New analog panel on FL-K40D

Thanks, I will do that first!

Action #1: Please post or link to my schematic you refer to.

Action #2: Then I would change this wiring (picture attached):

  • Move the LPS-TL to the M2Nano-LO on connector #3 in the drawing
  • Connect LPS-Grnd to M2Nan-GND on connector #3

The above wiring changes are mostly to insure consistency with my experience.

Action #3: Test and see if the changes completed in Action #2 made any difference.

  • If not continue to Action #4.

Action #4: Test the LPS static power control

  • Connect a DVM between LPS-IN and LPS-gnd and set DVM to measure DC Volts
  • Turn the pot to the pot-value of column 1 in the table
  • With Enable Switch ON Test Fire the Laser long enough to get a stable reading on the ma meter.
  • Record values in the table below
Pot-volts IN Lma
1 xx xx
2 xx xx
3 xx xx
4 xx xx
5 xx xx

Pot-volts: this is value on the digital voltmeter on the panel
IN: this is the DC voltage on the LPS-IN pin
Lma: the value on the analog laser current meter on the panel in ma

To Fill in the table:
If you highlight the table above while reading this post
Then click “quote”
A reply post will open with the tables formatting in place
Don’t mess with the formating (|), just change the x’s to your measured values

Hello Don, This is the schematic I was referring to.

I moved the TL and Grnd connections.

I tried to do a test, but the computer was not recognizing my K40 (Tried different usb ports, replaced the Nano board with the other one I bought, but same results).

Do I need to send 5V from LPS to connector #3?

I’m stuck on action #2.

What do you think I should do?

The 5V supply is what powers the processor on the board as well as the limit switches. The 24V powers the stepper motors only. If you don’t supply 5V, it won’t function.

Thanks Michael!
I was wondering:
Is it safe to pull 5V from LPS to power the board and the digital voltmeter?
Do I need a (-) connection from 24V PSU to GND on Nano board also?

Oh my, Sorry, I did not notice that you had no 5V power to the nano.
I don’t know how this worked at all?

After you made the upgrades:

  • Did the Nano connect via USB?
  • Did your carriage move at all?

When I drew the conversion diagram above we did not know the 5V capacity for this style LPS. Most of these use a LM7805 which can source 1A, we assumed that was the capacity.

I looked around again and this time found a spec: 5V@ 20MA

It may be that my original drawing was flawed, or at best marginal. I am pretty sure it worked but I would not chance it. Poor supply capacity can cause a myriad of headaches.

I seriously doubt 20ma is enough to run the Nano properly.

These are the changes I recommend:

  • Insure all grounds are connected together including: 24V, 5V*, 12V*, LPS, Nano. [*if installed]

  • Add a 5V supply for the Nano. I would go for 3-5Amps. 1A is the stock supply source for the nano. Insure its ground is connected to the other grounds.

    • You can use one of these approaches:

      • Add a 5V buck converter to the 24V. There are many choices on amazon. Something like: I generally don’t like buck converters on logic boards because if they aren’t good designs they are noisy. It also depends on the capacity of your 24V supply? They really aren’t that much cheaper anyway. $12.5

      • Add a separate 5V supply: Lots of choices on amazon like this one: $12.5

      • Add a dual supply: Again, lots of choices on Amazon. This is a reputable supply maker and you get all three voltages 5,12,24 in the same supply. I use 12V alot for accessories. $23

Other questions:
Where does the wire (TO STEPPER MOTORS) go. Its at the bottom of your diagram and comes from -24V.

Next steps:

  • I would suggest amending your diagram adding your choice of 5V supply and then post here to review it before you purchase.
  • Purchase power supply
  • Install power supply and check wiring
  • After installation we should do DC measurements to verify the install.
    • Do you have a DVM and do you know how to operate it?

When you are done making the changes power up and please complete the table below.
Measure all these voltages with the ground lead of the meter on the same ground point.
Meter set to measure DC volts.

Location Terminal Voltage
24VPS +24V xx
Nano 5v xx
Nano 24V xx
Nano Gnd xx
LPS G xx
LPS 5V xx

To Fill in the table:
If you highlight the table in this post
Then click “quote”
A post will open with the tables formatting in place
Just change the values of the “x’s” to your measured values

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Thanks Don,
I think it was pulling 5V from the USB cable. I noticed the usb cable getting hot one time.

I was confused, this wire goes to the red dot laser module.

Here is the new diagram. What do you think?


That updated diagram looks good.

I don’t know what exact parts the pot and laser pointer are so:

  • I assume the laser dot takes 12V
  • I assume the pot is correctly wired. I know the pot type pictured in the diagram has a wiper in an unusual place but it is usually marked on its side.

After the DC supply is wired in I recommend testing all the outputs before you hook anything to it.
Then hook up each load in turn (least critical items first) and test them, with the last being the controller.

After everything is wired and the voltage for each termination is measured fill out the table and we will verify that everything looks normal.

Note: for the “IN” measurement put the pot approximately in the middle of its travel.

To Fill in the table:
If you highlight the table in this post
Then click “quote”
A post will open with the tables formatting in place
Just change the values of the “x’s” to your measured values

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I note that in the diagram above it is connected to 5V and 5V is at least a common voltage for the red dot lasers, which also often run off two or three button cells. So it’s at least reasonable for it to be 5V.

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Your right (and well said btw). I was thinking that mine is 12V and wondered if that one was also.

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I ordered one yesterday, thanks!

I tried switching the wires from the POT, but its not reading right.

This is the POT I’m using.

Having the POT wired this way I start at 0 volts and by turning the knob clockwise i can go all the way to 5 volts.

Why did you change the pot wiring?
I was just warning you that I remembered the wiring to be strange…

As long as the IN pin reads 0-5V when the pot it turned clockwise you are good.

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Ok, I’m gonna leave it like it was.
I found a PSU from an old PC, I’m gonna try to pull 5 and 12 volts to power the Nano and some accessories and do the testings while the new PSU arrives.

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I don’t know if you know this and I am not sure I remember it right but:
You have to have a min load on these PC power supplies for them to regulate correctly.
I had a gaggle of problems using these PC supplies until I found this out.

This may not be an issue since you are running the Nano using the 5V rail but thought I would mention it in case it acted weird :slight_smile:


Note: A 9 Watt load resistor is included but not soldered to the board. In our experience most modern ATX supplies don’t require a significant load on the 5 volt rail to start. An artificial load just wastes electricity and creates unnecessary heat. Please let us know your experience.

I have one of these attached to a Thermaltake ATX PSU, and I didn’t solder in the load resistor. I didn’t see poor regulation on 5V. I now have two bench power supplies so I haven’t used the PSU breakout for a long time.

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Something to keep in mind. You may not see or recognize poor regulation unless you load the supply. How much load, I don’t know.

I used 5V with one 'scope channel on it several times, so not having noticed artifacts, my particular power supply was probably adequate without a dummy load.

Thank you both four your comments and links. I will keep that in mind!
I will be doing some test tonight. I’m keeping my fingers crossed.

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Hello Don, the K40 came back to life with the PC power supply (I’m still waiting on the one you recommended from amazon).
Having separate power supplies makes a big difference. It feels like it has more power.
You asked me to check the Gnd voltage on the Nano board, but I’m not sure how to do that.
My problem was the 20ma coming from the 5v (50 watts LPS) like you mentioned. I was not supposed to power anything else, just the POT. Can’t wait for the new dual PS to arrive!
I still need to send you all the voltages!

Hello Don!
These are the voltages using the temporary PC PS, missing the G and Gnd.