I remember seeing something about current limiting, so it may protect itself, but it may not too (and burn out if it is taking too much current. You may want to (carefully because it may be hot enough to burn!) check the temperature of the A4988 when the motors are running. Output power is supplied to the pins labeled GND and VCC.

Ideal for CCTV UK mains plug Lead length: 3.6m 2.1mm DC output plug. All headers are 0.1" pitch for simple insertion into a breadboard.

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',' Input power can be supplied to either the DC barrel jack or the two pin header labeled + and.It features a UK mains plug and 2.1mm DC output plug with a 3.6m lead length. Please tell me why you connceted your Arduino to ground three times. Yes you can use common ground when using different supply voltages. You supply power to the Arduino only via the 12V line. So if there is no 12V it is no wonder that your Arduino does not work properly. A 12V, 2A switch mode power supply unit that is ideal for use with CCTV. The 5V line supplies power to your servo only.

The 3 ms pins set the microstepping mode you want, and again need to be either driven from the micro (if you want to change the microstep configuration from your program) or be tied high or low to set the microstep config you want. Tutorial: +5 volt power supply In this tutorial, we make 5 volts power for our logic circuit A LM7805 couples with two capacitors of 100uF and 10uF gets input voltage and produce a +5 volt output for us. 12V, 2A, In Line CCTV Power Supply, 2.1mm Plug. If you don’t connect them to a pin on the micro or a resistor or jumper to power or ground (which ever they need to work) the motor won’t run. I’d guess (without having looked at the driver schematic assuming it is available) that the pins don’t have internal pull up resistors or the pull ups are set to be disabled (reset and/or sleep asserted) if not connected. Why would this circuit need jumpers between ms1-ms2 ms2-ms3 on the drivers. It did not work initially until I added a jumper across reset and sleep pins on both the A4988 drivers.

Fritzing 12v power supply