No Laser Fire Status LED & laser doesn't fire, but test fires with control panel

Machine: K40


Firmware: Smoothie

Problem/ Question: Converted my K40 last October. I’ve used it 15 or so times since then. Fired it up the other day and the control still homes the machine, moves the axes, triggers air assist, but won’t fire the laser.

The laser does fire if I use the test fire button on the physical control panel of the machine.

The control thinks it is firing the laser as shown in the console, but the Laser Fire Status LED on the corner of the LaserBoard does not light.

Removed the board from the machine and have it on my electronics bench. PSU is connected and USB to computer is connected.

Placed a meter in continuity mode across the 24v and GND on the laser connection at the board and ran a test program as well as used the test fire button on the move tab. No continuity during firing, or when not firing.

PSU that came with the board is outputting 24v as expected, all other LED’s on the board are lit solid and/or flashing as described in the troubleshooting documentation.

Seems to me something has died. Inspected the board under the microscope and no obvious signs of damage or magic smoke. Solder joints look good. Nothing dropped or cold.

If there are any test points or locations on the board where I could hook up my scope to sniff out where the signal (see if the SOC is actually sending the signal in the first place, etc) let me know.

If not, seems a pretty clean case of: it probably needs to go back to have you look at it.

I look forward to hearing back. Thanks!

Also forgot to mention, hooked my meter in diode test mode to the laser fire status LED and it lights as expected, so the LED functions correctly.

I received a new board with a similar issue.
It is possible the optocoupler is fried or died which is built in safety feature. You can bypass the optocoupler however do so at your own risk as you can completely fry the board if you wire it incorrectly! Check out my post Laser not firing issue

Looks like we don’t quite have the same issue.

In the 4th image down on your post I see that the onboard laser fire status LED on the LaserBoard is lighting up (LED in the upper right of the image).

That LED does not light for me. That seems to indicate that the board is not actually sending a signal to fire the laser, even though it functioned correctly the last time it was used.

I missed reading the dead led! An interesting issue which unfortunately I can not help you with. Just hope that Cohesion Support will be able to help. A full schematic would help you but I doubt they will provide that.
Good luck.

A schematic would be amazing. I’m sure they don’t hand it out to protect their IP, which I can completely understand. For those of us who have the background and equipment to do low-level troubleshooting, it would be hugely helpful though. I’ve held off on digging in too much since I don’t have a ton of free time, and they might be aware of a common failure mode that fits these symptoms.

Fingers crossed!

Did some snooping for the hell of it. Not the optocoupler. The fire status LED and the additional 5v PWM output pins are pre-optocoupler, and neither of those are triggered either.

Looked further upstream and have come across a couple of IC’s that I can’t identify based on their part numbers. If I can figure out what they are, that might point to a solution.

5V is showing up at U4, but nothing past that. ZY2PG isn’t a part number I’m familiar with. I have a suspicion of what it’s supposed to do based on where it is in the circuit, but it would sure be handy to have some input on the issue. Especially since it appears that the output of it relates to that 5v output for everything that isn’t functioning.

Screw it. Pulled out the scope and started probing.

Pin 68 of the ARM is what outputs the PWM to fire the laser. Using the Fire button on the move page in Lightburn produces a 5khz square wave on Pin 68. Cool.

That 5khz goes to U4, which I suspected as being bad. Again, I can guess at what U4 is, but would love input from C3D. Pinout is as follows, but not sure what is Pin1 since there’s no marking.

Output to Alt +5v PWM Out / R47/etc ======||======GND
------------------------------------------------------------||======Pin 68 Input & R36 (optocouple)
5v Input from SJ3 (5v fuse bypass) =======||======GND

5V goes in, but no voltage is output when firing.

The “Pin 68” input gets pulled to ground, which explains why the optocouple isn’t firing, and explains why no voltage is output either.

Makes me think U4 is dead.

Again, any confirmation as to what ZY2PG is would be great.

Hook channel 1 on your scope up to the “alternate PWM out (5V)” pins. If you’re getting signal there then hook it up to the “laser diode out” terminals and give it a shot. If you’re getting signal there, flip the board over and connect it to pin 1 (upper right if the board’s text is in the right orientation) of the optoisolator. The optoisolator is acting as a contact closure for the laser’s L+/GND terminals, so you should see a low (but not zero) resistance connection between LASER FIRE and GND. Note it’ll be PWM unless the laser’s commanded to fire at 100%.

Anyways, if you get signal on pin 1 of the optoisolator but no corresponding signal on the output of that isolator the isolator itself is fried and will need to be replaced. Let me know how it goes.

Edit: I somehow missed all your messages in between your first post and now. Disregard the above while I look further into what’s going on.

This is a 74HCT1G125 tristate bus driver acting as a 3.3V to 5V level shifter to drive the FET controlling the Diode Out lines and the Alternate PWM out. It’s possible it has failed and is pulling the output of pin 68 to ground. However, the optiosolator (above R36, unlabeled - Lite-On LTC-217-G, because I know that will be your next question :slight_smile: ) is driven directly from the 3.3V microcontroller pin.

U4 should be safe to remove entirely if you are not using the diode out or alternate PWM out pins for anything. Give that a shot and see if it springs back to life.

Thanks for the info! Had a feeling that’s what U4 was. Thanks for the confirmation!

It dawned on me to check the voltage of pin 68, and noticed that the PWM output is just shy of 250mV, even though the 3.3v regulator pins are all reading a proper 3.3v.

I doubt 250mV is enough to trigger to optocoupler or the level shifter. Being a digital pin, I’d expect 3.3v.

Even with U4 and the optocouple removed from the circuit, it’s still reading low. Thoughts?

And thanks again for the info!

Oh, and the laser diode out also doesn’t output any voltage.

If the tristate should cut power to the diode when the laser fires, then that might point towards a common fault?

If it’s reading that low then the pin on the microcontroller may have gone bad. I need to dig out the schematics I have somewhere around here and see if anything else could have failed, grounding that output.

I appreciate the assistance!

Checking in to see if you’ve come up with anything else yet. Thanks again for the help!

Sorry about the delay - I have been slammed with work and just got a chance to take another look at this.

After reviewing the schematic it looks like the only things on pin 68 are U4 and the opto. I think the pin on your microcontroller somehow went bad, and I’m not sure how that would have happened.

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.