If you are repeatedly burning the same chip, you may have some component drawing excess current from it. Measure the resistance from the pins to the positive of the power supply. See if there is a difference between that measured resistance and a similar pin on the other 5804 chip. Maybe your stepper is the problem, maybe the limiting resistor. All things considered you are cooking the chip because there is too much power drawn from it beyond what it can dissipate. Joe.
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