitting?

It pretty much freewheels when unpowered.

Is the fault in the motor only?

I'm not sure.

Do the lights still work?

yes

What brand of machine is it?

Gammill

And, when the motor fails, can she still rotate the thumbwheel freely to take a stitch manually?

She didn't try that.

On her machine is there any way to bypass the switch on the grip?

Sure, I just fixed it - when she was troubleshooting she pulled a wire out of it. I could use alligator clips to short the switch, but it isn't a common switch. While experimenting I disconnected one wire from the switch while the machine was running and the machine did not stop. When I reconnected the lead, the button stopped the machine properly. That was unexpected.

[Greg Q]

Hi Tony...Those switches are momentary contact type. In fact, I think Radio Shack carries them (do they still sell stuff like that there? Here in Australia I think they are out of that business).

I'll see if I can find in my files a link to a long troubleshooting file that I have or had somewhere.

So it's fixed now?

Greg

On edit, here's the link to one supplier that my wife has used happily:http://www.kmquiltingsupply.com/Parts/Switch.asp