FSL 5th Gen Potentiometer

Machine: Full Spectrum Laser 5th Gen

Board: LaserBoard

Firmware: n/a - not there yet

Hello Everyone, and thanks in advance for your input. I am wiring up a Laserboard to replace the stock FSL controller. In the process I am installing an ammeter and a laser fire button. I have most everything wired, but before connecting the laser fire/ground to the Laserboard (and even powering Laserboard) I wanted to make sure the Laser fired properly with new button etc.

Using 10-turn pot and ammeter purchased from cohesion, wired as diagram attached depicts.

Pot might be wired wrong, maybe 5v/ground flipped as counter-clockwise seems to increase power.

Laser Power Supply makes a skrrrrrrr sound when test firing. register about 4 ma on meter. When I increase potentiometer (counter-clockwise) and fire again no skkkrrr sound and gauge jumps past 20ma.

Ok you say find the sweet spot between those situations. Nope, seems to be either or. I am about 1 turn from the end of the pot, and the tiniest change will jump between those two outcomes. Didn’t test too much as the 20ma consumption seemed too high.

Thoughts on wiring? I currently do NOT have the laser fire/ground connected to cohesion laserboard, so there is basically no connection to board currently.

hmm. new users cannot upload images. maybe this link will work:

Doing a little more testing now, looks like the resistance in the last turn jumps dramatically from 10k to 0. That might be what I’m seeing…

Found the spec sheet for the pot I got. Got it wired up so CW goes up not down. Current wiring:

Pin 1: Ground
Pin 2: Input
Pin 3 : 5v

Something is weird with the pot though. Reading voltage on Pin 2:

Maximum counter-clockwise: 0v
One turn: 3.8v
Turns 2-10: slow climb from 3.8v - 5v

Do I have a bad pot? Something else to test?

Hi Rob,

Welcome to the forum! I have upgraded your trust level so that you can now upload photos.

For installing the potentiometer, switch the wires to 5V (pin 1 - in the middle), IN (pin 2 - on the bottom), and G (pin 3 - on the top). This is the correct orientation for the potentiometer we offer.


Let us know if you still experience issues after wiring the pot correctly. Please provide clear pictures of your machine, control panel, other electrical components, and wiring. We need to see how and where everything is connected. Double check the mA wiring just to make sure it’s connected properly as well.

Make sure the coolant(s) you are using are not conducive. Distilled water is preferred. The linked article covers some other additives that are safe to use to maintain your cooling system. I’ve used the Secret Recipe with zero negative effects.

If you experience the screeching while firing after hooking up the LaserBoard, it’s likely because the machine needs to be tuned to use PWM.

1 Like

@Starla thanks for your well considered response. Here is where I am at:

I wired potentiometer to your provided diagram, which had me flip the G/5v connections.

(Yellow = IN, Red = 5v, Green = Gnd)

Tough to get photo, but I think you can see those wires at the top of the middle block.

This is my current wiring.

Wired this way the power used on Ammeter goes DOWN when I turn CW, and UP when I turn CCW. No big deal, but looking at the wiring schematic it looks like pin 3 should be the 5v? Anyway, far CW turn i get almost no reading on meter, and no laser. As I turn CCW it slowly creeps up to maybe 10ma. Then at about one turn from maximum CCW it jumps beyond 20ma. There is a little spot in there where from then on its basically not a resistor at all. This correlates to measuring with ohmmeter.


And speaking of current readings here is a pic of ammeter wiring:

That’s from before rewiring potentiometer, so ignore the Pot. White wire on ammeter goes to laser tube (-). Red wire is going to (L-).

And thanks for you note re: distilled water, that’s what I’m using.

And just for fun, here is a pic of the ‘pretty side’ of the panel, waiting for this to get competed!

Look forward to hearing from you, thanks for taking time out of your day to assist!

I am still working on finishing my 5th gen conversion. Maybe even tonight.
I am looking at your latest schematic and you have the Cohesion Board going to ground and “L” on the 4 pin connector that has 24vdc, G, 5V and “L”.
I am looking the Power supply printout I have for my 5th gen and that “L” is not used.
The “unofficial” schematics for the 5th gen also has this labeled as “not used”
I think maybe the laser fire should be tied to the “L” where you have “test fire” hooked up.
That is where my 5th gen board was hooked up with a green wire from power supply to FSL board and that is what the schematics show.
Maybe both “L”'s go to the same place so I might be totally wrong.

Hi @TomTheWhittler. Thanks for replying and good luck on your conversion. Also, please check out my other thread, I’d love to know if you got your endstops working!

Regarding the “L” - I am still learning but I saw somewhere that the “L” on the center block and the “L” on the right block are connected internally in the power supply. Think its normally -4v and grounding it fires the laser. Again, I’m just learning and reading here.

If they are not connected which is my current working assumption, then I hope someone pipes up! :slight_smile:

For closure on this thread, I replaced the potentiometer and that fixed the problem. Final wiring for me is as pictured below. Turning clockwise increases power.

(Yellow = 0-5v Input)

Hi Rob,

I’m glad you got the potentiometer sorted! To clarify, did you replace another pot with the one you got from us (which is working) or you had to replace the one you got from C3D?

I replaced the one I had originally gotten from C3D with one I sourced elsewhere.