Laser trickling out

Machine: K40 with digital power readout

Board: C3D LB

Firmware: Smoothie
Software: LightBurn

Problem/ Question: After I received the K40, I installed the C3D laser board promptly and connected to my Mac. I got so excited I didn’t install the mA meter like I should have. After lasering a bunch of stuff, I came to my senses and decided to install the mA Meter into the HV return line to the LPS.

Installation went great. Until I turned the machine on…

The power display board had partially stopped working. None of the buttons or the display functioned, with the exception of the laser fire button, which still functioned admirably. The C3D operation still functioned great with the exception of the laser. Which did not work…fully. The laser does come on and stays on at about 4mA, barely noticeable burn. Stays on. Until I power cycle the machine. But it never does go up to operating power.

The test (text) button still fires the laser, and the test fire button on the display board does fire the laser. It also, however, maxes out the mA meter for while the laser is firing. The adjustment buttons no longer function on the power display.

I removed the meter and tried again with the same issues.

I ran the test in Laser not firing - new laserboard and got the same result with no continuity while running the test in both situations.

The red light does come on when it should be firing.

Any assistance as we quickly approach Christmas would be very helpful, thanks in advance!!!

Original wiring of the laserboard

Original power display

New mA meter

Current wiring of Laserboard


Power Supply Wiring after removing power readout board - 4 empty terminals


Backside of mA Meter


Original Board - m2 Nano

The second image of The laserboard, shows the connections having been soldered to the terminals. There was a lack of continuity between the PWM terminal (yellow wire) and the terminal post adjacent to it, so I went with what had worked prior by soldering it in an attempt to eliminate any variables.

This image shows the laser fire power. The JWH that is easily visible, was done in 5 passes. The JWH that is barely visible was a single pass.

In the pic where you note ‘4 empty terminals’ - the three terminals to the right are for power regulation. In the configuration you have it in, I’m surprised the laser fires at all, honestly.

Since you’ve disconnected your DRO and apparently don’t want to use it at all, (this is fine) those connections should be replaced with a 1k or 10k linear potentiometer (Ray has an awesome 10-turn pot for sale on his store). If memory serves, the pinout of that 6-pin connector, from left to right, is: H1, H2, L+, GND, IN, 5V. H1 and H2 are required to be connected for the laser to fire and this on a K40 is your front panel “laser switch.” The “laser test switch” normally sits between GND and L+ on this connector, but with the digital panel out of the picture this will be non-functional. The remaining three terminals are where the potentiometer will go. Connect GND to the leftmost terminal of the pot, +5V to the rightmost terminal, and IN to the wiper (middle terminal).

Without going into too much detail, the maximum power output of the LPSU is controlled by an analog voltage 0-5V on the IN pin. The potentiometer acts as a resistive voltage divider here to provide that voltage.

The digital panel works a fair bit differently and the explanation of that is a bit long-winded and more than I want to get into here - suffice to say the pot is a better solution overall for the way we’re controlling the laser.

Anyways, if you aren’t getting output how you expect it, the fact that IN is left floating is likely the reason.

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Awesome. Thank you!!

When I installed there must have been some static issues that caused the drop to fail. This has been super helpful in getting the pot installed and the bulb power reduced dramatically to improve lifespan. Or so I’m told…

When I ran a test from Lightburn, I still seem to have some disconnect. Lightburn will not fire the laser as it has in the past. Again, the red light at the bottom of the LaserBoard seems to be flashing relative to the intended burn. Is there a diagnostic I can run on the LB to see if it is functioning normally?

Is there something I’m missing? Thank you in advance for helping me out.

I realize now I gave you some bad information. I’m going to correct my post above to have the correct pinout and wiring and add some more information for you here.

If you’re seeing the red light fire on the laserboard when it’s supposed to be firing the laser, then you know LightBurn and the controller are talking properly.

To set the pot properly, start with the pot turned all the way down (full counterclockwise). Put something sacrificial under the laser head and hold down the laser test switch (your machine is missing this because of the failed digital panel - this is a momentary switch between L+ and GND on either the 6-pin or 4-pin connector). Slowly turn the potentiometer clockwise until the ammeter reads 15 mA. Mark that setting. This is your maximum power.

With the pot set in the 15mA position, set LightBurn to draw a box or a circle or something set to 50% power and, let’s say, 100mm/sec. Send the drawing to the laser and you should see it sinking approximately 8-9mA.

Here’s a ghetto hand-drawn diagram of the proper wiring for your machine.

Note that there shouldn’t be any continuity on the yellow wire as you noticed - It’s the LPSU +5v output. Neither it nor the LPSU +24V (black) are used on the laserboard so it is safe to leave them completely disconnected.

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Thanks! I went through and removed the black and yellow from the LaserBoard and LPSU. The pot is working great to show the 15mA but so far I can only get the laser to fire by pressing the test button on the LPSU.

