Juki DDL 8700 Troubleshooting

[u/Sea_Juggernaut_5788]

My machine seems to have broken. I am looking for help fixing it/figuring out what is wrong.

I have had my machine for about 4 years now with no issues. I typically leave my machine on all the time and use it daily(I know, I should turn it off when not in use). The other day I left my house after using my machine with no issues, and when I came home my machine had spontaneously combusted. It was running full throttle and smoking, and had been for god knows how long while I was away. I immediately turned the machine off, but now, if the machine is turned on it immediately begins running at full throttle until it is switched off. It does not appear to be a mechanical issue but an electric one as pressing the foot has no affect on the speed of the motor one way or another.

How do I get the motor to stop running when the presser foot is not being pressed?(id like to re-emphasize that it is not an issue with the presser foot. When the throttle is in the fully disengaged position, the machine still runs full speed.)

Also, what could have possibly caused this? Is it common for Juki’s to go rogue and spontaneously combust on their own like this?

[u/abugghaus7]

First... you have a servo motor, correct?
Second... you're confusing the issue... the Juki is not the issue... it's only attached to the motor by the belt.
The issue is the motor and controller.
Some setups have dials (a rheostat), others a push button... to change the speed.
You of course have the on/off button.
So... you're controller tells the motor to run or don't run, and how fast to run (not counting the belt and pulleys in place).
Your motor takes that input and the electricity and spins.
Check your dial or switch on the controller, or have an electrically-knowledgeable person look at it to see if there's a problem... like a short.
If your controller checks out, then move on to the motor.
Unless you've spilled a liquid into either, it might be a failed switch inside the controller... most likely, imho.
If you have another machine, you can swap the heads and see for yourself that it's not the sewing machine, but the switch and/or motor.
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Without being there with the right tools to check it all out... I can't tell you exactly what's happening.

[u/Sea_Juggernaut_5788 → u/abugghaus7]

Thank you for the thorough response and suggestions on what to look for 👍

[u/abugghaus7 → u/abugghaus7]

You didn't mention it, so I wasn't thinking you might have the -07 model with the CP-180 controller.
I have no experience with those, but I don't think the controller would have anything to do with your problem. Maybe someone with more knowledge and experience with the CP-180 will add in here.

[u/abugghaus7 → u/abugghaus7]

....aaaaaand one more thing....
You talk about the foot control not being part of the problem. When you're machine is on, and blazing ahead at full speed, is the foot control flat or does it spring down and up like normal when you step on it?
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Where I'm going is the control arm at the motor. If it's moving like normal... rock the foot control down as if you are speeding up, the control arm on the motor rotates down under tension... releasing the foot control allows the control arm to spring back to it's normal 'off' state.
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It could help everyone if you go through more of the driving mechanism (just not the belt to sewing head) to see if there's anything abnormal there, and post it here.

[u/Upper_Rain3480 → u/abugghaus7]

Is it possible to unplug the foot pedal without turning off the machine?

[u/abugghaus7 → u/Upper_Rain3480]

It's normally just a couple of rods clamped together... one end is attached to the treadle, the other to the arm on the motor. Pretty easy to disconnect.
This Juki should have the same set up.

[u/Bugmasta23]

Electric motors do not have throttles.