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Dead Surface Mount Allegro A4988.

Posted by Macflame 
Dead Surface Mount Allegro A4988.
August 20, 2019 12:52PM
I have a board which has a dead stepper driver chip. Underneath the driver is a set of pins marked 1. Dir 2. En(able) 3. STP and 4. GND. I just wondered if I could add an external stepper driver to run the x axis stepper motor? On the board manual it does show a 'Large Driver' going to the set of pins (there are four lots of matching pins.). Does anyone know if and how I could do this?
Re: Dead Surface Mount Allegro A4988.
August 20, 2019 07:49PM
Here is a good place to start

[reprap.org]


Electronics Technician / Computer Programmer
Re: Dead Surface Mount Allegro A4988.
August 20, 2019 10:00PM
Yes you can do this, but it presumes several things


1) its actually the A4988 that is dead and not the IO pins.
2) the A4988 isnt dead in such a way that it interferes with the IO lines
Re: Dead Surface Mount Allegro A4988.
August 21, 2019 11:33AM
Many thanks for the quick reply. I will have a look at that CNC board. I was hoping not to have to fiddle with the firmware as it is bespoke and uses a strange extension .cbd. I might just have to bite the bullet and use Marlin.
Re: Dead Surface Mount Allegro A4988.
August 26, 2019 02:11PM
In the end I used a HC3DPR0038 DRV4988 break out board wired as shown in the attached diagram. I used a 5v outlet on the control board, to power the driver and a LM2596 Power Supply Step Down from the PSU to get the additional 9v I needed for the stepper motor as per wiring instructions. The X motor moved! But unfortunately it noisily 'clunked' along rather than the smooth operation of the other axis. I checked the Vref and it was at 0.7v so I turned it down to 0.5v suspecting it was set too high. Still the same clunky movement. I shall check the model stepper motor to get a more accurate vref for it but is there anything else that could be amiss?
Attachments:
open | download - break out.png (10.9 KB)
Re: Dead Surface Mount Allegro A4988.
August 26, 2019 10:08PM
9v is probably not enough... check the voltage on capacitor under the stepper driver... if it says more than 12v use 12v.

make sure all microstepping switches are set to on
Re: Dead Surface Mount Allegro A4988.
August 27, 2019 06:53AM
Many thanks for the quick reply. I was wondering about using 12v that but concerned about exceeding the 9v input marked on the breakout board. I have also since worked out that the Vref should be 0.85v. The micro-stepping is 1/16th all switches on. I will try your suggestion and the new vref.

Edited 1 time(s). Last edit at 08/28/2019 11:16AM by Macflame.
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