Any ideas why the laser wouldn’t be firing when the command is sent from Lightburn to print? Is there something in LightBurn I should be troubleshooting? Some G-code tests I should run?

Better pic of the LaserBoard

At this point, other than the x/y axis, there are only the two wires going to ground and L+.

Thanks again for all your help on this one!

Very concerning about the soldering wires to the power connector pins. The green screw terminal has the same connections!

Disconnect the green and white wires from the screw terminal. When you touch them together, the laser should fire.

Leaving them disconnected, put a multimeter in continuity mode and touch - probe to - on board (white wire terminal location) and + probe to L on board (green wire terminal location).

Issue the command that causes the red LED to come on such as G1 X10 S0.8 F600

When the red LED turns on, I don’t get a full beep like if you touched the probes together, but you should see something on the meter readout…

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I thought that might get some cringes. It was in an attempt (although ignorant I’m sure) to ensure that there was a connection between the terminals and the pins. At one point I was unable to get continuity between one of the pins and its adjacent terminal.

When the green and white wires are pulled out, and then connected, the laser does fire.

With the wires still out, I put the multimeter in continuity mode and tested continuity across the two terminals that the wires were in, specifically (-) and (L). I ran the G1 X10 S0.8 F600 test several times and ran a print as well. Both times the red light flashed but there was no continuity (OL) on the multimeter. In addition to the tack of beep, there was no readout on the meter.

Can you take a clear picture of the entire back of the board?

In particular there is a 4 legged long black rectangle under this area with the terminal and power connector, we want to see if any legs are loose, if there is any burning or charring on the board, or any evident damage to the component.

You bet. I could only find one 4-legged component.

There does not seem to be any loose components or charring.

That 4-pin device in the box labeled L217 is an optocoupler. The pins on the top in that photo are its input, cathode on the left and anode on the right. The cathode is tied to the system ground plane and if i’m following these traces right, the anode is connected in series with R36 and the microcontroller pin (2.5).

Leave the board otherwise disconnected from anything but USB and +24V power. Hook your meter in voltage mode up to the screw terminals labeled, “Laser Diode Out” - these are the screw terminals just below the 4-terminal screw connector. Run a test cut from Lightburn and check to see if you get voltage on those terminals when the laser is supposed to fire. If so, good - we’ll move on to the next step.

With the meter still in voltage mode, connect one end to a system ground point (the upper-left pin of the optocoupler should work - if that’s too difficult to probe use the ground pin from the power connector or the shield from the USB connector), then run your test cut again with the other side of the meter connected to the following points and report back if the meter does not read voltage on any of them:
R36 left-side
R36 right-side
Optocoupler upper-right pin

These should all read roughly 3.3V if the “laser” is set to 100% power for your test cut.

I ran the following test:

That 4-pin device in the box labeled L217 is an optocoupler. The pins on the top in that photo are its input, cathode on the left and anode on the right. The cathode is tied to the system ground plane and if i’m following these traces right, the anode is connected in series with R36 and the microcontroller pin ( 2.5 ).

Leave the board otherwise disconnected from anything but USB and +24V power. Hook your meter in voltage mode up to the screw terminals labeled, “Laser Diode Out” - these are the screw terminals just below the 4-terminal screw connector. Run a test cut from Lightburn and check to see if you get voltage on those terminals when the laser is supposed to fire. If so, good - we’ll move on to the next step.

With the meter still in voltage mode, connect one end to a system ground point (the upper-left pin of the optocoupler should work - if that’s too difficult to probe use the ground pin from the power connector or the shield from the USB connector), then run your test cut again with the other side of the meter connected to the following points and report back if the meter does not read voltage on any of them:
R36 left-side
R36 right-side
Optocoupler upper-right pin

These should all read roughly 3.3V if the “laser” is set to 100% power for your test cut.

My results were as follows:

Laser Diode out - 24VDC
R36 left-side - 2.64 VDC
R36 right-side - 1.22 VDC
Optocoupler upper-right pin - 1.22VDC

I will note that the laser was set to 100% power

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Looks to me like your laser fire pin either got really hot, hot enough to melt the solder or it might be just a bad solder joint. I would check with Ray and the gang to see if you would be voiding any warranty but if it were me I would re-solder that pin on the board. Looks like a cold or disrupted joint. Maybe take a closer look at it with an eye loop or a microscope if you happen to know someone who has access to one. I would check the other side of the board as well but I don’t know if there are any traces to that pin or not. If you are not sure of yourself with an iron, have someone experienced hit it. It needs to be hot and fast or you could damage the components in the nearby vicinity

At this point please don’t solder directly to any components on the board - we should wait for Ray’s official response when he gets back in the office.

Loather, is this a potential issue by R47? Just poking around the pics

No, the solder mask looks intact there. Plus, R47, R48, and Q3 are all part of the “alternate PWM out” driver and wouldn’t affect the “laser fire” path.