Laser not firing after installation of Cohesion 3D board

Machine: Large K40 variant with digital power control

Board: Cohesion 3D board

Firmware: Smoothie

Problem/ Question: After installing the Cohesion 3d board the laser doesn’t fire when performing engrave/cut. The head is scanning as if performing the engraving process but the laser isn’t activating during the process. If i press the test button the laser will fire but nothing otherwise.

After checking with a more detailed engrave/cut piece, the laser is just scanning the entire frame rather than each seperate engrave/cut.

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Hi Stephen,

Welcome to the forum!

Can you also provide a picture of your LPSU connections?

Review the lights on the board and make note of the LED Sequence. Do the LED status lights indicate “Normal Operation” mode?

Run the following test:

  1. Type the following GCode in the LightBurn console to test. Ex: G1 X10 S0.8 F600

  2. Hit the Enter key to send.


  • G1 indicates this code is a cutting move.
  • X identifies the axis and the numerical value is the position coordinates to move to on that axis.
  • S is the power parameter. The example above is set to 80%, but you can try an S value of up to S1.0 (100%).
  • F is the feedrate per mm/min. The example below (F600) is 10 mm/s.
  1. The head should move while firing. The red status LED “Laser Fire Status” in the bottom left corner of the board should turn on (below the laser power and laser diode out screw terminals on the left side of the board).

Is the laser head moving while firing with the LED lighting up?

The pictures you added didn’t come through unfortunately

When the laser is idle the series of LEDs are showing as normal. I typed in the code and although the head moved, the laser didn’t fire nor did the red LED light up.

However when i set a task running the LED lit up, though the laser didnt fire

Thank you for the picture and video, Stephen.

Confirm that your memory card is being read properly and refresh the firmware.

  1. With everything powered down, remove the SD card from the LaserBoard.
  2. Reformat and flash the memory card again from the instructions at the bottom of the previously provided LED link.
    a. The card should be in FAT32 format. When flashing, the filename should change from firmware.bin to FIRMWARE.CUR in the contents.
    b. If it is not formatting or reading properly, attempt these steps with a different memory card.
  3. With the power off, add the freshly updated memory card to the SD slot on the LaserBoard.
  4. Power up and try the test command above again.

Please let me know the results.

Still the same results. The head moves, the LED lights up but the laser doesn’t fire

The Y axis is also inverted now

Thanks for testing that, Stephen.

Try the following steps to determine if the issue is on the laser end or the board end. We are going to replicate how the board “talks to” the LPSU, but remove the controller from the equation.

With the machine off, unplug the power from the LaserBoard. You do not need power on the board for this test.

  1. Remove the large white power connector from the board.

  2. Work on the connector somewhere where it will not touch anything conducive.

  3. Power the laser machine back on.

  4. Set the digital keys to a low power setting which is high enough to trigger the laser.

  5. Use a short piece of wire to connect the contact metal of the Laser Fire (L) and Gnd (G) ports on the connector. This simulates completing the circuit.
    image image

  6. Turn the machine power back off, allow the power to discharge before making any further wiring changes.

Is the laser firing when shorting the wires on the connector?

Invert the Y direction in the board config (beta dir pin) and add or remove a ! after the pin #. Use Sublime Text to make the edits. Make sure the board is powered down when removing and reinserting the card.

beta_dir_pin                                 0.11!             # Pin for beta stepper direction

I removed the socket and shorted the pin as shown. When i hit the test button the laser fired as normal.

Adding the ! to the code moves the head to the bottom corner and it keeps trying to move to that point until i turn off the machine as there aren’t any switches at those points.

I can live with it being inverted but not the laser failing to fire :slight_smile:

Thanks for this help. I went for the C3D board as it was plug and play… didn’t expect these issues lol :slight_smile:

Hi Stephen,

We are sorry you are having issues with the board. This is not the typical experience. We are trying to determine the cause. Thanks for your patience during the diagnostics process. We’ll make sure you are taken care of.

Revert the pin in the config file. Make sure your Device Origin is set properly. In LightBurn, Edit > Device Settings and set the ‘Origin’ to the front left (lower) corner. Please let us know if that resolves the inversion issue.


I am checking to see if there are any other options we can test for. In the interim, there is a known alternate wiring configuration (as shown in the photo below) we can test:

  • Remove the large power plug from the board.
  • Laser Fire (L) goes to “FET -”, the lowest screw terminal pin along the left edge (indicated with yellow line).
  • Ground (G / GND) goes to the board ground, the top left screw terminal right pin (indicated with black line).
  • Note: This is hooking up to the actual ground plane of the board, so there is no longer protection afforded by the opto and damage to the board could occur with any power spikes, invalid wiring, etc.

Once you do that, try inputing G1 X10 Y10 S1.0 F600 as a test into the console and let us know what happens.

Thank you for your time with this. Issues happen so that doesn’t bother me to be honest. Nothing is ever 100% perfect all the time :slight_smile:

Reverting back to the original code has stopped the issue of the head constantly bumping on the bottom of the y axis. It has gone back to being inverted but i can live with that.

What is the risk of damaging the board if i screw directly onto the board? I dont want to damage it in case there’s a way of fixing the issue of the laser not firing

Absolutely. Happy to help! This is the known work around for fixing the laser not firing issue. Please standby until I hear back on any other options and then we will proceed.

ok, will do :slight_smile:

Any luck with this? It looks like this is a board defect so the easiest thing to do is have it replaced

Hi Stephen,

I’ll follow up with you later today with more info. Thanks for your patience.

Ok, thanks :slight_smile:

Hi Stephen,

For this step, the laser should fire as soon as you short the L and Gnd pins. It should not require pressing the test button. Can you perform this test again with the previously listed post #7 and provide a video of how you are testing it?

We would like to see the wiring on the board in its current state, please. We’ll address the inversion later.

Here’s the video of the test following the image you provided to close the circuit to fire the laser. It doesnt fire the laser but you can see by pressing the test button 3 times i was able to fire the laser

Here are the pics of the wiring

Do you think its a wiring issue? Something none standard would be just my luck lol :smiley:

Hi. Any luck on finding a solution?

This is it running the old Nano board and K40 Whisperer

Hi Stephen,

I’m getting caught up on posts from over the weekend. Thanks for your patience. This is definitely not the usual case, so it’s taking a bit longer to troubleshoot.

I’ve been doing some digging the last few days and others that have had laser firing issues with a similar setup to yours turned out to be a wiring issue. Can you provide pics of the other components in your electronics compartment, please? Any additional information and photos could help us pinpoint what it could be. The fact that the nano is firing is what is interesting. Can you provide a pic of that as well?

No worries. Its just something i’d like to get sorted then i can use the better software lol. K40 Whisperer isnt all that stable and misses things lol.

I’ve re-installed the Nano as i needed the laser running so i’ll get pics once its finished the current job

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