Laser works in manual mode, won't fire when processing Gcode

I need some help.
I’ve read the other posts and have made all the recommend adjustments, but I just can’t get the laser to fire when running a Gcode job.
Works just fine when I flip to manual mode - burns the test wood all day long.

I created the job in LightBurn.
I’ve set all the variables based on what I’ve read here, Tool Type PWM Spindle with Rapid Auto Off and Dynamic Power Off.

Verified LightBurn Basic Device settings is set to “enable Laser Fire Button” is green, (on)
General Light Burn settings (Gear) beinner mode is off, Better for Diode = Inches/min

The Device is a JTech laser Pro, is set as GRBL-M3 1.1e or earlier.

It may be telling that when I manual enter M3 S10 then press Play, on the manual code entry screen it also DOES NOT turn on the laser.

It’s as if the laser just never gets the commands.

I’ve even tried removing the laser extension cables, Still no luck.

Please help what am I missing?

Hi, I had the same problem, when I changed LightBurn to GRBL it did work.


I have the exact same issue and I’ve followed the lightburn AND Inkscape tutorials through jtech and still can’t manually or gcode turn on the laser. If I push the physical button to test it turns on full power…

I found the cable between the main controller and the laser to be bad. It’s just a two conductor wire. I tested it with an ohm meter and one of the two wires was broken. Buggered it together and it’s working, Will need a new cable.

I am using Vectric VCarve Pro and I am having the same problem. With the small switch all the way to the left it works but the laser is always on and leaves a trail when it skips to another vector. With the switch all the way to the right ( which the install video says will only fire with the G code) nothing happens.

Having the same issue. The moving mode selector switch to left will fire the laser (at full power), confirming that the laser works. Trying to send gcode (M3 S10) through the MDI interface does not turn on the laser.

Confirmed the Tool settings match what was shown on

Checked cable with multimeter, both side sof the wire have good connection through the connectors.

Glad I’m not the only one with the issue, but eager to understand the problem.

I’m getting the exact same issue. Did anyone figure out the problem. I’ve checked my wires and I have continuity.

I had the same problem and ordered new cables from J TECH (5 ft instead of the 10 ft that came with the laser). Customer service at J TECH overnighted a new control module. The new cables and the New controller arrived the same day. I thought I would install the new cables first to see if that could be the problem before installing the new controller. I discovered that the cable going from my Onefinity controller to the J TECH controller had not “seated” correctly. When I reseated the cable every thing worked fine. J TECH’s customer service is fantastic. I shipped the new controller back to J TECH with expressions of gratitude for their great customer service. My problem had been “user error”.

I’m not having any issues running gcode to it using vcarve pro. Make sure the tool type is set to “PWM” and that you’re using the post processor for LASER. The laser tool should be setup as described here.

Hopefully this helps.