The datasheet for that motor at http://www.mitsumi.co.jp/latest/Catalog/pdf/motor_m49sp_2k_e.pdf says it is rated at 1A peak and has a resistance per winding of 4.6 ohms per phase. it therefore follows that if you use a non-chopping stepper driver such as the ancient L298N, the maximum voltage you can safely apply to the motor is 4.6V (and even that is the peak rating, it doesn't say whether that is a safe continuous current). The L298N has around 3V voltage drop at 1A, therefore the maximum you can safely use as the L298N motor input voltage is about 7.6V. So no wonder everything overheats at 12V.
I suggest you use a stepper motor driver based on the A4988 instead of the L298. The A4988 regulates the motor current, so if you set the current to 1A or less, you can power the A4988 board with up to 24V (the voltage rating of the motor). You can get A4988 boards from Pololu or eBay. Make sure that you get one that is set at 1A (or less) current - they are often shipped set to 1.5A.
Hello
thank you for your quick reply. That as hat I thinking but I eeeeeee2yhasanted confirmation.
Can you please tell me if this is hat you have sugested ?
Yes. That's basically the same thing as the Sparkfun board. It has a potentiometer on it. You set the pot to the lowest current that gives you acceptable motion. If the pot is set too high then the chip can get very, very hot (potentially over 100 C) and you may damage the motor. I expect with the current you need it should be barely warm to the touch.
