Wednesday, August 13, 2014

CNC Engraver Schematics (YOOCNC-NT65-3X)

If you have purchased one of the inexpensive (~$400-$500) CNC engravers / routers, you may experience the same frustration as me.  An almost complete lack of documentation!

It took a pair of calipers and some experimentation to determine that the particular machine I purchased was set up for 400 steps per millimeter of motion.  Determining this without measurement would involve knowing the steps/rev of the motor (typically 200), the pitch and number of starts of the lead screw, and the microstepping ratio of the stepper driver.  None of this information was in the poorly-written-and-loosely-translated document provided with the machine.

In the case of my machine, it turns out that the microstepping ratio was set for 8 microsteps / step (fixed by design), the stepper motor is 200 steps / revolution, the lead screw pitch is 2mm with two starts (4mm of motion per full revolution).

As documented by others, there are features (limit / homing switches, PWM speed control...) which can be relatively easily enabled, but are not standard features as shipped.  

All of this led me to strongly desire a definitive set of schematics for the controller box.  After considerable Google Engineering (searching), I found none.  So, a few hours spent with detailed photos I took of the circuit boards led to a (hopefully) complete set of schematics for the two boards.  I've double checked them, but can't vouch for their absolute accuracy, so use them at your own risk.

I've added reference designators to the parts lacking them, and added a few explanatory names / comments.  I'd appreciate any feedback on mistakes found, or clarifications needed.

Stepper Motor Control Board
Power Supply and Spindle Control Board


  1. Hi Steve, thanks for this, looks good.
    Just with your section in the J11 area, from using the Mach3 program it appears the pin numbers may actually be numbered vertically instead of horizontally. eg from the defaults in the program, the motor outputs are pins 2-9, and other output pins are 1, 14, 16 and 17 ( which would be the pins 1, 2, 6 and 8 in this diagram).
    I'm looking to somehow get the Mach3 software give an output signal to another microcontroller I'm using, to control a pneumatic cylinder.

  2. Jay, I think that Mach3 refers to the DB25 pin numbers (J10). The connector you are referring to, J11, is a dual-row header connector. Due to the different numbering conventions for DB25 vs DRH pinouts, the pin numbers do not match. I think that the J10 pin numbering does match Mach3.
    Thanks for your interest!

  3. I did a bit of work on cnczone a while back about one variant of these boards.
    Circuit here...



  4. Postby Cromaglious » 03 Feb 2015, 09:04

    I have looked at the nt65-3x and pings 22, 23, 24, 25 are all fed by one trace at each driver. So to adjust steps and decay a bit of wiring is required.

    Looking at look at C31, C32, C33. and you'll see the traces going to pin 22 and 24. The thru hole I believe feeds the bottom to pin 23 and 25. I'll have to pop the board out and flip it over and look under the heat sink to see what can be done. Cutting the trace between 22 and 24 and the heavier trace leave 22 going towards the cap and solder a jumper wire from the cap side of the trace to pin 24 would give 1/2 step.

    nt65-3x microstepping.
    I found the table for microstepping. It's pins 22 M2 and Pin 23 M1.

    1. Excitation Mode Settings
    The excitation mode can be selected from the following four modes using the M1 and M2 inputs. (The
    2-phase excitation mode is selected by default since both M1 and M2 have internal pull-down resistors.)
    M2 M1
    L L 2-phase 1 step 1290 steps per inch 0.0007874" step
    L H 1-2-phase 1/2 step 2540 steps per inch 0.0003937" step
    ------------------------ no 1/4 step --------------------
    H L 4W1-2-phase 1/16 step 20320 steps per inch 0.0000492" step
    H H 2W1-2-phase 1/8 step (default on nt65-3x) 10160 steps per inch 0.0000984" step

    M2 and M1 have internal pulldowns so if you cut trace going to pin 23 (2nd from the right on the bottom row) you'll switch the board to 1/2 step which is good for 0.00039" a step. or cut 22 and 23 (2nd from right on top and bottom) you'll set fullstep or 0.00079" a step. ... PA00PVSV3R

    has some good pictures for the chip and you can see M2 hooked up to S3.

    Current Decay is set at 100% on pins 24 and 25 which are pulled to Vdd

    Well tonight I lifted the pin 22's and it did switch to 16 micro step. Next time I'll lift all the pin 23s and then I'll get .00079 movement per step. I also added some wire to the probe connection and got my digitizer wizard working. Now to make a probe to handle updown probing as well as side probing. I'm not going to pay $89 for a probe! I also soldered in the headers for the 4 axis and limit switchs. The LPT port input pins, I've used 15 and 13 for estop and probe. Pins 10,11,12 will be used for X,Y,Z limit switch pairs.


  5. Hi Steve,

    Thanks again for doing this, it has been quite a help over the last year or so.
    I am trying to activate PWM on the Spindle (what I really want is to just be able to automatically turn the thing on and off in G Code), and it looks like theres wires connecting PWM from one pcb board to the other. I'm not sure if any other wires need to be added to get it to work? I've set the spindle up in Mach3 to be connected to pin 17, with active low disabled, with 'step and dir' port on pin 1 (I know there's no step and direction but that option is still there.) in the motor pins area. in the spindle tab I have activated 'PWM Enabled'. I'm unsure if 'Spindle relays' need to be enabled. Direction of the spin does not matter for me. Do you have any suggestions on how to get the spindle working?


  6. Just to add to my previous post, I got the Spindle working. There was a switch at the back of the control box which changed control from the dial on the front panel, to the mach3 program. Thanks.

    1. Hey Jay,
      How did you wire the spindle control between the PSU board and the Driver board? I cannot make out the designations on the driver board image..
      Alex B

  7. Hi Steve,

    thank you very much for that schematic. I drew a printed circuit board for power and spindle PWM control, and also have corrected the wiring diagram of the circuit. How can I send it to you?

    Tihomir Benko.

  8. And my e-mail is tihomir.benko (at) gmail (dot) com

  9. I have the same machine and I used it for a few years.
    Now resistor R5 on your schematics quickly burns every time I change it. Its value looks suspiciously low (1K is already enough to drive the optocoupler). Also the weirdly super large C11 capacitor (actually named C9 on the PCB) seems to be in reverse polarity. The whole STOP sub circuit just makes no sense to me.

    BUT, if I remove R5, the spindle will no more rotate anyway! I am really puzzled.

    For reference, I asked for help here btw

    1. Check the value of the two power resistors before replaceing R5 again,, I had the same problem and theese two suddenly was in the 7K range and will then put almost 50V over R5 and the optpcoupler ,, both fried. I just shorted the power resistors and removed R5.

  10. Hi Steve.
    Mainly thank you for the schematics it's been a long time from your post. I have a doubt about the steppes may be you could help me. What's the voltage consumption? I can't find any information about that.

    Could you help me?

    best regards