Re: microstepper overheating
Gently gently persuade the card out and replace the connector.
The fact it randomly went in wrong direction suggests those burnt pins are the Direction pins. This is common thing on drives when a wire comes loose.
You should be able to repair this easy enough for just a couple of quid.
The next question thou should be why did it happen.? Could just have been bad connection or trapped wire etc or the board it's self is on it's way out.
First I'd repair the old board and check all the wiring and see what happens. If still giving trouble you'll need to look deeper and maybe replace the card.