A4988 Stepper motor driver no determinable outputs

Hello,I am new to this forum and so I hope that I can explain what I am seeing (or not seeing to be accurate) properly. Also, my keyboard underwent cleaning by my Niece recently and has ceased to function properly, :wink: so expect spacing errors among others.

Pictures not available (no camera/webcam or cell 'phone WITH a camera).

I have recently purchased the above listed A4988 stepper motor driver and after spending several days wiring a test board and checking the wiring, I seated the board and proceeded to the calibration method listed in the PololuPres_V3.pdf.

The power supply is an ATX 300 watt supply using only the 5v output and ground (except for a temp connection to the 12vdc line for this test). This is/was powering two other circuits successfully.

The problem that I have encountered is that during the calibration process I can not measure any current on the Bipolar motor output pins as per the pdf. and there is no motor movement at all. The A4988 chip becomes slightly warm to the touch via the heatsink indicating that there is at least something going on. Here is a bit of a checklist…

Antistatic in place. Verified
Connected enable, ms1,ms2 and ms3 to gnd. Verified
Connected Sleep and reset together. Verified
Voltage measured at Sleep/Reset = 2.06 vdc. Verified
Connected Step and Direction to gnd. Verified
Connected 12vdc (ATX Power) to VMOT (as a temp hookup). Verified
Connected motor wires to terminal (1A 1B / 2A 2B) with multimeter (current mode) inline coil connections 2 A and 2B. Verified
Connected 5 vdc (ATX power) to VDD. Verified
Checked all gnd connection. Verified
Checked 12 vdc and 5 vdc on proper pins. Verified
Check for voltage short in circuit (prior to installing A4988 board) none located. Verified
Check header pins to solder points on A4988 circuit board. Verified
Connected 24 vdc supply to VMOT (required by motor) to see if low voltage was the problem, no go. Verified

The motor is a PM35S-048-HHC6 24 volt 600ma 5.5 ohm. Also tested with 4018x-07-04 5 v 1 amp bipolar motor.

I was also able to measure a small voltage on the via between the chip and the pot which ran from 1.3 to 0 depending on the pots position.

As stated, I get no current reading (0.0-0.1) at the output specified by the pdf, nor any of the other outputs. The motor does not twitch, vibrate, “sing”, moan groan or recite the Gettysburg Address (I could make a million with a motor like that!). I have also swapped motor leads (With the powers disconnected) as per instructions found on the web for identifying the proper motor connectors.

Respectfully request HELP! :slight_smile:


Hello, Eldraad.

Did you measure 2.06V on reset before connecting power to VDD? With power connected to VDD, you should see the VDD voltage on sleep and reset. I don’t see anything else particularly worrying about your description. A picture of your setup might really be helpful. Can you double-check your solder connections and make sure your heat sink is not shorting anything? Can you explain what you mean by “antistatic in place”?

- Ryan

Thank you for your quick reply!

The 2.06vdc is measured at the sleep/reset with the power applied. I just checked again after reading your message and still see the same.

The Antistatic in place just meant I was grounded during the procedure and there were no stray metal bits on the work surface.

As far as the heatsink is concerned, I elevated the board so the headers pins just clear the top surface of the board. This left plenty of room for the heatsink.

I also tested the individual pin (header) to board connection to see if there had been an area with no connection, everything checked fine, the solder appears to be good.

I probably shouldn’t add this part but until a few weeks ago it had been about 20 years since my last project :slight_smile: . I recently decided to try building a small hobby CNC machine and tried several circuits I had found. THEN I found your A4988 driver board…sigh…all of that time wasted building drivers and decided to use it for the Z axis. I rather like the small postage stamp size package!

As a final check, I have pulled the sleep and reset pins high with no change. At a loss so far.

My niece brought her cell phone to take pictures of the ckt. They are blurry and I have dropped the size and added sharpness.
The long blue wire to the right is connected to 12 vdc. The green jumper between the terminal blocks and the board was for ground (temp. for testing). The red and black wires leading off left were for future expansion, although a printed circuit is planned.

This image has the A4988 removed for viewing.

The final picture is the foil side of the board, hope you can make connections out.

At this point I have recreated the circuit on another spare proto board with just the basics connections, leaving out the ability to change step modes (they are all grounded at the pins instead of being selectable). The circuit does not seem to provide any “worthwhile” motor outputs (all seen as mv). I get a change at the via between IC and pot when the pot is rotated and some slight warmth on the IC. I have removed the heatsink as it did not appear needed at only 600ma (and the heat generated was minimal).

At this point I have no further ideas of my own other than connecting a clock to the step input and seeing if there is any change at the motor connections. I checked the surface components with a magnifying lens and see no damage. There was some “whitish” powder or such at the A4988 pins near the pot side of the IC but that may have been dust from the circuit board edge cut or something. I blew that out with air and rechecked on the off chance but still had the same lack of output.

2V on the sleep/reset net indicates some kind of problem. You should definitely be seeing the same voltage as VDD on this net. I do not see a ground connection from your 12V supply to the board. Can you reproduce the minimal wiring diagram on the product page? If not, can you draw a wiring schematic of your setup?

- Ryan

The ground for the 12 v is tied in at the terminal block at the upper right of picture (under the blue heatshrink tubing).

I had created a second protoboard without the step select variations. The difference there is that I pulled the reset and sleep pins high, which is what I did on the first board after you mentioned the problem with the 2.06. I even added a clock signal to the step input to see if I would get an output at the motor terminals but no go.

Unless I am missing something the board follows the minimum wiring on the product page with the following exceptions…
The selectable state of ms1-ms3 (verified at gnd) and the connection of the Vmot gnd to the circuit gnd. I had been reading the posts in the motor control forum during the weekend to find similar problems. I have seen few posts with the same conditions (no measurable output) but not the 2.06 v.

I do have a “ms paint” wiring of the way the first circuit was built which may help tracing the connections. As soon as I find it I will post it just for clarification.

Well, I do not have any more troubleshooting advice. It sounds like possibly your stepper motor driver was damaged.

If you contact us directly with your order information and mention this thread, we might be able to at least offer you a discount on a replacement.

- Ryan

Okay. I will contact and see what we will do. Thank you very much for your time and help. I WILL be ordering several more this week (if all goes well) as the product is too good to pass up.

Thanks again.

may i ask, Why do you have two caps in your circuit?

I know they recommend that you have one on the vmot and ground.
But whats the 2nd for?


The other cap is between VDD and GND, which should help stabilize the logic voltage.

- Ryan