Interference From Plasma Cutter Freezing FireControl

Since beginning the delivery of CrossFire PRO machines, our number one priority as a company has been to chase down issues and offer permanent solutions to them. This is evidenced by our frequent updates to THC firmware and FireControl to fix known and reported bugs and also to add functionality requested by the community. The total number of reported issues has plummeted in the last few months which we are really proud of, but we are still not where we want to be.

There are two issues that we have been seeing more frequently than we would like to fix. One of them is FireControl launching issues which we are working on intensely to solve. The other, and what will be discussed in this thread, is the interference/EMI problem. For those not familiar with this issue, check out this thread: FireControl Freezing During Cutting & How to Fix it!

After delivering all batch 1 and batch 2 machines, we found that about 70% of users are able operate without any clip on chokes. Approximately 25% need 2 chokes with the remaining 5% needing two or more. Obviously this ‘solution’ is something we have never been satisfied with so we started really looking into our board design to figure out why it is so sensitive to EMI and what we could do to bolster it.

After testing a lot of different theories, we found that a single SMT inductor was the source of the problem. For those not aware, the D+ and D- USB data lines are usually pulled to ground with weak pull down resistors. This is to ensure that the data lines aren’t ‘floating’ which is good for EMI resistance. An inductor is placed in series between those resistors and the ground plane which follows standard USB guidelines. That inductor is great for ‘trapping’ noise that emits from the board, but it turns out that the inductor acts like a receiving antenna to funnel noise emitted from the plasma cutter straight to the data lines via the pull down resistors. Noise on data lines is BAD.

Through testing, we found that removing the inductor and soldering a short between the solder pads dramatically improved the resistance to EMI. We have an AHP plasma cutter that is a particularly noisy emitter that requires the use of multiple chokes (3-6 depending on the computer that is used). By shorting the inductor, we are able to run the AHP using a cable that not only doesn’t have clip on ferrites, but also does not have molded ferrites either.

We will be performing this modification to all of our motion control board inventory so that future customers do not experience this issue. A 0 ohm resistor will replace the inductor on subsequent manufacturing runs.

If you currently have a batch 1 or batch 2 machine and wish to make the system more robust to noise, we strongly recommend performing the mod as follows:

Step 1: Using needle nose pliers, remove the inductor labeled L1

Step 2: Solder a short (aka a solder bridge) across the two pads

Step 3: Reinstall board.

Since we have only tested this on our shop, we would love to hear the communities experience with this modification. If you are having interference problems and don’t feel comfortable doing this mod on your own, feel free to send us your board and we will do it here.


Won’t this increase the potential for noise to emanate from the control box to the outside? Wouldn’t that change your FCC certification (needs to accept interference from external devices, must not interfere with external devices)? Or does that not apply because it’s industrial vs consumer electronics?

I would certainly be interested in other users experience after the modification, especially those that have had to add ferrite chokes. The EMI interference was one issue that seemed like it needed the chasing down Langmuir has performed.

So, as a man with 6 LS provided chokes and a USB isolator, I seem to be a candidate for this particular procedure. As a total electronics noob, my guesses are you either mean for me to build up solder from point a to point b or to solder a short piece of metal that bridges the gap. Is either guess correct?

yes to either. I think the pads are so close that you can just bridge it with solder across.


Hello, sorry but I am fairly new to forums. I have just performed this mod and it is so close I just built up solder but you have to be careful not to put to much heat into the board (as I believe I was). It has seemed to completely fix my EMI issue as I was unable to even get a small cut from my table, but now have consistantly been able to cut my test peices. This being said my THC is not recognized at all in the firecontrol anymore. ???


Thanks, Joe.

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Awesome FAB.TY. I’m headed to my shop to do it now.

Are you positive that you have installed the THC in the proper orientation (assuming you removed it to perform the mod?)

Yes you are absolutely right, I removed the cover and the THC board, then re installed it. I believe it just wasnt in making contact as you said. It is now recognized in fire control. I will test cut more tomorrow and update, but as far as I know this has completely fixed my problem. THANK YOU


I have made the modification but no cutting as yet. I am still setting up the shop. I did load the break-in program and it jogs just fine.

I had horrible EMI right out of the box, couldn’t cut anything without my laptop freezing. Just made the mod. It took less than 10 minutes. Cuts like a champ now. Thanks!


@langmuir-daniel How about a video on this? I think alot of us are having issues with this still. Seeing is I am not an electrician or have much experience soldering, it would be nice to watch someone do it.


Random thought, may not work, just an idea. What if instead of removing the inductor it gets covered for those that dont want to solder. I wonder if maybe putting something over it would stop some interference. Hot glue, silicone, electrical putty. Just a thought…

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maybe its noise running thru it that’s the problem . i’m not sure covering it would make a difference but i could be wrong.

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May be correct, I was just under the impression it picked up noise like an antenna. Just spitballing

Hey we are assembling our machine #11699 and saw this thread…what batch was my shipment in so I know whether I have to make this adjustment.

probably easier to just to take off the cover and look to see if it’s there or not. you’ll have to open it up to install the TCH module anyways.

So if that little L1 is there I have to solder? Yuk…