Carbide Motion - GRBL Error when router is turned on

I periodically have a problem where Carbide Motion disconnects from my S3XL with the following error message:

GRBL Error: Serial Port Unknown Error

Typically it occurs when powering up the Dewalt router. When I first set up my machine it occurred frequently, so I replaced the plain USB cable with one that has a ferrite choke which made a big improvement, but it will still occasionally disconnect. Apparently noise in the lines is the issue.

All of the outlets in my shop are on the same circuit which means that the PC, S3, and router are all on the same circuit. I had a large batch of parts to run on this weekend and I didn’t want to deal with GRBL crashing so I ran an extension cord from the router into the next room (which is on a different circuit), and I was crash-free with a good 50-60 on/off cycles of the router.

What is the best way to attenuate this crosstalk between the router and the machine controller? Could it be as simple as buying a high quality USB cable or do I need some sort of filter on the AC lines?


  • Dan

I had this issue a couple of times. I found if I used a low power USB port and long cable I’d get the issue more often.

I still use a long cable but use the high power USB port with my laptop.

If I use a short cable I rarely get the issue at all.


The community has collected a number of things to try:

If your machine is still under warranty, if the basic things above don’t work for your situation, please contact and we’ll set this right.

Even if your machine isn’t under warranty, if you still have this problem, despite trying whatever of the above makes sense for your situation and which you are comfortable with, contact — we will work something out to ensure that the machine performs to its specifications and your satisfaction.


I had a lot of the same issues and tried many of the things listed in the Wiki. I did buy the newest controller from Carbide 3D ( I was running the original SO3 2.1 controller board), but the things that seemed to make the most difference for me was adding a switch to turn on and off the router and routing the power cord for the router the other way (away from the controller). I have had zero issues since doing both of these things.


I’ve had the same issue, over a quite long period of time. What I’ve found so far:

  1. Use a short USB cable (decent quality)
  2. Don’t use the same outlet as a compressor or a vac (or another possibly noisy consumer) is connected to
  3. If still problems, use a different outlet for the spindle (as a side note; the Makita causes more “serial errors” than the Dewalt…)

Edit: And 4) don’t route the power or USB cable for Shapeoko together with any other cables, keep them separate


I had this problem when connecting to my Surface Pro 4. My surface would recognize I was connected to a Shapeoko 3 but Carbide Motion kept giving me the “GRBL Error: Serial Port Unknown Error” I bought a powered USB hub (link below) and it solved the problem.

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